Invasive Species Compendium

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Datasheet

Pomacea canaliculata
(golden apple snail)

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Datasheet

Pomacea canaliculata (golden apple snail)

Summary

  • Last modified
  • 15 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Host Animal
  • Preferred Scientific Name
  • Pomacea canaliculata
  • Preferred Common Name
  • golden apple snail
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Mollusca
  •       Class: Gastropoda
  •         Subclass: Caenogastropoda
  • Summary of Invasiveness
  • P. canaliculata is a freshwater snail native to parts of Argentina and Uruguay. The distribution of P.canaliculata has been steadily increasing since its introduction to Asia, primarily as a h...

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Pictures

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PictureTitleCaptionCopyright
Adult snails have a thick, light-brown shell, a horny operculum, a square-like body whorl, and a deeply channelled suture. The eggs are spherical and appear like clusters of grapes; they are bright strawberry pink.
TitleAdults and eggs
CaptionAdult snails have a thick, light-brown shell, a horny operculum, a square-like body whorl, and a deeply channelled suture. The eggs are spherical and appear like clusters of grapes; they are bright strawberry pink.
CopyrightIRRI
Adult snails have a thick, light-brown shell, a horny operculum, a square-like body whorl, and a deeply channelled suture. The eggs are spherical and appear like clusters of grapes; they are bright strawberry pink.
Adults and eggsAdult snails have a thick, light-brown shell, a horny operculum, a square-like body whorl, and a deeply channelled suture. The eggs are spherical and appear like clusters of grapes; they are bright strawberry pink.IRRI
Golden apple snail (Pomacea canaliculata) crawling under water in a taro field. Hawaii.
TitleHabit
CaptionGolden apple snail (Pomacea canaliculata) crawling under water in a taro field. Hawaii.
Copyright©Kenneth A. Hayes
Golden apple snail (Pomacea canaliculata) crawling under water in a taro field. Hawaii.
HabitGolden apple snail (Pomacea canaliculata) crawling under water in a taro field. Hawaii.©Kenneth A. Hayes
Close-up of adults (left) and eggs (right).
TitleAdult and eggs
CaptionClose-up of adults (left) and eggs (right).
CopyrightIRRI
Close-up of adults (left) and eggs (right).
Adult and eggsClose-up of adults (left) and eggs (right).IRRI
Shell morphology of Pomacea canaliculata; (a) neotype. (b) previously presumed holotype.
TitleShell morphology
CaptionShell morphology of Pomacea canaliculata; (a) neotype. (b) previously presumed holotype.
Copyright©Kenneth A. Hayes
Shell morphology of Pomacea canaliculata; (a) neotype. (b) previously presumed holotype.
Shell morphologyShell morphology of Pomacea canaliculata; (a) neotype. (b) previously presumed holotype.©Kenneth A. Hayes
The first indication of field damage is a reduced plant stand. The snails severe the plant stalks below the water level, the tillers are cut first and the leaves and stems consumed under water.
TitleField damage
CaptionThe first indication of field damage is a reduced plant stand. The snails severe the plant stalks below the water level, the tillers are cut first and the leaves and stems consumed under water.
CopyrightIRRI
The first indication of field damage is a reduced plant stand. The snails severe the plant stalks below the water level, the tillers are cut first and the leaves and stems consumed under water.
Field damageThe first indication of field damage is a reduced plant stand. The snails severe the plant stalks below the water level, the tillers are cut first and the leaves and stems consumed under water. IRRI
Shell morphology of Pomacea canaliculata; (c-e) Shells from an introduced population in Hawaii showing variation in shell morphology.
TitleShell morphology
CaptionShell morphology of Pomacea canaliculata; (c-e) Shells from an introduced population in Hawaii showing variation in shell morphology.
Copyright©Kenneth A. Hayes
Shell morphology of Pomacea canaliculata; (c-e) Shells from an introduced population in Hawaii showing variation in shell morphology.
Shell morphologyShell morphology of Pomacea canaliculata; (c-e) Shells from an introduced population in Hawaii showing variation in shell morphology. ©Kenneth A. Hayes
Close-up of damage caused by P. canaliculata on rice.
TitleDamage symptoms on rice
CaptionClose-up of damage caused by P. canaliculata on rice.
CopyrightIRRI
Close-up of damage caused by P. canaliculata on rice.
Damage symptoms on riceClose-up of damage caused by P. canaliculata on rice.IRRI
Pomacea canaliculata egg masses laid on stems of taro in Hawaii.
TitleEgg masses
CaptionPomacea canaliculata egg masses laid on stems of taro in Hawaii.
Copyright©Kenneth A. Hayes
Pomacea canaliculata egg masses laid on stems of taro in Hawaii.
Egg massesPomacea canaliculata egg masses laid on stems of taro in Hawaii.©Kenneth A. Hayes
Egg morphology of Pomacea maculata (a) & (b) and Pomacea canaliculata (c); note the differences in clutch size and individual egg size. Egg colour in both species varies from a deep pink to orange–pink. When eggs are about to hatch (d), the pink colour fades and the juveniles (arrowed) are visible beneath the calcareous shell. (Note varying scale bars, but all show 5mm) Reproduced from Hayes et al. (2012).
TitleEgg morphology
CaptionEgg morphology of Pomacea maculata (a) & (b) and Pomacea canaliculata (c); note the differences in clutch size and individual egg size. Egg colour in both species varies from a deep pink to orange–pink. When eggs are about to hatch (d), the pink colour fades and the juveniles (arrowed) are visible beneath the calcareous shell. (Note varying scale bars, but all show 5mm) Reproduced from Hayes et al. (2012).
Copyright©Kenneth A. Hayes
Egg morphology of Pomacea maculata (a) & (b) and Pomacea canaliculata (c); note the differences in clutch size and individual egg size. Egg colour in both species varies from a deep pink to orange–pink. When eggs are about to hatch (d), the pink colour fades and the juveniles (arrowed) are visible beneath the calcareous shell. (Note varying scale bars, but all show 5mm) Reproduced from Hayes et al. (2012).
Egg morphologyEgg morphology of Pomacea maculata (a) & (b) and Pomacea canaliculata (c); note the differences in clutch size and individual egg size. Egg colour in both species varies from a deep pink to orange–pink. When eggs are about to hatch (d), the pink colour fades and the juveniles (arrowed) are visible beneath the calcareous shell. (Note varying scale bars, but all show 5mm) Reproduced from Hayes et al. (2012).©Kenneth A. Hayes
Pomacea canaliculata critical point-dried penial sheath showing two glands on the dorsal surface and penis partially extended from penis pouch. Key = Green: apical sheath gland; yellow: medial penis sheath gland; pink: penis; blue: penis bulb and penis pouch; purple: prostate. Reproduced from Hayes et al. (2012).
TitlePenial sheath; Pomacea canaliculata
CaptionPomacea canaliculata critical point-dried penial sheath showing two glands on the dorsal surface and penis partially extended from penis pouch. Key = Green: apical sheath gland; yellow: medial penis sheath gland; pink: penis; blue: penis bulb and penis pouch; purple: prostate. Reproduced from Hayes et al. (2012).
Copyright©Kenneth A. Hayes
Pomacea canaliculata critical point-dried penial sheath showing two glands on the dorsal surface and penis partially extended from penis pouch. Key = Green: apical sheath gland; yellow: medial penis sheath gland; pink: penis; blue: penis bulb and penis pouch; purple: prostate. Reproduced from Hayes et al. (2012).
Penial sheath; Pomacea canaliculataPomacea canaliculata critical point-dried penial sheath showing two glands on the dorsal surface and penis partially extended from penis pouch. Key = Green: apical sheath gland; yellow: medial penis sheath gland; pink: penis; blue: penis bulb and penis pouch; purple: prostate. Reproduced from Hayes et al. (2012).©Kenneth A. Hayes
Radular morphology of Pomacea maculata (a & c) and Pomacea canaliculata (b & d). c & d are rachidian teeth.  All scale bars = 100 µm.
TitleRadular morphology of Pomacea maculata and Pomacea canaliculata
CaptionRadular morphology of Pomacea maculata (a & c) and Pomacea canaliculata (b & d). c & d are rachidian teeth. All scale bars = 100 µm.
Copyright©Kenneth A. Hayes
Radular morphology of Pomacea maculata (a & c) and Pomacea canaliculata (b & d). c & d are rachidian teeth.  All scale bars = 100 µm.
Radular morphology of Pomacea maculata and Pomacea canaliculata Radular morphology of Pomacea maculata (a & c) and Pomacea canaliculata (b & d). c & d are rachidian teeth. All scale bars = 100 µm.©Kenneth A. Hayes
Pomacea maculata critical point-dried penial sheath, showing two glands on the dorsal surface. Key = Green: apical sheath gland; Orange: basal penis sheath gland; Blue: penis bulb and penis pouch; Purple: prostate. Reproduced from Hayes et al. (2012).
TitlePenial sheath; Pomacea maculata
CaptionPomacea maculata critical point-dried penial sheath, showing two glands on the dorsal surface. Key = Green: apical sheath gland; Orange: basal penis sheath gland; Blue: penis bulb and penis pouch; Purple: prostate. Reproduced from Hayes et al. (2012).
Copyright©Kenneth A. Hayes
Pomacea maculata critical point-dried penial sheath, showing two glands on the dorsal surface. Key = Green: apical sheath gland; Orange: basal penis sheath gland; Blue: penis bulb and penis pouch; Purple: prostate. Reproduced from Hayes et al. (2012).
Penial sheath; Pomacea maculata Pomacea maculata critical point-dried penial sheath, showing two glands on the dorsal surface. Key = Green: apical sheath gland; Orange: basal penis sheath gland; Blue: penis bulb and penis pouch; Purple: prostate. Reproduced from Hayes et al. (2012).©Kenneth A. Hayes

Identity

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Preferred Scientific Name

  • Pomacea canaliculata

Preferred Common Name

  • golden apple snail

Other Scientific Names

  • Ampullaria australis d'Orbigny, 1835
  • Ampullaria canaliculata Lamarck
  • Ampullaria dorbignyana Philippi, 1852
  • Ampullaria gigas Spix, 1827
  • Ampullaria gualtieri d'Orbigny, 1835
  • Ampullaria insularum d'Orbigny, 1835
  • Ampullaria levior Sowerby, 1909
  • Ampullarium canaliculatus Lamarck, 1822
  • Ampullarium insularum d'Orbigny, 1835
  • Ampullarium sp.
  • Ampullarius canaliculata Lamarck, 1822
  • Ampullarius canaliculatus Lamarck, 1822
  • Ampullarius insularum Hamada & Matsumoto
  • Ampullarius insularus Chang
  • Pila canaliculata Lamarck, 1822
  • Pila canaliculata Lamarck, 1822
  • Pila sp.
  • Pomacea canaliculata chaquensis Hylton Scott, 1948
  • Pomacea canaliculate Lamarck
  • Pomacea cuprina Reeve, 1856
  • Pomacea gigas Spix, 1827
  • Pomacea insularis d'Orbigny, 1835
  • Pomacea insularum d'Orbigny, 1835
  • Pomacea insularus d'Orbigny, 1835
  • Pomacea lineata Spix, 1827

International Common Names

  • English: apple snail; Argentinian apple snail; channeled apple snail; channeled applesnail; golden miracle snail; golden mystery snail; golden snail; jumbo snail; South American applesnail

Local Common Names

  • Indonesia: keong mas; siput mirbai
  • Korea, Republic of: king snail
  • Philippines: bisocol; bisokol (Ilocano); bisukol (Ilocano); golden kuhol; kuhol
  • Spain: caracol manzana
  • Thailand: cherry snail
  • USA/Hawaii: bisocol

EPPO code

  • POMACA (Pomacea canaliculata)

Summary of Invasiveness

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P. canaliculata is a freshwater snail native to parts of Argentina and Uruguay. The distribution of P.canaliculata has been steadily increasing since its introduction to Asia, primarily as a human food resource but perhaps also by the aquarium trade, beginning around 1979 or 1980 (Mochida, 1991; Halwart, 1994a; Cowie, 2002; Joshi and Sebastian, 2006). Once introduced to an area, it spreads rapidly through bodies of water such as canals and rivers and during floods. It feeds on aquatic plants and can devastate rice (in South-east Asia), taro (in Hawaii) and other aquatic or semi-aquatic crops. It may out-compete native apple snails (Halwart, 1994a; Warren, 1997), prey on native fauna (Wood et al., 2005, 2006) and alter natural ecosystem function (Carlsson et al. 2004a). It is also an important vector of various parasites including the nematode Angiostrongyulus cantonensis, which causes human eosinophillic meningitis (Lv et al., 2011; Yang et al., 2013).

It is listed among ‘100 of the world's worst invasive species’ (Lowe et al., 2000). In the United States its transport between states is restricted (Gaston, 2006), as is its transport between islands in the Hawaiian archipelago (Tamaru et al., 2006). It is listed as a quarantine pest in Malaysia (Yahaya et al., 2006) and in Japan. Australia has strong quarantine restrictions and is particularly concerned about P. canaliculata (Cowie, 2005).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Mollusca
  •             Class: Gastropoda
  •                 Subclass: Caenogastropoda
  •                     Order: Architaenioglossa
  •                         Unknown: Ampullarioidea
  •                             Family: Ampullariidae
  •                                 Genus: Pomacea
  •                                     Species: Pomacea canaliculata

Notes on Taxonomy and Nomenclature

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The higher classification of the Gastropoda of Bouchet and Rocroi (2005) places Pomacea in the informal group Architaenioglossa of clade Caenogastropoda. 

Lamarck described the freshwater snail Ampullariacanaliculata in 1822 (Lamarck, 1822). The genus name Ampullaria is now considered a junior synonym of the genus name Pila (Cowie, 1997; ICZN, 1999), which is a genus of African and Asian Ampullariidae, and this species is placed in the genus Pomacea, a New World genus. Lamarck had previously described a different, fossil marine snail from France also as Ampullariacanaliculata (Lamarck, 1804). The resulting confusion over the name was resolved by ICZN (2002) following Cowie et al. (2001), and the name Pomaceacanaliculata for the South American ampullariid species is valid.

The original type locality of this species, as stated by Lamarck (1822), is ‘the rivers of Guadeloupe’. This Caribbean island type locality may have been in error (Hylton Scott, 1957; Thiengo et al., 1993) as the species is native to South America and does not occur naturally in Guadeloupe or elsewhere in the Caribbean. Hayes et al. (2012), in re-describing P. canaliculata, designated a neotype from Palermo, Buenos Aires, Argentina, which is now the correct type locality. Hayes et al. (2012) also clarified the distinction between P. canaliculata and P. maculata, the two main invasive species of Pomacea. The name Pomaceainsularum, formerly used as the valid name of P. maculata, is now a junior objective synonym of P. maculata, following the designation of a single specimen as both the neotype of P. maculata and lectotype of P. insularum; the same specimen was also designated as the neotype of P. gigas, thereby making this also a junior objective synonym of P. maculata (Hayes et al., 2012).

Various other scientific names have been used for P. canaliculata that place it in incorrect, invalid or mis-spelled genus names, that identify it as a different species, or mis-spell the species names.

In the past, the highly confused taxonomy of South American Ampullariidae led some authors to consider P.canaliculata to perhaps be extremely widely distributed naturally in South America (e.g. Cazzaniga, 2002; Cowie and Thiengo, 2003). However, the work of Hayes et al. (2008, 2009a, 2012), including both molecular and morphological analyses of variation among New World ampullariids, has shown that the range of P. canaliculata is restricted to the Lower Paraná, Uruguay and La Plata basins, although based on habitat similarity and watershed connections it is possible that it may also occur in the lower reaches of the Upper Paraná and parts of southern Brasil.

Prior to the work of Rawlings et al. (2007), Hayes et al. (2008, 2009a, 2012) and Tran et al. (2008), the difficulty of distinguishing P. canaliculata from P. maculata meant that not only were their true ranges in South America not understood but also that the correct identities of ampullariids in Asia and other locations to which they have been introduced were not known. Thus, much of the literature published prior to these clarifications, especially in Asia, either confounded data from these two species (e.g. Cowie 2002) or may have presented data from one species that in fact were derived from the other.

This confusion has meant that the common name most widely used in Asia, ‘golden apple snail’, or GAS (Joshi and Sebastian, 2006) — ‘golden’ either because of the colour of their shells, which is sometimes a bright orange-yellow, or because they were seen as an opportunity for major financial success when they were first introduced — in fact refers to two species, P.canaliculata and P. maculata. The name golden apple snail has also been used for an entirely different species, P. dolioides (incorrectly identified as P. lineata), in Suriname (Wiryareja and Tjoe-Awie, 2006). Similarly, the name ‘channeled apple snail’ (or ‘applesnail’), an anglicization of the specific epithet ‘canaliculata’, was originally applied to populations in the United States that were thought to be P. canaliculata, but turned out in fact to be P. maculata (Howells et al., 2006; Rawlings et al., 2007). Additional confusion has also arisen because some of these names have been used for more than one species of ampullariid; for instance, ‘golden snail’ and ‘mystery snail’ have been used primarily for orange/yellow varieties of both P. canaliculata and P. diffusa (the latter often misidentified as P. bridgesii), notably in the aquarium trade, in some cases without realizing that they are different species, or without being able to distinguish them, or simply misidentifying them (see Cowie et al., 2006).

Description

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The most thorough description available is by Hayes et al. (2012), in which P. canaliculata and P. maculata are compared. The following brief description is modified from that publication. 

Adults

The adult shell is thin, smooth and ~35-60 mm in height. It coils dextrally – that is, when viewed with the apex uppermost the aperture is on the right side of the shell. Fully grown females are larger than males. The colour is yellow-brown to greenish-brown or dark chestnut, sometimes with dark brown spiral bands of variable number and thickness. The whorls are rounded and the suture between the whorls is deeply channelled. The shell spire is generally low. The aperture is generally ovoid to kidney-shaped, and the inside lip of the shell is unpigmented.

The operculum (the trap-door like structure attached to the upper part of the animal’s foot and used to close the shell aperture when the animal withdraws into the shell) is also brown; it is horny (corneous) in texture and flexible, and is uniformly concave in females, but concave at the centre and becoming convex toward the margins in males.

The foot is oval with a squarish anterior edge. The tentacles are long and tapering, highly extensible and with large but short eye stalks at their outer bases. The snout is short, squarish and with lateral, anterior tips elaborated into long tapering labial palps. The neck is modified on the left into a long, extensible siphon. The mantle cavity is deep and broad, occupying a third to half of the body whorl. In males the penis sheath is visible just behind the mantle edge above the right tentacle. The lung occupies most of the left side of the mantle and the gill is situated in the mantle roof, anterior to the lung and just posterior to the base of the siphon.

Eggs and Hatchlings

The eggs are spherical, calcareous, deep pink-red to lighter orange-pink, becoming paler as the calcium hardens, and eventually whitish pink just before hatching. They are laid above water on emergent vegetation and other firm substrates (e.g. bridge pilings, rocks). The height of deposition above water varies from a few centimetres to ~2 metres. The number of eggs per clutch averages ~260, ranging from as few as 12 to as many as ~1000 (Tamburi and Martín, 2011). Individual egg diameter is ~3.00 mm. One-day-old hatchlings are ~2.6 mm wide and 2.8 mm in height. When they hatch, they drop from where the eggs were laid into the water below.
 

Distribution

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Native Distribution

The taxonomic confusion surrounding P.canaliculata has meant that its true natural range has not been clear. Many species that molecular studies have shown to be distinct (Hayes et al., 2008, 2009b), had in the past been confused with P. canaliculata, to the extent that some authors suggested that many of these nominal species might well be synonyms of P. canaliculata and therefore that its range extended throughout much of South America (see Hylton Scott, 1957; Cazzaniga, 2002, 2006; Cowie, 2002). The natural range of P. canaliculata is now known to be much more restricted, consisting of the Lower Paraná, Uruguay and La Plata basins, although based on habitat similarity and watershed connections it is possible that it may also occur in the lower reaches of the Upper Paraná and parts of southern Brazil. It is not present in the Amazon basin.

Its southern limit in Argentina seems to be limited by temperature (Seuffert and Martín, 2009) and this may limit is spread to higher latitudes in its invaded range (Seuffert et al., 2010, 2012).

Non-Native Distribution

P.canaliculata was introduced to Taiwan from Argentina in 1979-1981 but has now spread to most countries of Southeast and East Asia, with much of the rice-growing areas Taiwan, Japan and the Philippines especially infested (Mochida, 1991; Naylor, 1996; Joshi and Sebastian, 2006). In the Pacific, P. canaliculata was introduced to Hawaii by 1989, although there are unverified anecdotal accounts that it was present by 1983 or 1984 (Cowie, 1995b; Levin et al., 2006; Cowie et al., 2007). It was also recorded in Guam in 1989 (Smith, 1992). In North America P.canaliculata is now present in California, Arizona and Florida (Rawlings et al., 2007; K.A. Hayes, unpublished). The first and so far only record in Europe is from the Ebro Delta in Spain. This record (López et al., 2010) is of P.maculata, but subsequent data suggest that both P. maculata and P. canaliculata may be present.

Winter temperatures may limit the northern spread of P. canaliculata in Japan (Ito, 2002), although it can alter its behaviour and acclimate to these cooler temperatures to some degree, permitting over-wintering further north than would otherwise be possible (Wada and Matsukura 2007, Matsukura et al., 2009).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

BangladeshAbsent, unreliable recordIntroducedRanamukhaarachchi and Wickramasinghe, 2006; Wu and Xie, 2006Records contain no details or citation
CambodiaAbsent, unreliable recordIntroduced1985 Invasive Cowie, 1995a; Cowie, 2002; Pol, 2002; Halwart and Bartley, 2006; Lv et al., 2011; EPPO, 2014Reports probably refers to Pomacea maculata
ChinaWidespreadIntroduced1981-1985 Invasive Cowie et al., 2002; Halwart, 1994a; Halwart and Bartley, 2006; Wu and Xie, 2006; Yin et al., 2006; EPPO, 2014
-ChongqingLocalisedIntroducedLv et al., 2011
-FujianWidespreadIntroduced1985Halwart, 1994a; Mochida, 1991; Yin et al., 2006; Lv et al., 2011; EPPO, 2014
-GuangdongWidespreadIntroduced1988Halwart, 1994a; Mochida, 1991; Wu and Xie, 2006; Yin et al., 2006; Lv et al., 2011; EPPO, 2014
-GuangxiWidespreadIntroducedHalwart, 1994a; Lv et al., 2011; EPPO, 2014
-GuizhouWidespreadIntroducedLv et al., 2011
-HainanWidespreadIntroducedLv et al., 2011; EPPO, 2014
-Hong KongWidespreadIntroduced1980-1987Cowie, 2002; Kwong et al., 2008New Territories and Tsing Yi island only
-HubeiLocalisedIntroducedLv et al., 2011
-HunanWidespreadIntroducedLv et al., 2011
-JiangxiWidespreadIntroducedLv et al., 2011
-ShanghaiLocalisedIntroducedLv et al., 2011
-SichuanLocalisedIntroducedLv et al., 2011; EPPO, 2014
-YunnanWidespreadIntroducedLv et al., 2011; EPPO, 2014
-ZhejiangPresentIntroduced1985Halwart, 1994a; Mochida, 1991; Yin et al., 2006; Lv et al., 2011; EPPO, 2014
IndiaAbsent, unreliable recordIntroducedRanamukhaarachchi and Wickramasinghe, 2006; Wu and Xie, 2006No details or citation
IndonesiaPresent, few occurrencesIntroduced1981-1984 Invasive Halwart, 1994a; Mochida, 1991; Halwart and Bartley, 2006; Hendarsih-Suharto, et al., 2006; EPPO, 2014Bali, Nusa Tengarra, Lombok
-Irian JayaPresent, few occurrencesIntroducedHendarsih-Suharto, et al., 2006; EPPO, 2014
-JavaPresentIntroduced1989Mochida, 1991; Naylor, 1996; Hendarsih-Suharto, et al., 2006; Hayes et al., 2008; EPPO, 2014
-KalimantanPresent, few occurrencesIntroduced Invasive Hendarsih-Suharto, et al., 2006
-Nusa TenggaraPresent, few occurrencesIntroduced Invasive Hendarsih-Suharto, et al., 2006West Timor, Madura, Lesser Sunda Islands
-SulawesiWidespreadIntroduced Invasive Hendarsih-Suharto, et al., 2006; EPPO, 2014Including the island of Buton
-SumatraPresentIntroduced1989Naylor, 1996; Cowie, 2002; Hendarsih-Suharto, et al., 2006; EPPO, 2014
IraqPresentAl-Jassany and Al-Hassnawi, 2017
IsraelPresentEPPO, 2014
JapanWidespreadIntroduced1981 Invasive Mochida, 1991; Halwart and Bartley, 2006; Wada, 2006; EPPO, 2014
-HonshuPresentIntroduced Invasive Halwart, 1994a; Wada, 2006; Hayes et al., 2008; EPPO, 2014
-KyushuPresentIntroduced1981 Invasive Wada, 2006; Hayes et al., 2008; EPPO, 2014
-Ryukyu ArchipelagoPresentIntroducedbefore 1984Cowie, 2002; Wada, 2006; EPPO, 2014
-ShikokuPresentIntroducedHalwart, 1994a; Wada, 2006
Korea, Republic ofPresentIntroduced1981-1986 Invasive Mochida, 1991; Halwart and Bartley, 2006; Lee and Oh, 2006; Hayes et al., 2008; EPPO, 2014In aquaculture in Suwon
LaosPresentIntroduced1991-1994Douangboupha and Khamphoukeo, 2006; Halwart and Bartley, 2006; Hayes et al., 2008; EPPO, 2014
MalaysiaPresentIntroduced1987 Invasive Halwart and Bartley, 2006; Yahaya et al., 2006; EPPO, 2014
-Peninsular MalaysiaPresentIntroduced1987-1991Naylor, 1996; Cowie, 2002; Yahaya et al., 2006
-SabahPresent, few occurrencesIntroduced1992 Invasive Teo SuSin, 2004; Yahaya et al., 2006; Hayes et al., 2008; EPPO, 2014
-SarawakRestricted distributionIntroduced1987Mochida, 1991; Naylor, 1996; Yahaya et al., 2006
MyanmarPresent, few occurrencesIntroduced Invasive Hayes et al., 2008
PhilippinesWidespreadIntroduced1980-1982 Invasive Mochida, 1991; Naylor, 1996; Adalla and Magsino, 2006; Halwart and Bartley, 2006; EPPO, 2014
SingaporePresentIntroduced1993Cowie, 2002; Halwart and Bartley, 2006
Sri LankaAbsent, invalid recordEpa, 2006Only Pomacea diffusa is currenlty known from Sri Lanka
TaiwanWidespreadIntroduced1979-1981 Invasive Mochida, 1991; Cheng and Kao, 2006; Halwart and Bartley, 2006; Yang et al., 2006; EPPO, 2014; EPPO, 2014
ThailandPresentIntroduced1982-1990Mochida, 1991; Halwart and Bartley, 2006; Hayes et al., 2008; EPPO, 2014
VietnamWidespreadIntroducedaround 1988 Invasive Cuong, 2006; Halwart and Bartley, 2006; Huynh, 2006; Hayes et al., 2008; EPPO, 2014

Africa

EgyptAbsent, unreliable recordIntroducedWu and Xie, 2006
South AfricaAbsent, unreliable recordIntroducedBerthold, 1991Identified as Pomacea lineata but probably P. canaliculata

North America

CanadaAbsent, formerly presentIntroduced Not invasive Howells et al., 2006Identification uncertain. Did not survive over winter.
MexicoPresentIntroduced2013Campos et al., 2013
USARestricted distributionIntroducedHowells et al., 2006; Rawlings et al., 2007; EPPO, 2014
-AlabamaPresentEPPO, 2014
-ArizonaPresent, few occurrencesIntroduced2005Howells et al., 2006; Rawlings et al., 2007; EPPO, 2014Colorado River at Yuma
-CaliforniaPresentCerutti, 1998; Howells et al., 2006; Rawlings et al., 2007; EPPO, 2014
-FloridaAbsent, invalid recordRawlings et al., 2007; EPPO, 2014
-GeorgiaRestricted distributionEPPO, 2014
-HawaiiWidespreadIntroduced1989 Invasive Cowie et al., 2007; Tran et al., 2008; EPPO, 2014Anecdotal reports of its presence in 1983 or 1984
-LouisianaPresentEPPO, 2014
-South CarolinaPresent, few occurrencesEPPO, 2014
-TexasAbsent, invalid recordIntroduced2000Neck, 1986; Neck and Schultz, 1992; EPPO, 2014

Central America and Caribbean

Dominican RepublicPresentIntroduced1990/1991 Invasive Rosario and Moquete, 2006; Hayes et al., 2012; EPPO, 2014

South America

ArgentinaWidespreadNative Not invasive Hayes et al., 2008; Hayes et al., 2012; EPPO, 2014
BoliviaAbsent, invalid recordCowie and Thiengo, 2003; EPPO, 2014In light of taxonomic revision (Hayes et al., 2012), Pomacea canaliculata does not occur in Bolivia
BrazilAbsent, invalid recordCowie and Thiengo, 2003; EPPO, 2014In light of taxonomic revision (Hayes et al., 2012), Pomacea canaliculata is not known from Brazil, although it may be present in southern Brazil
-Mato GrossoAbsent, invalid recordNative Not invasive
-Rio Grande do SulAbsent, invalid recordNative Not invasive
-Sao PauloAbsent, invalid recordNative
ChilePresent, few occurrencesIntroducedbefore 2008Letelier and Soto-Acuna, 2008Laguna Conchali, Los Vilos
ColombiaPresent, few occurrencesIntroducedHayes et al., 2012
ParaguayAbsent, invalid recordCowie and Thiengo, 2003; EPPO, 2014In light of taxonomic revision (Hayes et al., 2012), Pomacea canaliculata does not occur in Paraguay
SurinameWidespread
UruguayPresent, few occurrencesNative Not invasive Hayes et al., 2008; Hayes et al., 2012; EPPO, 2014Maldonado, Montevideo

Europe

SpainPresent, few occurrencesIntroduced2009 Invasive Baker, 1998; Lopez et al., 2010; Anonymous, 2011; EPPO, 2014Possible confusion with Pomacea lineata

Oceania

AustraliaAbsent, intercepted onlyPlant Health Australia, 2009
GuamPresentIntroduced1989-1992Smith, 1992; Cowie, 2002; Halwart and Bartley, 2006; Hayes et al., 2008
Papua New GuineaPresentIntroduced1990-1993Laup, 1991; Halwart and Bartley, 2006; Orapa, 2006; EPPO, 2014Port Moresby, Lae, Waghi Valley.

History of Introduction and Spread

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P. canaliculata was introduced to Taiwan from Argentina in 1979-1981 (Mochida, 1991; Naylor, 1996; Cheng and Kao, 2006). In the course of the 1980s and early 1990s it spread to most countries of southeast and eastern Asia (Mochida, 1991; Naylor, 1996). Molecular analysis confirmed Argentina, and specifically Buenos Aires province, as the source of the species and suggested multiple independent introductions (Hayes et al., 2008). It had become well established and a major rice pest within a very few years; for instance, large areas in Taiwan, Japan and the Philippines were infested by 1986 (Mochida, 1991; Naylor, 1996). The specific dates of introduction to the various countries given by authors differ in some cases, though not dramatically; this is probably because they are based on anecdotal or hearsay information, sometimes years old, rather than on formal or official records.

In the Pacific, P. canaliculata was introduced to Hawaii by 1989, although there are unverified anecdotal accounts that it was present by 1983 or 1984 (Cowie, 1995b; Levin et al., 2006; Cowie et al., 2007). It was deliberately introduced as a food resource, almost certainly from the Philippines (Tran et al., 2008). It has also been seen in the domestic aquarium trade in Hawaii. It was also recorded in Guam in 1989 (Smith, 1992), purportedly accidentally introduced, but whether it is established there is not known.

P. canaliculata has also been introduced to North America. It was first recorded in California in 1997, possibly associated with the pet trade (Cerutti, 1998), but it may also have been introduced for human consumption, possibly from Hawaii or the Philippines, as Californian populations share the single haplotype found in Hawaii, which is also the most common haplotype in the Philippines (Rawlings et al., 2007; Tran et al., 2008). P.canaliculata has also been verified in Arizona (Rawlings et al., 2007), first reported from there in 2005 (Howells et al., 2006). It is also in Florida (Rawlings et al., 2007; K.A. Hayes, unpublished).

The first and so far only record in Europe is from the Ebro Delta in Spain, where it was first recorded in 2009. This record (López et al., 2010) is of P. maculata, but subsequent data suggest that both P. maculata and P. canaliculata may be present.

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Arizona by 2005 No No Howells et al. (2006)
California Philippines by 1997 Aquaculture (pathway cause) No No Rawlings et al. (2007) Deliberate introduction
California by 1997 Pet trade (pathway cause) No No Cerutti (1998) Possible aquarium release
Cambodia early 1990s Aquaculture (pathway cause) Yes No Preap et al. (2006) Deliberate introduction, possibly from Thailand
Canada 2002 Pet trade (pathway cause) No No Howells et al. (2006) Aquarium release
Chile before 2008 No No Letelier and Soto-Acuna (2008)
China Asia 1981 Aquaculture (pathway cause) Yes No Mochida (1991); Wu and Xie (2006) Deliberate introduction, possibly from Taiwan
Dominican Republic 1991 No No Rosario and Moquete (2006) Possibly deliberate introduction (to clean fish production ponds); maybe from Taiwan.
Egypt   No No Wu and Xie (2006)
Florida by 2007 No No Rawlings et al. (2007)
Guam Taiwan 1989 Hitchhiker (pathway cause) No No Smith (1992) Accidentally imported in a shipment of fish fry
Indonesia 1986 Pet trade (pathway cause) Yes No Hendarsih-Suharto, et al. (2006) Deliberate introduction
Japan Taiwan 1981 Aquaculture (pathway cause) Yes No Wada (2006) Deliberate introduction
Korea, Republic of Japan 1981-1983 Aquaculture (pathway cause) Yes No Lee and Oh (2006) Deliberate introduction
Laos Thailand 1991 Yes No Douangboupha and Khamphoukeo (2006)
Laos Vietnam 1994 Aquaculture (pathway cause) Yes No Douangboupha and Khamphoukeo (2006) Deliberate introduction
Malaysia 1991 Aquaculture (pathway cause) ,
Pet trade (pathway cause)
Yes No Yahaya et al. (2006) Deliberate introduction
Myanmar China early 1990s Aquaculture (pathway cause) Yes No Deliberate introduction
Papua New Guinea Philippines 1990 Aquaculture (pathway cause) Yes No Laup (1991); Orapa (2006) Deliberate introduction
Philippines Taiwan 1982 Aquaculture (pathway cause) Yes No Adalla and Magsino (2006); Mochida (1991) Deliberate introduction
Philippines Argentina 1984 Aquaculture (pathway cause) Yes No Adalla and Magsino (2006); Mochida (1991) Deliberate introduction
South Africa South America 1988 Pet trade (pathway cause) No No Berthold (1991) Deliberate introduction
Spain 2009 Yes No Lopez et al. (2010) Possibly associated with fish farms. Possible confusion with P. maculata
Taiwan Argentina 1979-1981 Aquaculture (pathway cause) Yes No Cheng and Kao (2006) Deliberate introduction
Thailand Yes No
Vietnam Philippines around 1990 Aquaculture (pathway cause) Yes No Cuong (2006) Deliberate introduction
Vietnam Taiwan early 1990 Aquaculture (pathway cause) Yes No Cuong (2006) Deliberate introduction

Risk of Introduction

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The primary mode of spread of P. canaliculata has been deliberate introduction to new areas by people who see it as a potential source of food. Although usually confined initially to aquaculture facilities, the snails either escape or are deliberately released into agricultural or natural wetlands. This has happened despite knowledge of its serious pest status in areas already invaded. It has also been reported as having been introduced by the pet trade, although the main ampullariid in the pet trade is P. diffusa rather than P. canaliculata. Nonetheless it is known in the pet trade, and this has been thought of as the pathway of its introduction to Spain (Anonymous, 2011). Once introduced, it is further possible that it spreads naturally by floating downstream, to a limited extent by crawling upstream, during flooding, and even attached to birds (Levin et al., 2006). People also move it around accidentally; for instance, in Hawaii small juveniles have been inadvertently transported on taro parts used for propagation (Levin et al., 2006), and eggs can be transported on boats (Baker et al., 2012).

P.canaliculata spread rapidly through much of Southeast Asia following its initial introduction to Taiwan. It has now probably reached most areas in which it would be able to live within the region. However, modelling its distribution in China under global warming scenarios indicates that it could spread north into areas that it has not yet invaded (Lv et al., 2011). Similar range expansions related to climate change could also occur elsewhere, for instance in Korea and Japan. It has not yet been reliably reported from India or Bangladesh, but based on climate matching these countries are susceptible, as are parts of Australia (Baker, 1998). Similarly, climate matching combined with two global warming scenarios identified areas in Europe that may be susceptible (Baker et al., 2012).

In general, P. canaliculata was not well liked as a food in Asia and markets did not develop (e.g. Wada, 1997; Cheng and Kao, 2006; Preap, 2006; Wada, 2006; Yang et al., 2006; Yin et al., 2006), although in parts of southern China it became a popular delicacy, eaten raw (Cowie, 2013; Yang et al., 2013). Deliberate introduction for food may therefore now be rare. Introduction by the aquarium trade (and via disposal of the contents of domestic aquaria) may also be rare, as P. canaliculata is not the most common ampullariid in the trade (but see Baker et al., 2012). Nonetheless, major new invasions may arise from the introduction of small propagules. Natural expansion of already introduced populations is probably important, and accidental introduction by people remains possible. Great caution is recommended when considering P. canaliculata as a biological control agent for aquatic weeds (Cazzaniga and Estebenet, 1985) and it is only appropriate in areas in which P. canaliculata is already established (Wada, 1997; Cazzaniga, 2006). Internet or mail order trade of ampullariids occurs, but the relative contribution to this trade of P. canaliculata specifically has not been assessed. 

P. canaliculata is legally considered as a quarantine pest, or a potential pest should it be introduced, in a number of countries, such as Australia (Plant Health Australia, 2009), China (Yang et al., 2013), Malaysia (Yahaya et al., 2006), Spain (Baker et al., 2012), USA (Gaston, 2006) and Vietnam (Cuong, 2006; Huynh, 2006). Other countries may also consider it a quarantine pest.

Habitat

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P. canaliculata is a freshwater snail restricted to wetland areas that are flooded for at least part of the year. It generally occurs in relatively still water in marshes, swamps, ditches, irrigation canals, ponds and lakes lined with vegetation and generally with muddy bottoms. It is thus well suited for living in rice paddies, taro patches and similar artificial habitats. It can survive harsh environmental conditions caused by pollutants in the water (e.g. Lach and Cowie, 1999), and because it can breathe air it can live in waters with low dissolved oxygen levels. In Hong Kong, Kwong et al. (2008) were able to predict the distribution of P. canaliculata with some accuracy, but the water chemistry differed considerably from that in its native range (Martín et al., 2001).

Habitat List

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CategoryHabitatPresenceStatus
Freshwater
Irrigation channels Principal habitat Harmful (pest or invasive)
Irrigation channels Principal habitat Natural
Lakes Secondary/tolerated habitat Harmful (pest or invasive)
Lakes Secondary/tolerated habitat Natural
Ponds Principal habitat Harmful (pest or invasive)
Ponds Principal habitat Natural
Reservoirs Secondary/tolerated habitat Harmful (pest or invasive)
Reservoirs Secondary/tolerated habitat Natural
Rivers / streams Secondary/tolerated habitat Harmful (pest or invasive)
Rivers / streams Secondary/tolerated habitat Natural
Terrestrial-managed
Cultivated / agricultural land Secondary/tolerated habitat Harmful (pest or invasive)
Ricefields Principal habitat Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Wetlands Principal habitat Harmful (pest or invasive)
Wetlands Principal habitat Natural

Hosts/Species Affected

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The list of crops and other plants affected is not an exclusive list of all wild plant species potentially affected. P. canaliculata is primarily a generalist macrophyte herbivore and determining what plants it does not eat may be more important than generating a long list of plants it will eat (Cowie, 2002).

Regarding the most important crop affected, rice, it is the young seedling stage that is most vulnerable (Halwart, 1994a; Okuma et al., 1994b; Schnorbach, 1995; Naylor, 1996; Cowie, 2002; Wada, 2004). All parts of wetland taro plants are eaten because the snails can access the leaves when they droop down to the water surface.

Because of its generalist feeding habits, P. canaliculata has been suggested as a biological control agent for aquatic and wetland weeds in rivers (Cazzaniga and Estebenet, 1985; Fernández et al., 1987) and rice fields (Okuma et al., 1994b; Wada, 1997; Joshi et al., 2006). It can be used to control weeds without eating the rice plants only if rice seedlings are transplanted and at the 3-leaf stage (21 days), so that they are too tough for the snails to eat, and the ground is allowed to dry until water is introduced to a 2 cm depth after 6-8 days after transplanting (Joshi et al., 2006).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Ageratum conyzoides (billy goat weed)AsteraceaeOther
Alternanthera philoxeroides (alligator weed)AmaranthaceaeOther
Amaranthus tricolorAmaranthaceaeOther
Apium graveolens var. dulce (celery)ApiaceaeOther
Astragalus sinicus (chinese clover)FabaceaeOther
Azolla (waterfern)AzollaceaeMain
Azolla pinnata (mosquito fern)AzollaceaeWild host
BacopaScrophulariaceaeWild host
CitrusRutaceaeOther
Colocasia esculenta (taro)AraceaeMain
Commelina diffusa (spreading dayflower)CommelinaceaeOther
Cyperus (flatsedge)CyperaceaeWild host
Cyperus difformis (small-flowered nutsedge)CyperaceaeWild host
Echinochloa (barnyardgrass)PoaceaeWild host
Echinochloa glabrescensPoaceaeWild host
Egeria densa (leafy elodea)HydrocharitaceaeMain
Eichhornia crassipes (water hyacinth)PontederiaceaeWild host
Eleocharis dulcis (Chinese water chestnut)CyperaceaeOther
Fimbristylis littoralis (lesser fimbristylis)CyperaceaeWild host
Hibiscus manihot (Hibiscus root)MalvaceaeOther
Hydrocotyle sibthorpioidesApiaceaeOther
Ipomoea aquatica (swamp morning-glory)ConvolvulaceaeWild host
Juncus (rushes)JuncaceaeWild host
Lactuca sativa (lettuce)AsteraceaeOther
Lemna (duckweed)LemnaceaeWild host
Ludwigia adscendens (water primrose)OnagraceaeOther
Monochoria vaginalis (pickerel weed)PontederiaceaeWild host
Murdannia nudiflora (doveweed)CommelinaceaeOther
Myriophyllum (watermilfoil)HaloragidaceaeWild host
Nelumbo nucifera (sacred lotus)NelumbonaceaeWild host
Neptunia oleraceaFabaceaeOther
Nymphaea (waterlily)NymphaeaceaeOther
Oenanthe [plant: genus]ApiaceaeOther
Oryza sativa (rice)PoaceaeMain
Paspalum distichum (knotgrass)PoaceaeWild host
Phragmites australis (common reed)PoaceaeOther
Pistia stratiotes (water lettuce)AraceaeWild host
Polygonum barbatum (knot grass)PolygonaceaeOther
Ranunculus sceleratusRanunculaceaeOther
Rorippa (yellowcress)BrassicaceaeOther
Sagittaria (arrowhead)AlismataceaeOther
Salvinia molesta (Kariba weed)SalviniaceaeWild host
Sphenoclea zeylanica (wedgewort)SphenocleaceaeWild host
TrapaTrapaceaeWild host
Trapa natans (waterchestnut)TrapaceaeOther
Typha latifolia (broadleaf cattail)TyphaceaeOther
Utricularia (bladderwort)LentibulariaceaeOther
VallisneriaHydrocharitaceaeOther
Vigna (cowpea)FabaceaeWild host
Zannichellia palustrisZannichelliaceaeWild host
Zea mays (maize)PoaceaeOther
Zizania (wild-rice)PoaceaeWild host
Zizania latifolia (manchurian wildrice)PoaceaeWild host

Growth Stages

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Symptoms

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In wetland rice the first symptom of damage by P. canaliculata is a reduced plant stand where the snails have severed the plant stalks below the water level. The tillers are cut first and then the leaves and stems are consumed under water. The crop is highly vulnerable at the early seedling stage. In taro, damage to the corms is readily visible, and active snails are easily seen feeding on both corms and leaves that have drooped so that their tips break the water surface.

List of Symptoms/Signs

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SignLife StagesType
Leaves / external feeding
Stems / external feeding
Vegetative organs / external feeding

Biology and Ecology

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The biology of ampullariids has been reviewed by Cowie (2002) and Cowie and Hayes (2012), among others, with much of the information in these review articles derived from P. canaliculata. However, given the taxonomic confusion, in particular between the invasive species P. canaliculata and P. maculata, some of the studies reviewed by Cowie (2002) may have confused these and perhaps other ampullariid species. For instance, we now know that fig. 1 of Cowie (2002) in fact illustrates P. maculata and not P. canaliculata, although the legend identifies the snails as P. canaliculata. Some more recent studies may also have confounded these species, as they were not rigorously distinguished and identified until the studies of Rawlings et al. (2007) and Hayes et al. (2008, 2009a, 2012). Unless otherwise indicated, much of the information in this section on biology and ecology is from Cowie (2002) and Cowie and Hayes (2012).

Genetics

The chromosome number of P. canaliculata is n = 14 (Mercado-Laczkó and Lopretto, 1998; Diupotex-Chong et al., 2004). Variation in DNA sequences has been reported by Rawlings et al. (2007) and Hayes et al. (2008, 2009a, 2012). Matsukura et al. (2008) reported a genetic approach to distinguish P. canaliculata and P. maculata. Matsukura et al. (2013) reported genetic exchange and possible hybridization between P. canaliculata and P. maculata.

Reproductive Biology

P. canaliculata is dioecious (has separate sexes), internally fertilizing and oviparous. Females tend to be larger than males. Eggs are laid in clutches above water on the exposed parts of vegetation, rocks, etc., perhaps to avoid aquatic predators or in response to low oxygen tension in their often near-stagnant aquatic habitats. The eggs are enclosed in a calcium carbonate shell, which may or may not be used as a source of calcium for the developing embryo. Their bright pink colour serves as a warning to predators and the eggs as a result have very few predators (see also Dreon et al., 2010). These bright pink eggs are often the first visible signs of an infestation. Clutch size is very variable but averages about 260 eggs. Oviposition takes place predominantly at night, or in the early morning or evening, about a day after copulation. On each occasion a single clutch is laid. Copulation takes place about three times per week and occurs at any time of day or night, although there may be some diurnal rhythm, and it takes 10-18 hours. The interval between successive ovipositions has been reported to be from 5 to 14 days. Hatching generally takes place about 2 weeks after oviposition, but this period varies greatly and development is highly dependent on temperature (Koch et al., 2009). Newly hatched snails immediately fall or crawl into the water. The estimated average annual output of P. canaliculata is about 4400 eggs (Barnes et al., 2008)

All aspects of the life history are influenced by temperature (Sueffert et al., 2010, 2012). A laboratory study of P. canaliculata in its native Argentina (Estebenet and Cazzaniga, 1992) demonstrated the crucial role of temperature in growth and reproduction. At a constant 25°C, snails matured in 7 months and then bred continuously for a single ‘season’ of about 4 months, then died. In contrast, under seasonally fluctuating temperatures (7-28°C), the snails took 2 years to reach maturity; they then bred for two distinct annual breeding seasons, for a life-span of about 4 years. In the wild in Argentina, P. canaliculata breeds only during the summer (Hylton Scott, 1957), and the life-cycle under the fluctuating laboratory temperature regime may indeed reflect the life-cycle in the wild. Under semi-artificial conditions in Japan (an outdoor pond but with food provided), P. canaliculata grew to maturity in less than two months (Chang, 1985). In tropical regions of South-east Asia, release from the seasonality of its natural range may be at least one reason why P. canaliculata is so prolific; rapid growth and breeding, and hence rapid succession of generations, are permitted year round (Naylor, 1996), leading to rapid population expansion and high population densities.

Males must attain a minimum age, regardless of size, for the onset of reproductive maturity, whereas females must reach a minimum size regardless of age (Estoy et al., 2002; Tamburi and Martín, 2009).

Physiology and Phenology

Mortality of P. canaliculata is high at water temperatures above 32–35°C, although in one study little reduction in activity levels occurred over five days at 35°C (Seuffert et al., 2010). It can survive 5–20 days at 0°C, two days at -3°C and six hours at -6°C (Mochida, 1991; Wada and Matsukura, 2007; Matsukura et al., 2009), although activity almost stops below 10 °C (Seuffert et al., 2010). However, Wu and Xie (2006) suggested that the snails introduced to China are less tolerant of cold temperatures.

Longevity

Cowie (2002), citing various sources, reported longevity of P. canaliculata ranging from 119 days to 5 years, based on data from Argentina, the Philippines, Japan, Hawaii and Taiwan (these reports probably do refer to P. canaliculata and not P. maculata), with higher temperatures leading to shorter longevity.

Activity Patterns

In the temperate regions where P. canaliculata is native, it only breeds during summer. Locally, variation in reproductive regime may be related to local climatic variation, especially availability of water. In their introduced humid tropical Southeast Asian range and the controlled environment of a rice paddy, P. canaliculata can grow and breed year round as long as sufficient water is present. In Hong Kong, it reaches full size in four to six months and reproduction occurs almost year round, although with some variation in snail biomass and density related to water temperature (Kwong et al., 2010). Under artificial conditions P. canaliculata can grow even faster. In cooler regions such as Japan, as paddies dry out and temperatures drop during winter, the snails bury into the mud and become dormant, awaiting warmer temperatures and reflooding of the paddies in spring. P. canaliculata is only reported to survive buried for up to three months (Schnorbach, 1995). Winter temperatures may limit the northern spread of P. canaliculata in Japan (Ito, 2002), although it can alter its behaviour and acclimate to these cooler temperatures to some degree, permitting over-wintering further north than would otherwise be possible (Wada and Matsukura 2007, Matsukura et al., 2009). Its southern limit in Argentina seems to be limited by temperature (Seuffert and Martín, 2009) and this may limit is spread to higher latitudes in its invaded range (Seuffert et al., 2010, 2012).

Population Size and Density

Densities of P. canaliculata in rice paddies in the Philippines generally are 1-5 m-2 but densities up to 150 m-2 have been reported (Halwart, 1994a; Schnorbach, 1995). Anderson (1993), perhaps mistakenly, reported ‘1,000 mature snails per square metre’ in the Philippines. In rice in Japan, studies have reported 3-7 m-2 (Okuma et al., 1994b) and 12-19 m-2 (Litsinger and Estano, 1993). In Hawaii, densities of P. canaliculata in taro patches have been recorded at over 130 m-2 (Cowie 2002). Following hatching, densities in the immediate vicinity of the clutch will be high. However, few reports are sufficiently detailed to assess the impact of survivorship on density, although P. canaliculata is clearly able to achieve remarkably high adult population densities.

Nutrition

Most ampullariids, including P. canaliculata, are generalist herbivores. P.canaliculata grows rapidly when fed on numerous plant species (e.g. Lach et al., 2000; Qiu and Kwong, 2009; Wong et al., 2010). Growth rate generally correlates with feeding on the preferred plant(s). Some species will feed on other animals, including frogs, bryozoans and other smaller snails and their eggs, mostly but not always as carrion (e.g. Wood et al., 2005, 2006; Kwong et al., 2009; Wong et al., 2009; R.H. Cowie, personal observations). In Hong Kong, detritus was found more frequently than macrophytes in the stomachs of P. canaliculata; the snails also ate cyanobacteria, green algae and diatoms (Kwong et al., 2010). The predominant habit, however, is macrophytophagous, which from a pest standpoint is also the most significant. P. canaliculata (and P. maculata) seem particularly voracious and generalist compared to other Pomacea species (Morrison and Hay, 2011).

Environmental Requirements

P. canaliculata reaches its southernmost limit in the Southern Pampas of Argentina, part of its natural South American range, at 37 °S (Seuffert et al., 2010). Its northern limit, in its non-native range, is 36 °N, in Japan (Ito, 2002), around 31 °N in China (Lv et al., 2011) and between 40 and 41 °N in Spain (Anonymous, 2011), assuming both P. canaliculata and P. maculata not just the latter are present in the Ebro Delta, Spain.

Climate

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ClimateStatusDescriptionRemark
Af - Tropical rainforest climate Preferred > 60mm precipitation per month
Am - Tropical monsoon climate Preferred Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
Aw - Tropical wet and dry savanna climate Preferred < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
36 37

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Anabas testudineus Predator Juveniles not specific
Anas platyrhynchos Predator Adult not specific China, Malaysia, Philippines, Taiwan, USA, Vietnam Rice, taro
Anastomus oscitans Predator Adults not specific
Anax parthenope Predator Juveniles not specific
Carassius gibelio Predator Juveniles not specific
Centropus sinensis Predator Adults not specific
Chinemys reevesii Predator Adults not specific
Clarias batrachus Predator Juveniles not specific
Clarias gariepinus Predator Juveniles not specific
Conocephalus maculatus Predator Eggs not specific
Corvus macrorhynchos Predator Adult not specific
Cybister japonicus Predator Juveniles not specific
Cyprinus carpio Predator Adult not specific Japan, Vietnam Rice
Eleotris oxycephala Predator Juveniles not specific
Eretes sticticus Predator Juveniles not specific
Eriocheir japonicus Predator Adults not specific
Geothelphusa dehaani Predator Adults not specific
Homocoryphus longipennis Predator Eggs not specific
Leptobarbus hoevenii Predator Juveniles not specific
Luciola lateralis Predator Adults/Juveniles not specific
Macrobrachium formosense Predator Juveniles not specific
Macromia amphigena Predator Juveniles not specific
Malayemys subtrijuga Predator Juveniles not specific
Marisa cornuarietis Predator
Mauremys japonica Predator Adults not specific
Mylopharyngodon piceus Predator Juveniles not specific China, Japan, Taiwan, Vietnam Rice
Ompok bimaculatus Predator Juveniles not specific
Oreochromis niloticus Predator Juveniles not specific
Osphronemus exodon Predator Juveniles not specific
Pantala flavescens Predator Juveniles not specific
Pomacea canaliculata Predator Juveniles not specific
Pristolepis fasciata Predator Juveniles not specific
Procambarus clarkii Predator Juveniles not specific
Pseudogobio esocinus Predator Juveniles not specific
Rattus Predator
Rattus norvegicus Predator Adult not specific
Rattus tanezumi Predator Adults not specific
Solenopsis geminata Predator Eggs/Juveniles not specific
Trachemys scripta Predator Adults not specific
Tribolodon hakonensis Predator Juveniles not specific
Trionyx sinensis Predator Adults not specific
Zacco platypus Predator Juveniles not specific

Notes on Natural Enemies

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The best known natural enemies of apple snails in general are vertebrates. Throughout much of their natural range in South America, snail kites (Rhostramus sociabilis) and limpkins (Aramus guarauna) are major predators of various apple snail species, which are their almost exclusive food (Peterson, 1980; Perera and Walls, 1996). The ranges of both these species overlap with that of P. canaliculata and they are probably significant predators. In parts of South America, large piles of apple snail shells can accumulate under the favorite perches of snail kites (R.H. Cowie, personal observations).

Apple snails, perhaps including P. canaliculata, are a major component of the diet of caiman lizards (Dracaena spp.) in South America (Perera and Walls, 1996).

In its non-native range, P. canaliculata is eaten by a large number of predators. A non-exhaustive list was provided by Yusa (2006) and included 46 species in 16 orders, including insects (Hemiptera, Orthoptera, Hymenoptera, Odonata, Coleoptera), crustaceans (Decapoda), fish (Cypriniformes, Perciformes), reptiles (Testudines), leeches (Arhynchobdellae), birds (Anseriformes, Passeriformes, Ciconiiformes, Cuculiformes) and mammals (Rodentia). Some key references mention particular predators: perch (Anabas testudineus) and freshwater crabs (Esanthelphusa nimoafi) (Carlsson et al., 2004b), dragonfly (Pantala flavescens) larvae (Ichinose et al., 2002), common carp (Cyprinus carpio) (Yusa et al., 2001; Ichinose et al., 2002), Asian openbill (Anastomus oscitans) (Sawangproh and Poonswad, 2010) and rats (Rattus norvegicus) (Yusa et al., 2000). P. canaliculata adults themselves will prey on juveniles (Yusa et al., 2006).

The bright pink eggs of P. canaliculata are generally thought of as being unpalatable to predators. However, eggs and small juveniles are eaten by fire ants, Solenopsis geminata, in Asia, and these have been suggested as possible biocontrol agents (Way et al., 1998; Yusa, 2001), though introduction of such a major invasive pest would probably be inappropriate. A hemipteran and two orthopterans also eat the eggs of P. canaliculata (Yusa, 2006).

A wide range of species of animals, including leeches, crustaceans, insects, fish, amphibians and turtles, as well as mallards (Anas platyrhybchos) and rats (Rattus norvegicus) have been tested experimentally in the laboratory to determine their effectiveness as predators of P. canaliculata (Yusa et al., 2006).

All the information on natural enemies of P. canaliculata in its non-native range in the Natural Enemies table is from Yusa (2006). Species that prey on adults no doubt also prey on juveniles.

Means of Movement and Dispersal

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Short term dispersal activity does not necessarily translate into long term, long distance dispersal. P. canaliculata may spread naturally predominantly by floating downstream, although crawling upstream is also possible, unless the flow rate is too great (Ranamukhaarachchi and Wikramasinghe, 2006). However, the rapid spread of P. canaliculata within Asia and Hawaii following introduction has been predominantly human mediated.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
AquacultureIntroduced as human food. Most impotant long distance pathway Yes Yes
Biological controlP. canaliculata has been suggested as a weed control agent in rice paddies Yes Yes
Flooding and other natural disastersPerhaps important in Asia where large areas are flooded during the wet season Yes
Hitchhiker Yes Yes
Intentional releaseReleased into rice paddies and taro fields to provide human food Yes
Interconnected waterwaysCan be transported passively downstream and can crawl upstream to a limited extent Yes
Pet tradeSome instance reported but not major pathway globally. Probably release by aquarium owners Yes Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Aircraft Yes
Aquaculture stock Yes Yes
Clothing, footwear and possessions Yes
Host and vector organismsCarried by birds Yes
Land vehiclesCargo ships/boats Yes
Mail Yes
Plants or parts of plants Yes
Ship hull fouling Yes Yes
Soil, sand and gravel Yes
Water Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark eggs; juveniles Yes Pest or symptoms usually visible to the naked eye
Leaves eggs; juveniles Yes Pest or symptoms usually visible to the naked eye
Roots adults Yes Pest or symptoms usually visible to the naked eye
Seedlings/Micropropagated plants eggs; juveniles Yes Pest or symptoms usually visible to the naked eye
Stems (above ground)/Shoots/Trunks/Branches Yes Pest or symptoms usually visible to the naked eye
Wood eggs; juveniles Yes Pest or symptoms usually visible to the naked eye

Impact Summary

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CategoryImpact
Animal/plant collections Negative
Animal/plant products Negative
Biodiversity (generally) Negative
Crop production Negative
Economic/livelihood Positive and negative
Environment (generally) Negative
Fisheries / aquaculture Negative
Forestry production None
Human health Negative
Native fauna Negative
Native flora Negative
Rare/protected species Negative
Tourism Negative
Trade/international relations Negative
Transport/travel Negative

Impact

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In its natural range, P. canaliculata has been considered ‘harmless and useless’, as it is neither an important crop pest nor human health hazard and it is not used as a human food or for any other purpose (Cazzaniga, 2006). However, where it has been introduced, it has caused serious economic harm, has become a human health problem in some regions, and has the potential to have serious environmental and biodiversity impacts.

Economic Impact

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P. canaliculata can infest paddy crops including rice (Oryza sativa), lotus (Nelumbo nucifera), taro (Colocasia esculenta), swamp cabbage (Ipomoea aquatica), mat rush (Juncus decipiens), watercress (Rorippa spp.), Japanese parsley (Oenanthe stolonifera), water chestnuts (Trapa bicornis), wild rice (Zizania latifolia), azolla (Azolla spp.), and water lilies (Nymphaea spp.) (Mochida, 1991; Chompoonut, 1998), as well as, no doubt, other less important crops. In particular, snail damage to rice is a major problem in South-east and East Asian countries. Dryland crops such as maize, citrus and ramie (Boehmeria nivea) have been reported to be attacked (Adalla and Morallo-Rejesus, 1989), but this seems unlikely to happen under normal field conditions as P. canaliculata does not habitually disperse or move long distances over land and does not feed out of water.

Asia

In the Philippines, farmers have considered P. canaliculata to be the most serious pest of rice (Halwart, 1994a). The infested area expanded rapidly from 300 ha in 1986 to 426,000 ha in 1988 and had reached more than 800,000 ha by 1995 (Cagauan et al., 1998; Cagauan and Joshi, 2003). In 1990, all 13 regions of the Philippines had infestations (Rice IPM Network, 1991). A 1999 survey by the Department of Agriculture-Philippine Rice Research Institute indicated that 35% of 71 provinces in various regions of the Philippines identified P. canaliculata as a pest in rice farms (Adalla and Magsino, 2006). Yield loss also increased from ca 2500 t in 1985 to 25,000 t in 1991 (Rice IPM Network, 1991). Pesticide expenditure for 1988 was estimated to be US$2.4 million (Halwart, 1994a). Yield loss of rice due to P. canaliculata in 1990 was estimated at 70,000 to 100,000 t, valued at US$12.5-17.8 million, with the total cost including yield loss, replanting cost and the cost of control (molluscicides and hand picking), estimated at US$28-45 million (Naylor, 1996). The cumulative costs after P. canaliculata invasion up to 1990 were estimated as between US$425-1,200 million (Naylor, 1996). Since then, there have been claims that P. canaliculata infestation has decreased due to the spread of integrated management approaches (Cagauan and Joshi, 2003). However, in 2003, of about 3 million ha of rice fields in the Philippines about 1.4 million ha were infested (Adalla and Magsino, 2006).

In Thailand, P. canaliculata (possibly confounded with P. maculata) became a major rice pest in the early 1990s. Paddy fields infested by the snails increased from 3822 ha in 8 provinces in 1990 to 64,623 ha in 43 provinces in 1996 (Aroonpol, 1997). The extent of damage in 42 provinces in 2001 was 141,257 ha (Sinives, 2002). Plant losses in Chiang Mai and Lamphun Provinces in 1994-1996 were 8.8 and 27.3%, respectively (Chompoonut, 1997). The Thai Government spent US$880-38,000 every year in the mid-1990s for a snail control campaign that encouraged farmers to collect snails and egg masses (Chompoonut, 1997, 1998) and in the decade of the 2000s they spent approximately US$1 million per year to control Pomacea (perhaps including both P. canaliculata and P. maculata) (Sawangproh and Poonswad, 2010).

In Malaysia, P. canaliculata (possibly confounded with P. maculata) was introduced many times during the 1990s. Various efforts were made to destroy the populations and eradication was successful in some areas. For example, 10 ha of infested paddy fields in Kuala Semeling, Kedah, were successfully cleared by the introduction of seawater in 1991. However, infested paddy areas expanded gradually, and about 1000 and 5000 ha were affected in Peninsular Malaysia and Sabah, respectively, in 1998. The total cost of the operation up to 1998 was estimated at about US$590,000 (Jambari et al., 1998). By 2002, about 17,400 ha were infested and the snails were present in all states except Terengganu (Yahaya et al., 2006).

In Vietnam, P. canaliculata (possibly confounded with P. maculata) has caused serious damage to rice and swamp cabbage (Ipomoea aquatica), in particular in the Cuu Long Delta, where farmers practice direct seeding of rice. By 1994, rice fields in 32 of 50 provinces were infested and by 1997 rice fields in 57 of 61 provinces (some provinces were split), with infested areas increasing from 1,678 ha to 109,715 ha (Cuong, 2006). Infested areas of swamp cabbage reached 3479 ha in 1997 (Cuong, 2006). Total funds for control of apple snails were 2079 million VND (ca US$100,000).

In Laos, P. canaliculata, first reported in 1991 and the first damage to rice reported in 1992, is now present in all provinces (Douangboupha and Khamphoukeo, 2006). Economic costs are not readily available.

In Cambodia, it is not clear whether P. canaliculata has been definitively recorded  or has been confused with P. maculata (Hayes et al., 2008). Apple snails were discovered in 1995 and had spread to at least nine provinces by 1998 (Cowie, 1995a; Chim, 1998; Preap et al., 2006). With the exception of one small area, they do not appear to be causing serious damage to crops in Cambodia (the reason for this is not known) and no economic costs are available (Preap et al., 2006).

In Indonesia, only P. canaliculata has been definitively reported, albeit only from a single location (Hayes et al., 2008), whereas apple snails are widely distributed in the country and P. maculata may also be present (Hendarsih-Suharto et al., 2006). Apple snail damage in rice fields was reported in 1995 from only 12 districts in West Java, but by 1999 it had extended to 16 districts, and within 3 years the damage had multiplied by 5-170 times (Hendarsih-Suharto, 2002). No economic costs are readily available.

In Taiwan, 13,000 ha of rice fields were infested by P. canaliculata in 1983, increasing to 151,444 ha by 1986, and the area treated with molluscicides and the estimated loss in paddy fields increased from 46,000 ha and US$8.3 million to 90,000 ha and US$30.9 million (Mochida, 1991). Annual expenditure on molluscicides was US$1 million in 1982-1990 but in 2002-2003 had been reduced (for budgetary reasons and not because of the lack of need for control) to US$170,000-300,000 (Cheng and Kao, 2006). Annual figures of US$200 million and US$175.6 million have been given for costs of damage in the ‘agricultural and ecological environment’, by Cheng and Kao (2006) and Yang et al. (2006), respectively.

In mainland China, P. canaliculata was first recorded in Guangdong province in 1981 and by 1988 the damaged area had grown to 130,000 ha in 37 counties in the province (Wu and Xie, 2006). It is now much more widespread in China (Lv et al., 2011). Damage to rice has gradually increased relative to the increasing levels of direct-seeded rice in South China. No economic costs are readily available.

In Japan, the first record of rice damage caused by P. canaliculata was reported in 1984 (Yusa and Wada, 2002) and in the same year P. canaliculata was designated as a quarantine pest by the Japanese Government. Since then its distribution gradually expanded until by 1998 it occurred in 28 prefectures throughout south and central Japan (Wada, 2006). By 2004, it had infested 770,000 ha of rice fields, about 60% of this area being in Kyushu (Wada, 2006). The level of damage may have stopped increasing during the 1990s because of the application of various control methods. However, P. canaliculata is still a serious pest in areas of Kyushu where very young seedlings are transplanted and where it rains heavily during the transplanting season. In addition, the presence of the snail is a constraint in promoting direct seeding in Kyushu (Wada, 1997, 2006; Yusa and Wada, 1999). No economic costs are readily available.

Hawaii

In Hawaii, following its introduction in 1989 or earlier, P. canaliculata spread widely during the 1990s (Lach and Cowie, 1999) and continued to spread subsequently (Cowie et al., 2007). In 2004, the farm value of taro was reported as US$2.7 million, but with 18-25% lost as a result of damage by P. canaliculata (Levin et al., 2006). It had dropped in 2005 to $2.2 million (Levin, 2006). Between 1989 and 2005, official agency (as opposed to individual farmer) costs of control projects in Hawaii were almost $400,000 (Levin, 2006).

North America

Any reports concerning apple snails in Texas (USA) refer to P. maculata (Rawlings et al., 2007), and so far this species does not seem to have become a major problem in rice fields. P. canaliculata is only present in Arizona, California and Florida (Rawlings et al., 2007) and there are no records of it causing economic damage. Nonetheless, Pomacea species in general are ranked extremely high on a list of gastropod pests of quarantine significance in the USA (Cowie et al., 2009).

South America

In Suriname, another species of Pomacea, P. dolioides (incorrectly identified by some authors as P. lineata), is a rice pest that appears to have become a pest following the change from transplanted to direct seeded rice in the 1950s (van Dinther, 1956; Litsinger and Estaño, 1993; Wiryareja and Tjoe-Awie, 2006). Otherwise, there had been no reports of apple snails as pests until 1993, when several hectares of young rice in southern Brazil were seriously infested and 30% of seedlings disappeared; thereafter, rice damage was sporadically observed every year and was subsequently found in all regions of the state by 1997 (Petrini et al., 1998). However, this report may not refer to P. canaliculata, which has not been confirmed as present in southern Brasil, based on modern molecular techniques, although it may be there (Hayes et al., 2012). In Argentina, P. canaliculata is not generally considered a pest, although, since the second half of the 1990s, a few farmers have experienced heavy damage to dry-seeded rice following heavy rain (Wada, 1999).

Factors Affecting Losses

The status of P. canaliculata as a rice pest differs among countries and regions. Because germinating seeds are much more susceptible to the snail than transplanted seedlings (Wada et al., 1999), P. canaliculata is a more important rice pest in countries where direct seeding is widely practised, such as in the Philippines, Thailand and Vietnam. It is well controlled after transplanting by keeping paddy water shallow if the fields are well levelled (Wada, 1997). Therefore, the infrastructure of fields and irrigation schemes influence the pest's status. Climate is also important. For example, 90% of the total area damaged by P. canaliculata in Japan has always been in Kyushu, where it rains heavily in the transplanting season, thus flooding the fields. During the seeding season, no or only very few snails were found in most paddy fields in Brazil (though they may not be P. canaliculata; Hayes et al., 2012), even though the snails were distributed in waterways; natural enemies such as birds and fish may result in the low snail density in South America (Wada, 1999).

Loss of rice seedlings due to P. canaliculata is influenced by the size and density of the snail and by plant age. Snails larger than 16 mm cause damage to transplanted seedlings. Snails with a shell height of 29, 39, 48 and 57 mm consumed 4.5, 6.3, 12.6 and 23.5 seedlings (2.5-leaf stage) per day, respectively. The amount of consumption has been shown to be proportional to the cube of shell height, according to the relationship Y=0.12Xn+0.26, where Y = daily number of missing seedlings, X = shell height in cm (Oya et al., 1986). Another relationship, Y=0.85Xn+5.77, was obtained for 20-day-old plants by Ozawa and Makino (1997), who also estimated the relationship Y=100(1- exp(-0.12Z)) between daily number of missing seedlings (Y) and the snail density /m² (Z). They estimated that 2, 4 and 8 snails (25 mm shell height)/m² causes 5, 27 and 72% missing rice hills. Yamanaka et al. (1988) reported that snails with shell heights of 21, 31, 40 and 51 mm consumed 1.7, 3.7, 6.6 and 7.0 seedlings (3.1 leaf stage), resulting in 0.06, 0.5, 1.0 and 1.1 missing hills per day, respectively. A threshold for initiating control in transplanted paddies was proposed as 2.0 snails/m² (Ozawa and Makino, 1997). In the Philippines, Basilio (1991) reported that 0.5, 1 and 8 snails (20-30 mm shell height)/m² caused 6.5, 19 and 93% missing rice hills.

In wet direct seeding, P. canaliculata is a more harmful rice pest. A single snail (24 mm shell height) can prevent the establishment of more than 400 germinating seeds (Wada et al., 1999). Thus, a lower control threshold in direct seeding of 0.5 snails/m² has been proposed in Japan (Kiyota and Sogawa, 1996).

Environmental Impact

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Impact on Habitats

In Thailand, Carlsson et al. (2004a) showed that P. canaliculata had a serious impact on aquatic vegetation, with high densities causing almost complete loss of plants as well as resulting in high nutrient concentrations and high phytoplankton biomass (caused by increased phosphorus levels in the water as a result of snail grazing on aquatic plants), and hence turbid water. In this way the snails caused a major change in ecosystem state and function. In other studies, in Laos, Carlsson and Lacoursière (2005) and Carlsson and Brönmark (2006) also showed that P. canaliculata at natural densities caused major loss of plant biomass, of both macrophytes and periphyton. And in experiments in a pond in Hong Kong, similar result were found, although phosphorus content of the water was not heightened in the treatments with P. canaliculata (Fang et al., 2010).

Impact on Biodiversity

P. canaliculata has been suggested as the cause of the decline of native Asian species of freshwater snails, including native apple snails in the genus Pila, perhaps via competition (Halwart, 1994a). In the Phililppines, native Pila spp. are reported to have declined as a result of pesticide applications to control P. canaliculata (Anderson, 1993).

P. canaliculata will also prey on other species of aquatic snails (Cazzaniga, 1990; Kwong et al., 2009), although its potential population level impact is not known. However, other ampullariid species have been introduced to various localities in attempts to control the snail vectors of schistosomes, and have had major impacts on those snail populations. Thus, in Guadeloupe, introduced P. glauca and Marisacornuarietis caused the decline of Biomphalaria glabrata through competition (Pointier et al., 1988, 1991). In Puerto Rico, M. cornuarietis caused a decline in B. glabrata and Lymnaea columella through predation (Robins, 1971; Peebles et al., 1972). M. cornuarietis is said to have had a similar effect in the Dominican Republic (Perera and Walls, 1996) and in Egypt (Demian and Kamel, cited by Cedeño-León and Thomas, 1983; Berthold, 1991). Native snail species may well, therefore, be threatened by the introduction of P. canaliculata.

In addition, P. canaliculata will prey on other organisms. For example, P. canaliculata feeds on bryozoans and was thought to be a significant factor in the absence of bryozoans from locations in which they would be expected to occur (Wood et al., 2005, 2006). Other ampullariids are reported to prey on other animals (Cowie, 2002), not only as carrion but also as live animals, e.g. fish (McLane, 1939).

Social Impact

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The economic impacts of P. canaliculata have major impacts on the livelihoods of the individual farmers affected. P. canaliculata also has other important direct impacts on human wellbeing, notably its impact on human health.

P. canaliculata is of serious human health concern in a number of regions as it acts as a vector for a number of parasites that cause human diseases, including schistosomes that cause dermatitis and a fluke that causes intestinal problems (Hollingsworth and Cowie, 2006). Most notably, however, it can act as a host of Angiostrongylus cantonensis, the rat lungworm, which can infect humans if ingested and cause potentially fatal eosinophilic meningitis. This disease, which can also be caused by other things, is known as angiostrongyliasis or rat lungworm disease. Although many species of gastropods can act as hosts of A. cantonensis (Wallace and Rosen, 1969; Kim et al., 2013; Thiengo et al., 2013), P. canaliculata is of particular significance in southern China, where it has become a delicacy when eaten raw, resulting in numerous cases of angiostrongyliasis (Lv et al., 2009a, 2011; Cowie, 2013; Yang et al., 2013). Cases have also been reported in Taiwan, caused by eating raw P. canaliculata (Cowie, 2013; Tsai et al., 2013). Increasing contact with and consumption of P. canaliculata could lead to increased incidence. Thorough cooking is essential.

The empty shells of dead snails, perhaps following pesticide application, are a health hazard as they can cut the feet of people planting, harvesting or otherwise managing the crop (Cowie, 2002; Douangboupha and Khamphoukeo, 2006; Hendarsih-Suharto et al., 2006).

Poorly regulated application of dangerous pesticides can also cause human health problems (Cowie, 2002).

In Hawaii, there are cultural and lifestyle impacts. Taro is a culturally and spiritually important crop, especially for native Hawaiians, and farming taro is an important lifestyle. Taro is also important educationally, as students, teachers, and community groups use irrigated taro systems to explore topics in art, science, mathematics, health, capacity-building and Hawaiian culture. The introduction of P. canaliculata and the subsequent impacts on taro growing threaten all of these activities (Levin, 2006; Levin et al., 2006).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Capable of securing and ingesting a wide range of food
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Monoculture formation
  • Negatively impacts agriculture
  • Negatively impacts forestry
  • Negatively impacts animal health
  • Reduced amenity values
  • Threat to/ loss of endangered species
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
  • Herbivory/grazing/browsing
  • Interaction with other invasive species
  • Predation
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Highly likely to be transported internationally illegally
  • Difficult/costly to control

Uses

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Economic Value

P. canaliculata was initially introduced into Asia and Hawaii with a view to its development and sale to both local people as a food resource as well as to the gourmet restaurant trade locally and internationally. Aquaculture was actively and officially promoted in some countries (e.g. the Philippines; Naylor, 1996). In general, local people did not find it particularly tasty and it was taken up only minimally by the restaurant trade (e.g. Wada, 1997; Cheng and Kao, 2006; Preap, 2006; Wada, 2006; Yang et al., 2006; Yin et al., 2006). Nonetheless, in some regions, most notably southern China, raw P. canaliculata are considered a delicacy, but unfortunately this has resulted in people becoming infected with Angiostrongylus cantonensis, the rat lungworm; the snails were also taken to restaurants in Beijing with the same consequences, although this did prompt the Chinese authorities to take more note of the problem (MacDonald, 2006; Lv et al., 2009b; Wang et al., 2010). In the Philippines, small scale aquaculture of P. canaliculata provides fishmeal for fish, shrimp and prawn farming (Castillo and Casal, 2006). The snails are therefore of some positive economic value, although this is not without its negative consequences.

Social Benefit

In addition to its use as a food resource, P. canaliculata has also been used or recommended to a limited degree for biological control of weeds in rice paddies (Wada, 1997; Cazzaniga, 2006; Joshi et al., 2006). However, its use for this purpose is not widespread as it is a voracious feeder on rice shoots until they are a few weeks old, and as a result is a major pest of rice (Joshi and Sebastian, 2006).

Environmental Services

Apple snails in general are major components of many of the freshwater systems in which they occur naturally, including wetlands of great biodiversity value where they play key ecological roles in nutrient cycling and are key food resources for a large number of animals (e.g. Darby et al., 2002; Fellerhoff, 2002). It seems likely that P. canaliculata in particular plays such a role in many of the locations where it occurs naturally (although this aspect of its ecology has been hardly studied), especially given that it can have a major environmental impact in its non-native range (Carlsson et al., 2004a; Carlsson and Lacoursière, 2005; Carlsson and Brönmark, 2006).

Uses List

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Environmental

  • Biological control

General

  • Pet/aquarium trade
  • Research model

Human food and beverage

  • Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)

Diagnosis

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Rawlings et al. (2007) and Hayes et al. (2008, 2012) have shown that P. canaliculata can be distinguished from P. maculata, the most likely species with which it could be confused in its non-native range, by DNA sequencing. Adults of these two species can also be distinguished, though less reliably, especially by non-experts, by shell morphology and internal anatomy, notably of the penial sheath (Hayes et al., 2012). See Similarities to Other Species/Conditions for further information.

Two studies have developed rapid molecular detection protocols. However, they are only able to distinguish P. canaliculata from P. maculata (Matsukura et al., 2008) or P. canaliculata from P. maculata and P. diffusa (misidentified as P. bridgesii) (Cooke et al., 2012) and therefore could easily fail to detect one of the many other closely related species (Hayes et al., 2009a). Also, Cooke et al. (2012) considered P. maculata and P. diffusa to be non-invasive, despite P. maculata being one of the two major invasive species in Asia (Hayes et al., 2008), the USA (Rawlings et al., 2007) and Europe (López et al., 2010), and P. diffusa being the most important apple snail in the aquarium trade (Perera and Walls, 1996) and as a result transported to many parts of the world (Hayes et al., 2008), although it does not appear to have become a major pest.

Detection and Inspection

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The most recognizable sign of the presence of P. canaliculata (and other related apple snail species) is their bright-pink egg masses, which are laid on emergent vegetation (including wetland crops) and other hard surfaces above the water line, such as rocks, logs and bridge supports (Hayes et al., 2009b). These egg masses are very noticeable and can even be seen from a moving vehicle.

Similarities to Other Species/Conditions

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Species of Pomacea can be easily distinguished from those in other ampullariid genera (see figure 2 of Hayes et al., 2009a). Species in the Old World genus Pila, which also bear large, round, generally brownish or greenish dextrally coiling shells, have a brittle and calcified as opposed to a corneous and somewhat flexible operculum. Species of Lanistes, an African genus, appear to coil sinistrally, with the aperture to the left of the shell when viewed with the apex uppermost. The other Old World genera (Afropomus, Forbesopomus, Saulea) include only a small number of species and are not likely to be encountered.

Among New World genera, the three species of Marisa are readily distinguished from species of Pomacea as they are planispirally coiled (the coils are almost flat) and are thus known commonly as giant ramshorn snails. Species of Asolene are generally small < 2 cm shell height) and usually yellow with brown bands. Felipponea species are small, and unlikely to be encountered. The genus Pomella is now treated as a synonym of Pomacea (Hayes et al., 2012); the animals bear very large round shells with a relatively enormous aperture compared to other Pomacea species.

Although the shells of many Pomacea species may be extremely variable, as in P. canaliculata, the shells of some species are sufficiently characteristic that they are readily distinguished from P. canaliculata. For example, the whorls of P. scalaris, P. bridgesii and P. diffusa have a distinctive stair-like appearance, with the steps more sharply prominent in P. scalaris; the shell of P. papyracea is fragile and horny, with an almost black periostracum; and the shell of P. urceus is thick, solid, and black, with distinctive transverse ridges. Nevertheless, rather few Pomacea species can be identified definitively on the basis of the shell alone, and other morphological and molecular characters must be investigated to assist in correct identification. Also, the juveniles of many species are essentially indistinguishable morphologically.

The species with which P. canaliculata is most likely to be confused is P. maculata. The two species are extremely similar, and differences in size and subtle qualitative differences in shell shape fall within the range of individual variation, making them very difficult to distinguish morphologically (Hayes et al., 2012). However, they can be distinguished, as described by Hayes et al. (2012). P. maculata generally has a thicker shell with a more distinctive angulate shoulder; the inner apertural lip is characteristically yellow to reddish-orange, which was also noted in the original descriptions of P. insularum and P. gigas, which are now treated as synonyms of P. maculata. Differences in shell morphology are most notable in newly hatched juveniles. The number of eggs laid per clutch is substantially higher in P. maculata (average ~1500) and the individuals eggs are much smaller, so that P. canaliculata hatchlings are nearly twice as large (shell width) as those of P. maculata. The operculum of P. maculata is also much thicker and more inflexible than that of P. canaliculata, creating a much less effective seal.

The most readily apparent anatomical differences are in the male penis sheath (Hayes et al., 2012). Both species possess two glands on the dorsal surface of the penis sheath. However, the apical gland of P. canaliculata is distinguished from that of P. maculata by having both a rugose central glandular surface bordered by smoother glandular tissue. Nonetheless, the development of the two types of tissue varies with maturity and they may appear undifferentiated in younger individuals. Other species of Pomacea possess, in addition to an apical gland, both a medial and basal gland. And although both P. maculata and P. canaliculata possess two dorsal penis sheath glands, P. maculata lacks the medial gland, whereas P. canaliculata lacks the basal gland.

The two species are readily differentiated by DNA sequences (Rawlings et al., 2007; Hayes et al., 2008, 2009a, 2012).

The other Pomacea species most likely to be encountered is P. diffusa. In the past, this species has been misidentified as P. bridgesii, which is generally larger. P. diffusa is the most common ampullariid in the aquarium pet trade (Perera and Walls, 1996). It can be distinguished from P. canaliculata by its more square-shouldered whorls, as indicated above, and the fact that the suture (the junction between successive whorls) is not deeply channelled, the character that gives P. canaliculata its scientific name. Nonetheless, distinguishing these species on the basis of these shell characteristics is not easy and requires considerable experience, especially given the variability in shell shape within these species. Shell colour, the pattern of darker bands running spirally around the shell and the colour of the animal inside should not be considered diagnostic of species of Pomacea, and cannot be used to distinguish P. diffusa from P. canaliculata, especially as there are many colour varieties of P. diffusa that have been specially bred for the aquarium trade.

P.paludosa is the only North American species of Pomacea, occurring in southeastern USA and Cuba. Although its shell is coloured similarly to that of P. canaliculata and is similar in size, the suture between successive whorls is not deeply channelled, making it fairly readily distinguished, at least as adults, from P. canaliculata.

Other species that may be confused with P. canaliculata are P. lineata and P. dolioides. Both have brown shells, often with spiral bands; they are generally smaller than P. canaliculata as adults and the shells are usually thinner. They tend to have more prominent shell spires, though this character is variable in all three species, and the sutures between their whorls are not deeply channellized.

Prevention and Control

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Most of the literature on management of apple snail pests undoubtedly refers to P. canaliculata, which is the most widespread introduced species of Pomacea in Asia. However, because of the past confusion regarding the identities of the species introduced to Asia, some of the information purportedly relating to P. canaliculata may relate to either or both P. canaliculata and P. maculata.

Economic Threshold Levels

Litsinger and Estaño (1993) suggested that two or more snails per square metre represented a high damage risk, whereas fewer than two snails per square metre represented a low risk. However, the damage potential of P. canaliculata in rice depends on water depth, seedling age and pest density, in decreasing order of importance (Teo, 2003). Most farmers can judge the amount of control effort needed from their past experience. 

Prevention

Sanitary and Phytosanitary Measures

Many countries and other administrative regions have developed quarantine restrictions related to Pomacea spp. In some cases these restrictions apply to all or most species of Pomacea, because of the difficulties of distinguishing them and because little is known of the pest potential of species other than P. canaliculata and P. insularum.

Rapid Response

Eradication of invasive apple snails is only likely to be possible in the very early stages of invasion when the new infestation is highly localized. For example, when P. maculata (and perhaps P. canaliculata) were first reported in Cambodia in August 1995 (Preap et al., 2006), recommendations were made by November 2005 to eradicate them immediately, as they were only known from a suburban concrete pond and concrete back yard tanks in Phnom Penh, a clay jar in Svay Rieng and from a few small ponds in Prey Veng (Cowie, 1995a; Preap et al., 2006). They could have been eradicated entirely at that time but other than destroying the snails in the clay pot, no action was taken and they subsequently spread to at least ten provinces (Preap et al., 2006). In Vietnam it took only five years from initial introduction for Pomacea spp. (probably both P. canaliculata and P. maculata; Hayes et al., 2008) to be present in every rice-growing province of the country (Naylor, 1996). Rapid response is therefore crucial.

Public Awareness

In the early days of invasion of Asia by Pomacea spp. there was little awareness of the problems the snails could cause and therefore considerable efforts were made to promote their aquaculture, for example in the Philippines (Naylor, 1996). There was little awareness in some uninfested countries of the problems caused in countries with serious infestations. For example, when apple snails were first discovered in Cambodia (Cowie, 1995a) there was apparently no public awareness of the major problems they were already causing in neighbouring Vietnam. Raising public awareness is not only important to prevent the further spread of Pomacea species in Asia and elsewhere (e.g. USA, Europe), but also to warn people in regions in which parasites such as Angiostrongylus cantonensis occur of the dangers of infection.

Eradication

Eradication of invasive snails is in general extremely difficult (Cowie, 2011). Eradication of a new infestation of the native Asian apple snail Pila conica was accomplished in Palau by manually collecting the snails from the infested pond, which was then covered with a layer of oil; the pond probably also was infested with a species of Pomacea, probably P. canaliculata, as pink egg masses were reported (Cowie, 2002). This is the only report of eradication of any apple snail species and was only possible because a very small area (a single pond) was infested.

Control

Although many of the following measures reduce snail numbers, at least to some extent, their impacts on yield losses are much less rigorously documented.

Cultural and physical/mechanical control and sanitary measures

Several cultural methods are very effective at minimizing snail damage. The most often used in rice cultivation are methods of crop establishment, seeding rate and water management. The following details are derived primarily from FAO (1989), Litsinger and Estaño (1993), Halwart (1994a), Cowie (2002) and Joshi and Sebastian (2006) unless otherwise indicated. Levin (2006) detailed the various methods used in taro farming in Hawaii.

Ploughing and harrowing during the off-season increase the mortality of dormant snails in the soil. Therefore land preparation for a non-rice crop in the off-season decreases the snail population, particularly if the community carries it out. Flooding the land before planting revives dormant snails, which are then crushed by mechanized land preparation carried out by hydrotiller. Other control methods include levelling the field to facilitate drainage and to remove small refuges used by the snails. Planting crops at high densities, burning straw and planting on ridges above the water line also control the numbers of snails.

Choosing a suitable planting method is very important to minimize damage. The objective is to prevent older snails feeding on young plants. Transplanting is therefore preferable to direct seeding because the seedlings are older and more resistant to the snails. Using a well-drained location can protect the seedbed. The traditional method is to sow seedlings in a wetbed seedling nursery and then transplant them when they are 3-4 weeks old. Farmers in Laguna, Philippines, have adopted the dapog method, in which the seeds are sown on banana leaves rather than on soil; this reduces the labour involved in pulling the seedlings. The seedlings are 9-14 days old when they are transplanted in hills (a handful of seedlings). Farmers are now adopting direct sowing of pre-germinated seedlings because no seedbed is used and the method is inexpensive.

A direct-seeded crop is vulnerable for 4 weeks after establishment; a transplanted dapog crop is vulnerable for 3 weeks, and wetbed seedlings are vulnerable for 2 weeks. A transplanted crop should be established with seedlings that are 4-5 weeks old to reduce the time in the field (Mochida, 1991; Litsinger and Estaño, 1993; Halwart, 1994a; Schnorbach, 1995; Naylor, 1996). Older seedlings reduce the time in the field during the most vulnerable stage. The crop is vulnerable until the tillers stop elongating, because during this phase of active growth, little silica is deposited and the tissues offer little resistance to the rasping feeding action of a snail’s radula. Four weeks after emergence, the plants are difficult for the snails to rasp because silica has hardened the culms. Snails 1.5 cm in diameter can feed on young plants up to 4 weeks of age and 6.5 cm diameter snails can feed on 9-week-old plants.

Higher seeding rates provide greater tolerance to damage because missing patches can be filled in (Halwart, 1994a; Cowie, 2002). Extra seedlings, maintained along the borders of the field, can be used to replant voids.

Lowering the water level or draining the paddy will not kill the snails because they are able to survive long periods without water. However, snails move only in standing water and are immobile if the water depth is less than half of their shell height. Periodic draining of the fields to a depth of 1 cm is a very effective control practice because it prevents the snails moving and feeding (Yamanaka et al., 1988; Wada, 1997, 2004). The field should be well levelled and maintained at saturation, minimizing the time it contains standing water. Farmers with their own pumps can manage water levels better than those served by large irrigation systems.

In some areas of the Philippines, farmers' traditional practice of crop husbandry is to apply basal soil complete fertilizer (60:40:40 kg/ha of N, P and K, respectively) combined with urea at the final harrowing and levelling. This practice resulted in the apple snails becoming inactive and half of them died. The dead apple snails in fertilizer-treated plots had open opercula whereas those in molluscicide-treated fields had closed opercula. However, in a single element and commercial organic fertilizer trial, no apple snail mortality was observed. It was concluded that the combination of three elements (N, P and K) caused the mortality (Cruz et al., 2001).

The feeding preferences of P. canaliculata for different plants can be explored to divert them from feeding on young rice seedlings. The snails show higher preferences for certain fruits and vegetables, such as melons, watermelons, lettuce, aubergines and tomatoes, than for rice seedlings (Fukushima et al., 2001), although provision of additional food sources may serve to enhance the snail populations. Likewise, these plants can be used to collect the snails and facilitate easy hand picking (Cagauan and Joshi, 2003). In areas where plant attractant materials are scarce, old newspapers can be used to attract apple snails in rice fields before crop establishment (direct sowing or transplanting), and in fields where rice crops have already been established, taro and papaya leaves are the best attractants (Joshi and Cruz, 2001).

Hand picking of snails and removal of egg masses is a widespread control method and is relatively effective, especially on a small scale, but extremely time consuming (FAO, 1989; Cowie, 2002; Levin, 2006; Levin et al., 2006; Hendarsih-Suharto et al. 2006). Hand collection is best done in the morning or late afternoon when the snails are most active. A mechanical device called an egg clapper has been developed to enable farmers to crush egg masses without stooping over (Awadhwal and Quick, 1991). Destruction of eggs can be facilitated by placing stakes in the paddy on which the snails oviposit; stakes with eggs are then readily removed (Cowie, 2002). Wire or bamboo screens can be placed across field irrigation inlets to trap snails moving between fields (Cowie, 2002). This procedure has been widely used in taro farms in Hawaii (Levin et al., 2006). Farmers can facilitate collection by making shallow canals around the edges of their fields, for example by dragging a large rock behind a draft animal; the snails collect in the canals and are easily removed, or can be treated more effectively with localized pesticides, should this be considered appropriate (Cowie, 2002; Levin, 2006; Levin et al., 2006). The use of baits has been suggested as a means of getting the snails to congregate, thereby making them easier to collect. Lettuce, cassava leaves, sweet potato leaves, taro leaves and papaya leaves have been suggested, but baits have to be significantly more attractive to the snails than the crop is, and it is possible that providing additional food as baits would enhance snail numbers (Cowie, 2002). Collected snails can be crushed and fed to ducks; indeed, where duck farming is popular there is a market for the snails as duck food, and collecting them provides employment for landless labourers.

The edges, dikes or bunds that surround the rice paddies, taro patches, etc. should be neatly maintained. This reduces egg-laying sites and allows snails to be more easily seen and destroyed. It may also decrease the chances of snails moving between paddies (Cowie, 2002).

In Japan, physical control of P. canaliculata by rotary cultivator is efficient as it decreases their density (Takahashi et al., 2002a). In submerged direct sowing, 48.1% of the area was damaged by P. canaliculata, while in a rotary cultivation field it was 2.3% (Takahashi et al., 2002b). See also Wada (2004).

Crop rotation between rice and a dryland crop has been investigated in Japan with some success, the usual crop being soybean (Wada, 2004; Wada et al., 2004). In Hawaii, leaving taro fields fallow and dry for at least a year is an effective control measure but results in economic losses because the land is not productive (Levin, 2006).

Biological Control

None of the predators of apple snails in their native ranges have been shown to play a significant role in snail population regulation, although snail kites may be important in this regard (R.H. Cowie, personal observations). In South-east Asia, various fish, birds, rats, lizards, frogs, toads, beetles and ants are known to feed on introduced apple snails or their eggs (Halwart, 1994a). Some of these, especially rats, also cause serious damage to rice, and introduction or promotion of others as biocontrol agents may have unknown environmental consequences. Only ducks and fish have attracted any serious consideration as potential control agents.

Rice farmers often breed ducks and herd them into rice fields to eat the snails in the period before transplanting (Cowie, 2002; Wada, 2004). A similar approach has been taken for taro in Hawaii (Levin, 2006; Levin et al., 2006). Various duck varieties have been used (Teo, 2001; Levin, 2006; Levin et al., 2006). Two to four ducks per 100 m² were effective in controlling young snails (Vega 1991; Pantua et al., 1992; Rosales and Sagun, 1997; Cagauan, 1999), but some farmers reject this practice because duck faeces contain fluke cercariae that penetrate the skin, which results in itchiness or paddy-field dermatitis (Cagauan and Joshi, 2003). A density of 5-10 ducks per ha in continuous grazing for a period of 1-2 months significantly reduces the pest density from 5 snails per m² to < 1 snail per m² (Cagauan, 1999). As ducks graze on and otherwise damage young rice seedlings, it is appropriate to release the ducks when the transplanted seedlings are 4 weeks old. For direct-sown rice, a longer waiting period of 6 weeks is necessary. Using ducks for control may be more effective against P. canaliculata than using chemical molluscicides because the chemicals become ineffective either due to poor drainage in the plots or because snails are still buried in the soil (Cruz and Joshi, 2001).

Fish have also been suggested as biological control (Rondon and Sumangil, 1989; Morallo-Rejesus et al., 1990), but few quantified studies have been undertaken (Cagauan and Joshi, 2003). Cyprinus carpio (common carp) and Oreochromis niloticus (Nile tilapia) are popular species for controlling P. canaliculata, with the former more effective than the latter in removing snails (Halwart, 1994b). C. carpio crack the snail's shell, ingest the soft tissue and spit out the broken shell; thus they can feed on snails up to 12 mm high. In contrast, O. niloticus ingests the whole shell, and can therefore only feed on snails smaller than 3 mm. In Japan, black or Chinese carp (Mylopharyagodon piceus) and C. carpio fingerlings have been released to feed on newly hatched snails (Mochida et al., 1991). Models predicting predation rates are provided by Yusa et al. (2001), Ichinose and Tochihara (2001) and Ichinose et al. (2002). One of the problems with using fish is that the water must be kept deep enough for them, which may not be compatible with other methods (Wada, 2004).

Little is known of microorganisms associated with ampullariids that might be useful in control, nor of parasitoids that attack either the snails or their eggs. In the Philippines, twelve bacterial isolates were tested, seven of which were effective against P. canaliculata (Cowie, 2002).

Halwart (1994a) recommended that specific natural enemies for P. canaliculata, such as the predatory Sciomyzidae, should be sought in its native home in South America.

All deliberate introductions of non-indigenous species, including as biological control agents, should be carefully evaluated prior to introduction in terms of both their positive and negative potential impacts, and monitored after introduction.

Chemical Control

Several of the molluscicides that have been used against P. canaliculata, such as organotin compounds, copper sulfate, calcium cyanamide and sodium pentachlorphenolate, pose great environmental risks. A number of insecticides have been used against snails, for example isapophos, cartap and bensultap. Dipping seedlings in cartap or bensultap before planting gave protection against P. canaliculata for 2 weeks (Asaka and Sato, 1987). Use of the most toxic products has been prohibited in many countries for some time (Cowie, 2002; Schnorbach et al., 2006), but many chemicals are still used illegally.

The problem with molluscicides applied as sprays or dips is that rain readily washes them away, making reapplication necessary. In Japan (Wada et al., 2001), pellets have performed well under wet conditions because they are formulated to withstand submergence. One or two applications of granular iprobenfos (IBP) after sowing suppressed damage at low snail density and in light rain. However, damage to rice occurred in heavy rain even with two IBP applications. The mortality of snails in the IBP-treated fields varied from 0 to 69%, probably depending on the rain. In Kyushu, however, IBP application is impractical in direct-sown rice fields because it often rains heavily in the sowing season (Wada et al., 2001). Furthermore, in any pesticide treatment directed at the snails in the water, even if the snails are killed, eggs laid above water will not be affected and will go on to hatch after the pesticide has dissipated. A second application, perhaps a month after the first, is then necessary to kill the newly hatched snails before they grow to reproductive maturity (Cowie, 2002).

In Japan, a metaldehyde molluscicide pelleted bait (usually wheat bran) has been developed (Cheng, 1989; Mochida et al., 1991; Wada, 2004). An application of metaldehyde pellets after sowing successfully suppressed damage to rice by apple snails, when used in conjunction with 13 or 18 days' drainage after sowing in both light and heavy rain. About 90% of snails were killed by the application of metaldehyde (Wada et al., 2001). In a related field experiment, 10-day drainage immediately following the wet seeding and subsequent 11-day low-level water management successfully suppressed snail damage to an acceptable injury level when metaldehyde granules were applied, 4 and 10 days after sowing. The analysis of the results of metaldehyde application revealed that the success was due mainly to its effect as a feeding arrestant (Suzuki et al., 2000; Schnorbach et al., 2006). However, pelleted baits are relatively expensive, although the whole field seldom needs to be treated because the snails aggregate in the lower areas. Metaldehyde is rendered ineffective when the water temperature falls below 10°C, so it is appropriate for use in the tropics (Cheng, 1989). Its value in temperate Taiwan, Korea and Japan, however, is limited because transplanting is carried out in the cool spring.

The quick knock-down effect of the pesticides applied directly on apple snails makes this method quite popular with farmers (Alba et al., 1993; Cruz et al., 2000; Cruz and Joshi, 2001), but the efficacy of all commercial molluscicide formulations lasts up to 3 days (Cruz et al., 2000). Farmers are not often aware of the adverse effects of pesticides on non-destructive native snail species and other non-target organisms, and do not always consider health or environmental effects in choice of pesticides or control options (Rice IPM Network, 1991; Cagauan and Joshi, 2003). Educational campaigns are therefore needed to make farmers aware of these adverse effects (Cruz et al., 2000).

A number of plants have been shown to have molluscicidal properties, but they are not long lasting and some are toxic to fish (Agaceta et al., 1981; Cheng, 1989; Morallo-Rejesus et al., 1990; Alba et al., 1993; Banoc and Noriel, 1991; Lobo et. al., 1992; Maini and Morallo-Rejesus, 1993; Arthur et al., 1996) and have equally serious environmental and human health effects as synthetic pesticides, especially if deployed persistently over wide areas and in high concentrations (Taylor et al., 1996).

Host Resistance

No rice cultivars are resistant to P. canaliculata feeding, but modern high-tillering plant types are those most able to compensate for the damage. Feeding preferences were observed under no-choice and free-choice conditions in trials of rice varieties carried out by the Philippine Seed Board (PSBRc) (Cruz et al., 2002).

IPM

No single tactic is superior to a combination of various approaches for P. canaliculata control (Rice IPM Network, 1991; Cagauan and Joshi, 2003; Litsinger and Estaño, 1993; Cowie, 2002; Levin, 2006). In rice, hand picking has been the most widely practised method for controlling the snails, followed by chemicals and the use of older seedlings (Rice IPM Network, 1991). With taro in Hawaii, the most effective combination includes fallow periods with cover crops, dry-downs and trenching, and biological control with ducks (Levin, 2006); no pesticides are authorized for use, although some have been used illegally (R.H. Cowie, personal observations). Undoubtedly a combination of methods is most effective but rigorous quantitative assessments of this kind of integrated pest management approach are few (Litsinger and Estaño, 1993).

In most Asian countries, P. canaliculata, although introduced for food, has not been generally liked and so control by promotion of its use is not likely to succeed (Ichinose et al., 2001). Using a molluscicide alone requires high application rates, which most farmers cannot afford. Litsinger and Estaño (1993) therefore tested combinations of cultural and chemical methods. A crop transplanted with wetbed seedlings under low-risk snail densities (two snails per square metre) can be protected either by transplanting older seedlings (4 weeks old) or using periodic drainage. Under high-risk snail densities (more than two snails per square metre), a combination of two of the following methods (using older seedlings, water management, or removing snails manually) was sufficient. If the crop is established by direct seeding or dapog under low-risk snail densities, the crop requires water management and removing the snails by hand. Under high-risk conditions (dapog seedlings or direct seeding) the crop requires three control methods (using older seedlings, water management and removing snails by hand).

In the Philippines, increasing seedling age at planting from 2 to 5 weeks resulted in significant reductions in snail damage in terms of missing hills. Increasing seedling number per hill, to 8, 6, 4 and 2 for 2-, 3-, 4-, and 5-week-old seedlings, respectively, also reduced snail damage. In a snail-free experiment, grain yield was not affected significantly when seedling age increased from 2 to 5 weeks (Sanico et al., 2002). Chemical control can be substituted for any of the non-chemical control methods and when used in combination with them, the application rate can be reduced by half.

It is not possible to make blanket recommendations regarding IPM of P. canaliculata. Situations differ from country to country, within countries and among specific locations, and different practices are favoured in different places. IPM strategies involving both existing control measures and measures developed in the future will differ from region to region, depending on the levels of infestation, potential environmental consequences, the specific needs of the local farmers and the options open to them, and the local economy.

Gaps in Knowledge/Research Needs

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The following are just a few of the many questions that could be answered by additional research.

Pest Identity

Although it has become possible to distinguish P. canaliculata from some of its congeners reliably, many of the older records did not distinguish P. canaliculata from the other major invasive Pomacea species in Asia, P.maculata, or identify them incorrectly. The specific distributions of the two species in Asia therefore remain poorly known in most countries, with the exceptions of China, the Philippines, Taiwan and perhaps Japan.

Reasons for Invasiveness

Comparative studies of other as yet non-invasive species of Pomacea, within a phylogenetic framework, would be valuable for understanding why P. canaliculata and P. maculata have become so invasive and whether any other Pomacea species could become invasive in the future.

Differences between P. canaliculata and P. maculata

P. maculata seems as yet to be less widespread in Asia than P. canaliculata. There are also hints that P. maculata may be less of a problem than P. canaliculata; for example, only P. maculata has been definitively recorded in Cambodia, and the snails appear to cause fewer problems in that country than in many others. Studies of the ecology and behaviour of the two species could help to address these possible differences between the two species.

Yield Loss

Although there are many estimates of areas of arable land infested, and some estimates of economic costs of control measures, there are rather few detailed assessments of crop yield losses.

Impact on Native Biodiversity

With the exception of a few experimental studies and anecdotal observations, little is known of the impacts of either P. canaliculata or P. maculata on native biodiversity in the regions they have invaded.

References

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Links to Websites

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The Apple Snail (Ampullariidae) Websitehttp://applesnail.net/

Contributors

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06/09/13 Reviewed by:

Rob Cowie, University of Hawaii, USA

15/12/03 Reviewd by:

Ravi Joshi, Philippine Rice Research Institute, Philippines

30/04/96 Original text by:

James Litsinger, Consultant, USA

 

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