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Datasheet

Sepedon aenescens
(snail-killing fly)

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Datasheet

Sepedon aenescens (snail-killing fly)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Host Animal
  • Preferred Scientific Name
  • Sepedon aenescens
  • Preferred Common Name
  • snail-killing fly
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • Sepedon aenescens is a species of marsh fly, otherwise known as a snail-killing fly. It has blueish-black metallic colouration and can grow up to about 8 mm in length. It has a primarily Oriental distribution t...

  • Principal Source
  • Draft datasheet under review

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Pictures

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PictureTitleCaptionCopyright
Sepedon aenescens (snail-killing fly); a dipteran (Diptera; Sciomyzidae) predator of limnaeid snails. The aquatic larvae are predators of non-operculate snails.
TitleAdult
CaptionSepedon aenescens (snail-killing fly); a dipteran (Diptera; Sciomyzidae) predator of limnaeid snails. The aquatic larvae are predators of non-operculate snails.
Copyright©Show ryu, Japan-2010/via wikipedia - CC BY-SA 3.0
Sepedon aenescens (snail-killing fly); a dipteran (Diptera; Sciomyzidae) predator of limnaeid snails. The aquatic larvae are predators of non-operculate snails.
AdultSepedon aenescens (snail-killing fly); a dipteran (Diptera; Sciomyzidae) predator of limnaeid snails. The aquatic larvae are predators of non-operculate snails.©Show ryu, Japan-2010/via wikipedia - CC BY-SA 3.0

Identity

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Preferred Scientific Name

  • Sepedon aenescens Wiedmann, 1830

Preferred Common Name

  • snail-killing fly

Other Scientific Names

  • Sepedon sauteri Hendel, 1911
  • Sepedon sinensis Mayer, 1953
  • Sepedon violacea Hendel, 1909

International Common Names

  • English: marsh fly; snail-killing fly; swale fly

Summary of Invasiveness

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Sepedon aenescens is a species of marsh fly, otherwise known as a snail-killing fly. It has blueish-black metallic colouration and can grow up to about 8 mm in length. It has a primarily Oriental distribution that extends in the north-east into the Palaearctic region. S. aenescens is common in Asian paddy fields and surrounding freshwater marshes, ponds and creeks, where the larval prey snail reside. First introduced from Japan to Hawaii in 1966 as a biological control agent of the lymnaeid snail vectors of the liver fluke Fasciola gigantica, S. aenescens became well established on the major Hawaiian Islands. Attempts to introduce S. aenescens into southern California, USA, to control Fasciolagigantica were unsuccessful. Concern has been raised about the non-target effects of introduced sciomyzids on native lymnaeid species of snails in Hawaii. Together with habitat loss, predation by S. aenescens and another introduced sciomyzid, S. macropus, represents a significant threat to the survival of native Hawaiian lymnaeid snails, including the threatened Newcomb’s snail (Erinna newcombi).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Diptera
  •                         Family: Sciomyzidae
  •                             Genus: Sepedon
  •                                 Species: Sepedon aenescens

Notes on Taxonomy and Nomenclature

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Sepedon aenescens Wiedemann, 1830, belongs to the dipterous marsh fly/snail-killing fly family Sciomyzidae (Barker et al., 2004; Knutson and Vala, 2011). It was first described by Christian Rudolph Wilhelm Wiedemann from specimens collected in China. Species of Sepedon in the Oriental region have had a confused taxonomic history and south-west Asian populations were identified by some taxonomists as Sepedon sphegea (Fabricius, 1775) and by others as S. aenescens Wiedemann, 1830, Sepedon violacea Hendel, 1909, Sepedon sauteri Hendel, 1911, or Sepedon sinensis Mayer, 1953 (Knutson and Orth, 1984). It was concluded that Oriental populations should be known as S. aenescens, with S. violacea, S. sauteri and S. sinensis as synonyms (Knutson, 1977). The sibling species S. aenescens and S. sphegea were placed in the S. sphegea complex, together with a new species, S. femorata s. nov., from Spain and southern France (Knutson and Orth, 1984). S. aenescens and S. sphegea are almost completely allopatric: S. sphegea has a pan-Palaearctic distribution, while S. aenescens has a primarily Oriental distribution that extends in the north-east into the Palaearctic. S. femorata has an area of sympatry with S. sphegea in southern France. Knutson (1977) and Beaver et al. (1977) erroneously listed S. imbuta as a synonym of S. aenescens.

Eight genera are recognized in the Sepedon group: Ethiolimnia Verbeke, Teutoniomyia Hennig, Thecomyia Perty, Sepedoninus Verbeke, Sepedonella Verbeke, Sepedon Latreille, Sepedomerus Steyskal and Sepedonea Steyskal (Marinoni and Mathis, 2006).

Description

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The life stages of S. aenescens are the egg, three larval instars, a puparium and the adult. Adults of S. aenescens have a bluish-black head and thorax (Knutson and Orth, 1984). The body length of the male ranges from 6.2-8.1 mm and that of the female from 6.4-8.2 mm (Sueyoshi, 2001). There is some variation in body colour, especially in the extent of a metallic sheen or a whitish tomentum on the thorax and abdomen, and this variation may have led to confusion in taxonomy and to Hendel (1909, 1911) and Mayer (1953) naming segregates of S. aenescens as new species. The wings and legs also show some variation in pigmentation (Knutson and Orth, 1984). In the Malaysian region the legs are yellow (Englund et al., 2003). The wing length of the male ranges from 6.0-7.0 mm and that of the female from 5.8-7.4 mm (Sueyoshi, 2001). The male genitalia are described in detail by Knutson and Orth (1984).

The eggs of S. aenescens (as S. sauteri) are described in Nagatomi and Tanaka (1967). The immature stages of S. aenescens have not been described (Knutson and Vala, 2011).

Distribution

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S. aenescens has been recorded from China, Hong Kong, Taiwan, Japan, Ryukyus, South Korea, Philippines, Thailand, Nepal, India, Bangladesh, Pakistan, Afghanistan and Russian Far East (Yano, 1978; Barnes and Knutson, 1989; Knutson and Orth, 1984; Lindsay et al., 2009; Rozkošný et al., 2010).

It has high population densities in Japan, the Ryukyus and Taiwan. In Japan, it is more abundant in the western part than the north-eastern part and it is common in Hokkaido, Akita, Nagano, Gifu (Yano, 1978).

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

AfghanistanPresentKnutson and Orth, 1984
BangladeshPresentYano, 1978As Sepdon sauteri
ChinaPresentYano, 1978As Sepedon sauteri
-FujianPresentKnutson and Orth, 1984
-HenanPresent
-Hong KongPresentYano, 1978; Knutson and Orth, 1984
-HunanPresentKnutson and Orth, 1984
-JiangsuPresentKnutson and Orth, 1984
-SichuanPresentKnutson and Orth, 1984
-YunnanPresentKnutson and Orth, 1984
-ZhejiangPresentKnutson and Orth, 1984
IndiaPresentPresent based on regional distribution.
-DelhiPresentKnutson and Orth, 1984
-Himachal PradeshPresentKnutson and Orth, 1984
-Indian PunjabPresentKnutson and Orth, 1984
-KarnatakaPresentKnutson and Orth, 1984
-MeghalayaPresentKnutson and Orth, 1984
-OdishaPresentKnutson and Orth, 1984
-RajasthanPresentKnutson and Orth, 1984
-Uttar PradeshPresentKnutson and Orth, 1984
-West BengalPresentKnutson and Orth, 1984
IndonesiaPresentPresent based on regional distribution.
-SumatraPresentKnutson and Ghorpade, 2004
JapanPresentNagatomi and Kushigemachi, 1965; Yano, 1978; Knutson and Orth, 1984
-HokkaidoPresentYano, 1978; Sueyoshi, 2001
-HonshuPresentYano, 1978; Sueyoshi, 2001
-KyushuPresentYano, 1978; Sueyoshi, 2001
-Ryukyu ArchipelagoPresentYano, 1978; Sueyoshi, 2001
-ShikokuPresentSueyoshi, 2001
Korea, DPRPresentRozkošný et al., 2010
Korea, Republic ofPresentKnutson and Orth, 1984; Rozkošný et al., 2010; Cho et al., 2011; Lim et al., 2012; Park et al., 2012Gadeok-do, Daebudo and Yeongheungdo
NepalPresentYano, 1978; Knutson and Orth, 1984
PakistanPresentYano, 1978; Knutson and Orth, 1984
PhilippinesPresentYano, 1978; Knutson and Orth, 1984; Knutson and Ghorpade, 2004
TaiwanPresentYano, 1978; Knutson and Orth, 1984
ThailandPresentYano, 1978; Knutson and Orth, 1984; Knutson and Ghorpade, 2004

North America

USAPresentPresent based on regional distribution.
-CaliforniaAbsent, formerly presentIntroduced1975 Not invasive Knutson and Orth, 1984Released in southern California but didn’t become established
-HawaiiPresentIntroduced1966 Invasive Davis and Krauss, 1967Became established on the major Hawaiian islands

Europe

Russian FederationPresentPresent based on regional distribution.
-Russian Far EastPresentKnutson and Orth, 1984

History of Introduction and Spread

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Eleven species of Sciomyzidae, including S. aenescens, have been introduced to Hawaii, USA, in attempts to find biological control agents of the snail vectors of the liver fluke, Fasciola gigantica (Davis, 1974; Barker et al., 2004). The liver fluke has been recorded in the Hawaiian Islands since 1892 and is the causative agent of fascioliasis, one of the most important parasitic diseases of beef and dairy cattle there (Davis, 1960).

S. aenescens was introduced from Fukuoka, Kyushu, Japan, and was released on the major Hawaiian islands between 1966 and 1968 (Davis and Krauss, 1967; Davis and Chong, 1968; Knutson and Vala, 2011). S. aenescens became established as early as the same year of release (Davis and Chong, 1968, 1969). Further releases were made using flies from Nagoya, Japan, on Kauai in 1971 (Davis, 1972). S. aenescens was collected on Maui in 2003 (Englund et al., 2003).

Releases of adults of S. aenescens (reared from eggs imported from Hawaii) were also made in Riverside, southern California, in August 1975 for the control of lymnaeid vectors of Fasciola gigantica, where the most common snail was Physa virgata Gould (Knutson and Orth, 1984). Establishment was unsuccessful as the fly was not recovered later in the year of release. Knutson and Orth (1984) suggest that biological control in southern California may have been more successful by employing the sibling species S. sphegea from the middle of its Mediterranean range, rather than S. asenescens from the margins of its range (Japan).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
California Hawaii 1975 Biological control (pathway cause) No No Knutson and Orth (1984) Introduced in an attempt to control lymnaeid snail vectors of liver fluke (Fasciola gigantica)
Hawaii Japan 1966-71 Biological control (pathway cause) Yes No Davis (1972); Davis and Chong (1969); Davis and Krauss (1967) Introduced in an attempt to control lymnaeid snail vectors of liver fluke (Fasciola gigantica)

Habitat

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S. aenescens is common in Asian paddy fields and surrounding freshwater marshes, ponds and creeks, where the larval prey snails reside (Beaver et al., 1977; Yano, 1978). In field studies in Fujian Province, China, the adults were observed resting on vegetation such as grasses, sedges, water weeds, rapeseed and wheat plants growing near to creeks, streams and ponds during the spring. The larvae were observed to feed on Lymnaea swinhoei in the marshes, small ponds or narrow grassy creeks. When the rice was planted in late summer, the adults left the wheat and flew to the rice fields where they rested and oviposited on the lower parts of the stems. The larvae fed on the snail Lymnaea parva, which is abundant in the paddy fields (Fan et al., 1993).

Habitat List

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CategoryHabitatPresenceStatus
Freshwater
Ponds Principal habitat Natural
Rivers / streams Principal habitat Natural
Terrestrial-natural/semi-natural
Wetlands Principal habitat Natural

Host Animals

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Animal nameContextLife stageSystem
Biomphalaria
Physa acuta

Biology and Ecology

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Reproductive Biology

Most adults of Sciomyzidae mate within 1-15 days after emergence from the puparia, usually within about one day (Knutson and Vala, 2011). In S. aenescens the male produces a secretion, either anally or orally, which is presented to the female as a nuptial ‘gift’. The female consumes this secretion during copulation (Berg and Valley, 1985; Knutson and Vala, 2011).

S. aenescens has been reported to lay 1-37 eggs in masses on leaves of rice and other plants (Nagatomi and Kushigemachi, 1965, cited in Knutson and Vala, 2011). In studies in Fujian Province, China, S. aenescens generally laid a batch of 20-30 eggs (Fan et al., 1993). In laboratory studies, Beaver et al. (1977) reported that the eggs were laid in neat rows on grasses provided in rearing jars or on the walls of the jars.

Life Stages

The ranges, means and standard deviations of the life stages of S. aenescens are reported in Beaver et al. (1977). The mean times (temperature not given) were 2.65 days for incubation, 3.03, 3.48 and 3.46 days for the three larval stages, 5.31 days for the puparial period and 14.50 days for preoviposition period. Nagatomi and Kushigemachi (1965) reported a larval duration of 7-11 days, a pupal period of 4-8 days and a total period from emergence to puparium formation of 14-21 days (Knutson and Orth, 1984). Yoneda (1981) gave the following mean development times for S. aenescens reared on Hippeutis (Segnitilia) cantori at 25°C in Japan: 4.0 days for incubation, 9.0 days for the larval stage, 6.0 days for the puparial period, making a mean total of 19.0 days. Fan et al. (1993) reported that oviposition to adult emergence averaged about 20 days at a mean temperature of 26°C and about 13 days at 32°C.

Physiology andPhenology

Adults of Sepedon are active in all except near-freezing weather. S. aenescens belongs to phenological Group 2: multivoltine species overwintering as adults. They undergo reproductive diapause during the winter in Fukuoka, Japan, with poorly developed ovaries and small and narrow ovarioles, but unusually for insects in imaginal diapause the fat bodies are not well developed and the flies are active and feed on warm days (Nagatomi and Kushigemachi, 1965; Channa Basavanna and Yano, 1969, cited in Knutson and Vala, 2011). In Chiang Mai, Thailand, the flight period was from June to November in 1971 and from the middle of July to December in 1972. A few adults were collected in April in Chiang Mai. In some parts of the geographical range of the species, adults were collected all year (Beaver et al., 1977).

Longevity

In studies in Fujian Province, China, Fan et al. (1993) reported that the adult lived for 2 months in the laboratory in spring, and 40-50 days in the summer.

Nutrition

The larvae of S. aenescens are aquatic predators of non-operculate snails (Knutson and Vala, 2011, p. 312). In nature, they have been observed preying on Gyraulus hiemantium in Japan (Nagatomi and Kushigemachi, 1965, cited in Knutson and Vala, 2011), Lymnaea ollula in Japan (Yano, 1978), and Lymnaea swinhoei and Lymnaea parva in China (Fan et al., 1993). In laboratory rearings, larvae killed all non-operculate snails provided and more than one larva would often attack the same snail (Beaver et al., 1997). Yoneda (1981) reported the following non-operculate species as prey to the larvae of S. aenescens: Austropeplea ollula, Radix auricularia japonica, Physa acuta [Physella acuta], Hippeutis (Segnitilia) cantori, Gyraulus chinensis, Biomphalaria sp. and Bulinus sp. Two operculate species, Oncomelania nosophora and Parafossarulus manchouricus, were not attacked by larvae because their operculum was too rigid but S. aenescens can feed on crushed operculate snails in laboratory rearings (Beaver et al., 1977).

In field studies in Fujian Province, China, larvae of S. aenescens killed one Lymnaea snail a day on average, depending on the larval stage and host size (Fan et al., 1993).

The food of adults and how adult sciomyzids feed is poorly known. The adults of Sciomyzidae are known to feed on decaying animal matter (Barker et al., 2004). In nature, the adults would be able to feed on snails killed but not entirely consumed by the larvae. Adults of S. aenescens have been observed feeding on a dead earthworm on a rice leaf in Thailand (Yano, 1978). In laboratory studies, adults of Sepedon are able to survive for several weeks by feeding on a diet of honey and brewer’s yeast, but for full egg production a protein supplement is required (Knutson and Vala, 2011). With Sepedon sinipes, McDonnell et al. (2005) found best adult longevity and fecundity from a mixed diet of honey/yeast and crushed snails.

Feeding Behaviour

The larva attacks the snail by piercing the exposed foot with its mouthhooks. The snail retracts into its shell and either pulls the larva in with it or the larva follows in quickly. Death of the snail occurs by bleeding and this can take up to an hour for a large snail, depending on the extent of the opening in the haemocoel. The larva feeds rapidly, ingesting haemolymph and bits of snail flesh. The larva leaves when it has had sufficient food and will kill another snail when it is hungry again (Neff and Berg, 1966).

Environmental Requirements

Yoneda (1981) carried out laboratory experiments to determine the effect of rearing temperatures on the development and predation of S. aenescens reared on Hippeutis (Segnitilia) cantori or Physella acuta. The theoretical temperature thresholds for development were 13.5°C for the egg stage, 8.0°C for the larval stage, 11.1°C for the pupal stage, and 10.3°C for the whole immature period (egg to emergence), and the thermal constants for each of these developmental stages were an average of 36, 160, 78 and 268 day degrees, respectively. The survival rates from larval stage to adult were lower at 15°C (61.5%) and 30°C (60.0% or 69.2% when reared on Physella acuta or Hippeutis (Segnitilia) cantori, respectively) than at intermediate temperatures (88-100%). The male:female ratio was biased in favour of males at low temperatures (1.7:1 at 15°C and 1.4:1 at 19°C when reared on Physella acuta) and in favour of females at 30°C (1:2 when reared on Physella acuta and 1:2.6 when reared on Hippeutis (Segnitilia) cantori).

Pupal weights of larvae reared at 15°C and 30°C were lighter than those reared at intermediate temperatures (19, 22 and 25°C), but there was no difference between pupal body length or width between the different rearing temperatures. The average length of adult forewing was shortest at 30°C (6.1 mm) and longest at 19°C (6.9 mm) (Yoneda, 1981).

The duration of development of each of the development stages of S. aenescens is tabulated in Yoneda (1981). There was no significant difference in the larval development times when fed on Physella acuta compared with Hippeutis (Segnitilia) cantori at 25°C (mean of 9.6 and 9.0 days, respectively), but the latter was attacked more easily. The total numbers of snails eaten by larvae were greater at 15°C and 19°C (average of 34.7 and 27.1, respectively) and 30°C (average of 23.3) than at intermediate temperatures (22°C and 25°C; average of 13.0-16.5), while the number of snails consumed per day was greatest at 30°C (2.7 for Physella acuta and 3.3 for Hippeutis (Segnitilia) cantori compared with 1.4-1.8 at 15, 19, 22 and 25°C.

Natural Food Sources

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Food SourceLife StageContribution to Total Food Intake (%)Details
Austropeplea ollula Larval
Biomphalaria sp. Larval
Bulinus sp. Larval
Larval
Larval
Larval
Gyraulus hiemantium Larval
Hippeutis cantori Larval
Lymnaea parva Larval
Lymnaea swinhoei Larval
Non-operculate snails Larval
Physella acuta Larval
Radix auricularia japonica Larval

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])
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)

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Eupteromalus Parasite Pupae
Hirsutella citriformis Pathogen
Phygadeuon yonedai Parasite Pupae
Trichogramma japonicum Parasite Eggs not specific N

Notes on Natural Enemies

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Sciomyzid larvae are attacked by a wide range of predators such as fish, Odonata, Hemiptera, Coleoptera, Planaria and Hydra (Neff and Berg, 1966). In California, USA, the adults are preyed on by generalist predators such as birds, frogs, toads, spiders, Odonata and robber flies (Asilidae) (Fisher and Orth, 1983). The most common natural enemies of sciomyzids are parasitoid Hymenoptera, particularly ichneumonids, which attack the egg, larval and pupal stages. Both bacteria and viruses are known to attack Sepedon larvae (Neff and Berg, 1966).

Rombach and Roberts (1989) recorded the fungal pathogen Hirsutella citriformis (Hypocreales) attacking S. aenescens (Knutson and Vala, 2011).

Nagatomi and Kushigemachi (1965) recorded Trichogramma japonicum as an egg parasite of S. aenescens in Japan: of 134 egg masses containing 2123 eggs collected, 117 masses (87.3%) and 1395 eggs (65.8%) were parasitized (Knutson and Vala, 2011). S. aenescens is thought to play a role in the biological control of rice stem borers (Lepidoptera) by serving as an alternative host to Trichogramma parasitoids when egg masses of the borers are not present (Beaver et al., 1997), but further data are required to confirm this.

Pteromalid parasites of an unknown species of Eupteromalus have been reared from puparia of S. aenescens in Thailand (Beaver et al., 1993, Knutson and Orth, 1984).

A new species of ichneumonid, Phygadeuon yonedai sp. nov., was recorded emerging from a puparium of S. aenescens collected in Japan in 1984 (Kusigemati, 1986).

Means of Movement and Dispersal

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Natural Dispersal

The adults of Sepedon are poor and slow fliers and tend to stay in the larval breeding sites, moving from one resting place to another nearby (Neff and Berg, 1966; Knutson and Vala, 2011).

Accidental Dispersal

Yano (1978) reports the collection of two specimens (one male and one female) of S. aenescens on a ship in the East China Sea, about 160 km from the coast of China during July 1969. The female was attracted to light.

Intentional Introduction

S. aenescens (as Sepedon sautei) was introduced to the Hawaiian Islands from Japan in 1966­-67 for the control of the lymnaeid snail, Fossaria viridis, an intermediate host of the liver fluke, Fasciola gigantica Cobbold, and became established there (Davis and Chong, 1968, 1969; Davis, 1974; Berg and Knutson, 1978; Knutson and Vala, 2011). It was also introduced into southern California in 1975 in order to control Fasciola gigantica, but it is not known to be established there (Knutson and Orth, 1984; Knutson and Vala, 2011) (for more information on introduction as a biological control see History of Introduction/Spread section).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Biological controlIntroduced to control lymnaeid snail vectors of liver fluke in Hawaii and California Yes Davis and Krauss, 1967; Knutson and Orth, 1984

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
AircraftEggs Yes Knutson and Orth, 1984

Impact Summary

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CategoryImpact
Environment (generally) Negative

Environmental Impact

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Impact on Biodiversity

As many species of sciomyzid are generalist feeders, their introduction as biological control agents in habitats where they are not native has caused concern that they may attack non-target indigenous species in addition to the intended prey, resulting in biodiversity loss (Barker et al., 2004). Together with habitat loss, predation of the eggs and adults of native Hawaiian lymnaeid snails by both S. aenescens and Sepedon macropus represents a significant threat to their survival. One species of particular concern is Newcomb’s snail (Erinna newcombi), a Threatened species according to the US Endangered Species Act, found only in ten small sites in six watersheds in the mountainous interior of the island of Kauai in Hawaii, USA (US Fish and Wildlife Service, 2004). This species is classified as Vulnerable B1ab(iii) in the IUCN Red List of Threatened Species (Smith and Seddon, 2003).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Erinna newcombi (Newcomb's snail)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesHawaiiSmith and Seddon, 2003

Risk and Impact Factors

Top of page Invasiveness
  • Has a broad native range
  • Tolerant of shade
Impact outcomes
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Likelihood of entry/control
  • Difficult to identify/detect in the field

Uses

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Economic Value

Eleven species of Sciomyzidae, including S. aenescens, have been introduced to Hawaii, USA, in attempts to find biological control agents of the snail vectors of the liver fluke, Fasciola gigantica (Davis, 1974; Barker et al., 2004). The liver fluke has been recorded in the Hawaiian Islands since 1892 and is the causative agent of fascioliasis, one of the most important parasitic diseases of beef and dairy cattle there (Davis, 1960).

Of the species of Sciomyzidae introduced to Hawaii for the biological control of liver fluke, only S. aenescens and Sepedomerus macropus became successfully established, with S. aenescens attaining greater populations than S. macropus (Berg and Knutson, 1978). They appeared to be successful in reducing the transmission rate of fascioliasis because the incidence of liver fluke in the livers of slaughtered cattle was found to have dropped in Oahu, Maui and Hawaii between 1966 and 1972 (Davis, 1974) and also on Kauai between 1972 and 1976 (Berg and Knutson, 1978). However, the success of these sciomyzids in controlling fascioliasis has not been assessed since the early 1970s (Barker et al., 2004).

S. aenescens is an effective predator of the non-native lymnaeid snail Fossaria viridis, an intermediate host of the liver fluke. F. viridis is abundant in swamps, streams, taro and watercress habitats on the Hawaiian islands (Davis et al., 1961), together with another non-native aquatic snail, Pseudosuccinea columella, probably introduced to Hawaii from continental USA. P. columella has been shown to be a vector of the liver fluke in the laboratory (Alicata, 1953).

The taxonomy of the lymnaeid snails on Hawaii is confusing. Early reports refer to another non-native lymnaeid snail, Lymnaea (Fossaria) ollula, as being an intermediate host of the liver fluke in Hawaii (Alicata and Swanson, 1937; Alicata, 1938; Chock et al., 1961; Davis et al., 1961), but it is believed these early records are a misidentification of Fossaria viridis (Morrison, 1968; Cowie, 1997). However, Cowie (1997) states that ollula may be a junior synonym of viridis, which has not been formally recognized. Other authors refer to Galba (= Lymnaea) viridis (Davis, 1972) or Galba viridis (Funasaki et al., 1988), as Galba is sometimes treated as a senior synonym of Fossaria (Cowie, 1997). Knutson and Vala (2011, p. 6) refer to these two species as Austropeplea ollula [Lymnaea ollula] and Austropeplea viridis.

Social Benefit

As well as being vectors of the liver fluke, lymnaeid snails are also an intermediate host of duck schistosomiasis, the cercaria of which cause paddyfield dermatitis in people (Fan et al., 1993). Therefore control of these snails using sciomyzids brings benefits to people and wildlife.

Detection and Inspection

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S. aenescens can be detected by sweep netting and use of Malaise traps (e.g. Cho et al., 2011).

Similarities to Other Species/Conditions

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Knutson and Orth (1984) list the various features used to distinguish the Sepedon group from other Sciomyzidae. Eight genera are recognized in the Sepedon group: Ethiolimnia, Teutoniomyia, Thecomyia, Sepedoninus, Sepedonella, Sepedon, Sepedomerus and Sepedonea (Marinoni and Mathis, 2006). The larvae of Sepedon and Sepedomerus are similar to those of Sepedonea. The most reliable character to separate these larvae is the dorsal-most accessory tooth of the cephalopharyngeal skeleton; in Sepedomerus and Sepedon the accessory teeth are generally subequal in size and evenly, usually lightly, sclerotized, while in Sepedonea the dorsal-most accessory tooth is larger and more darkly sclerotized (Friedberg et al., 1991).

Within the genus Sepedon, three sibling species belong to the Sepedon sphegea species complex: S. sphegea, S. aenescens and S. femorata. These species have a bluish-black body and yellowish-orange legs, but lack the blackish parafrontal spots that occur in other species of Sepedon. The species in the complex can be distinguished from each other by several features. The most obvious is the first antennal segment, which in S. aenescens varies from yellowish to pale brown but is lighter than the second segment, whereas in S. femorata and S. sphegea the first to third antennal segments are all dark brown to black. Other features that distinguish these species are: the degree of bristling on the front femur (absent in S. aenescens and S. sphegea and heavy in S. femorata); an anteroventral projection on the cercus in S. aenescens and S. femorata but not in S. sphegea; and the shape of the fifth sternum (Knutson and Orth, 1984).

Adults of Sepedon appear more slender and elongate than other Tetanocerinae. They are easily recognized in the field by their distinctive body form, posture and habits. They rest on leaves, facing down the vegetation, with the wings laid flat on their backs and their hind legs folded, the tip of the abdomen nearly touching the leaf and the head lifted high, in a characteristic frog-like pose (Neff and Berg, 1966).

The bluish-black colour of the head and body of S. aenescens can be used to distinguish it from Sepedon oriens, which has a yellow head and brown thorax (Sueyoshi, 2001).

References

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Principal Source

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Draft datasheet under review

Contributors

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25/05/2016 Original text by:

Angela Whittaker, Consultant, UK

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