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Datasheet

Erionota torus
(banana skipper)

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Datasheet

Erionota torus (banana skipper)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Erionota torus
  • Preferred Common Name
  • banana skipper
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • E. torus is primarily of concern as a pest of Musa spp. (banana, plantain). The larvae feed on the leaves and construct a large leaf roll in which they feed, thus causing more damage to the leaf that t...

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    Oxfordshire
    OX10 8DE
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Identity

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Preferred Scientific Name

  • Erionota torus Evans, 1941

Preferred Common Name

  • banana skipper

Local Common Names

  • India: Sikkim palm dart; Sikkim palm red-eye
  • Malaysia: Chinese banana skipper
  • Thailand: giant skipper

Summary of Invasiveness

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E. torus is primarily of concern as a pest of Musa spp. (banana, plantain). The larvae feed on the leaves and construct a large leaf roll in which they feed, thus causing more damage to the leaf that that of feeding alone. Its indigenous range is from northern India and Southern China to South East mainland Asia. It has spread to Mauritius, southern Philippines, Taiwan, Japan and western India. As an introduced pest it is extremely damaging to Musa spp. but has been brought under effective biological control by the introduction of parasitoids in Mauritius and perhaps Taiwan. Because it has been confused with E. thrax in the past, it has not received the attention it deserves as a potential invasive pest species.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Lepidoptera
  •                         Family: Hesperiidae
  •                             Genus: Erionota
  •                                 Species: Erionota torus

Notes on Taxonomy and Nomenclature

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This species was described by Evans (1941) and separated from the superficially very similar Erionota thrax (Linnaeus); both are known as the banana skipper. There have been no subsequent name changes. In the applied entomology literature, E. torus has frequently been confused with E. thrax where the two occur together in South-East Asia. The common name ‘rounded palm red-eye’ has been used quite widely, but as Cock (2015) shows there is no evidence that palms are food plants, all common names based on ‘palm’ should be discouraged.

Description

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Cock (2015) analysed the food plant records of E. torus, and concluded that the normal food plants are Musa spp. (Musaceae), although occasionally, perhaps under outbreak conditions, some other species of Zingiberales such as Strelitzia may be used.

The early stages cannot be distinguished from those of E. thrax, which feeds on the same food plants. Adults lay eggs singly or in small groups on the food plant. The newly eclosed larvae immediately make a leaf roll shelter, which may be extended right through to pupation, or one or more new shelters may be constricted during the larval development. The leaf roll shelter of a fully-grown caterpillar is large, conspicuous and distinctive. In making the shelter, considerably more leaf material is incorporated than is eaten, so that the defoliation of the host plant is disproportionate. The caterpillar is covered with white, waxy powder and has a dark head. The pupa which is formed in a pouch within the leaf roll shelter does not have any important distinguishing structures or markings. The adult butterfly is large for the family, and flies at dusk.

The following is largely based on Bascombe et al.’s (1999) and Cock’s (2015) accounts, except as indicated. The egg is 1.8-2.2 mm in diameter, dome-shaped with 22-24 fine ribs stopping short of the micropyle; they are pink or variegated pink and yellowish white when laid, becoming paler as they develop. They are usually laid on the Musa sp. leaf underside, and may be laid singly, but more often in clusters of up to 30, rarely 50. In contrast, Igarashi and Fukuda (2000) state that the ova are 2.2 mm in diameter, and normally laid singly on the leaf upper side, although batches of 3-36 are recorded; this may reflect a generalization from a relatively small number of observations.

On hatching the larva eats the egg shell, and then moves to the edge of the leaf to make its first shelter, which is either a simple fold parallel and close to the edge of the leaf, or a cone-shaped roll formed by making a curved cut from the edge of the leaf and rolling the resultant flap under. This first cut may be curved towards the leaf base or away from it, but all subsequent shelters are made with the cut curved towards the base of the leaf. Larvae feed on the inner parts of the roll, which is closed at the inner end (nearest midrib) and open at the distal end, where frass may accumulate. As the larva grows, it extends the cut and rolls more of the leaf into the shelter. Additional shelters are constructed if the shelter is damaged, unable to be rolled further or encounters another shelter.

Igarashi and Fukuda (2000) indicate that the leaf shelters of E. torus and E. thrax are rolled in opposite directions, although it is not clear from the text and diagrams whether this means clockwise and anti-clockwise when seen from above, or one with the leaf under surface on the inside of the shelter and the other with the leaf under surface on the outside of the shelter. In any case, they seem to be incorrect, as both species roll the leaf flap clockwise or anti-clockwise depending on which side of the leaf the shelter is formed, and the shelters almost always have the leaf underside inside the shelter for both species.  Igarashi and Fukuda (2000) also indicate that the top end of the larval leaf shelter is open and that the larva comes out of this opening to feed on the leaf by night; this also seems to be incorrect as photographs of the leaf shelters indicate no feeding outside the shelters (Hoffmann, 1935; Teruya et al., 1973; Teruya, 1997; Bascombe et al., 1999) and all the indications are that the larvae feed inside the tube. Working in Japan, Makibayashi (1981) provides a detailed description with clear diagrams to show how a final instar caterpillar makes a new leaf shelter. His diagrams show that the leaf roll is pulled into position by silk strands between the leaf roll and the adjacent unaffected part of the leaf, which in due course, is pulled into the shelter in turn.

From an early age, the larva is covered with an increasingly thick layer of white powder, so that the body appears white with erect, pale setae partially covered with the powder, and the uniformly dark head is partially obscured with the white powder. The larva grows to 55 mm in length (Igarashi and Fukuda, 2000) and is covered with white flocculence as it prepares for pupation.

Pupation takes place in a pocket made from the innermost roll of the final leaf roll shelter, lined with a thin layer of silk and closed at the distal end by a thin mesh, which is easily broken by the emerging adult. Ito and Nakamori (1986) refer to the pupal shelters in Japan as ‘trumpet shaped’, 1.5-2.0 cm diameter at the smaller [basal] opening, and 3.0-3.5 cm at the terminal opening; this does not seem to be typical.  Igarashi and Fukuda (2000) note that the pupal shelter is simpler than the larval shelter, having 3-4 layers rather than 5-6, and the pupa is formed with the head upwards, although the adult butterfly emerges from the bottom of the shelter.

The pupa is 45 mm long, pale brown with a variable and patchy covering of white powder. The proboscis extends almost to the cremaster. It is attached at the cremaster, and unlike many Hesperiinae the larva does not construct a silk girdle to hold the pupa in position.

The adult butterflies are large, brown and with yellowish hyaline markings on the forewings. The forewing length is about 32 mm in males and 35 mm in females.

Distribution

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Although no records from Cambodia have been found, E. torus is expected to occur in this country as it occurs in all the surrounding countries. Earlier records from Mauritius referred to this species as E. thrax due to an error of misidentification; E. thrax is not known to occur in Mauritius (Cock, 2015). Similarly, the species that has spread to the Pacific is E. thrax, but it has been incorrectly referred to as E. torus (Cock, 2015).

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

ChinaPresentPresent based on regional distribution.
-FujianPresentNative Not invasive Evans, 1941; Bascombe et al., 1999
-GuangdongWidespreadNative Invasive Hoffmann, 1935Recorded from ‘Kwangtung’ and ‘Canton’. Recorded in error as Erionota thrax as E. torus had yet to be described (see Cock 2015). Common on banana plants.
-GuangxiPresentNative Not invasive Evans, 1941; Bascombe et al., 1999Specimens in BMNH
-Hong KongWidespreadNative Not invasive Walker, 1895; Kershaw, 1907; Evans, 1941; Marsh, 1968; Bascombe et al., 1999
-MacauPresentNative Not invasive Easton and Pun, 1997; Cock, 2015Coloane Island
-YunnanPresentNative Not invasive Bascombe et al., 1999
-ZhejiangPresentNative Not invasive Bascombe et al., 1999
IndiaPresentPresent based on regional distribution.
-AssamPresentNative Not invasive Evans, 1941Specimens in BMNH.
-KeralaLocalisedIntroduced2014 Invasive Raju et al., 2014Western Ghats
-SikkimPresentNative Not invasive Evans, 1941Type locality; specimens in BMNH
-UttarakhandPresentNative Not invasive Mackinnon and Nicéville, 1898; Evans, 1941
JapanPresentPresent based on regional distribution.
-Ryukyu ArchipelagoLocalisedIntroduced1971 Invasive Teruya et al., 1973Okinawa (Jaaragru, Kishaba)
LaosPresentNative Not invasive Motono and Negishi, 1989; Osada et al., 1999Very rare.
MalaysiaPresentPresent based on regional distribution.
-Peninsular MalaysiaLocalisedNative Not invasive Evans, 1941Malacca, Perak. Specimens in BMNH.
MyanmarLocalisedNative Not invasive Evans, 1941Dawei (as Tavoy). Specimen in BMNH.
NepalPresentNative Not invasive Smith, 1994; Smith, 2006
PhilippinesLocalisedNative Not invasive Jong and Treadaway, 1993; Jong and Treadaway, 1993; Hardy and Lawrence, 2017Cebu, Dinagat, Leyte, Mindanao, Negros, Panay and Samar
Sri LankaPresentIntroduced2015Gunawardana et al., 2015
TaiwanPresentIntroduced1986 Invasive Chiang and Hwang, 1991; Chu, 1998
ThailandLocalisedNative Not invasive Pinratana, 1985Bangkok, Ratchaburi, Trang, Yala.
VietnamPresentNative Not invasive Evans, 1941; Monastyrskii and Devyatkin, 2001; Monastyrskii and Devyatkin, 2003Recorded throughout Vietnam.

Africa

MauritiusWidespreadIntroduced1968 Invasive Cock, 2015Black River. Earlier records of E. thrax are based on a misidentification of E. torus.

History of Introduction and Spread

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E. torus spread to Mauritius around 1968 (reported as E. thrax, but see Cock (2015)), southern Japan in 1971 (Teruya et al., 1973), Taiwan in 1986 (Chu, 1988; Chiang and Hwang, 1991), the southern Philippines probably in the early 1980s (Cebu, Dinagat, Leyte, Mindanao, Negros, Samar; De Jong and Treadaway (1993)), and has just been found in the Western Ghats of India (Raju et al., 2014). There is a single male specimen labelled Sarawak in the Natural History Museum, London, but the absence of any other records from Borneo suggests its presence there should be considered unconfirmed (Cock, 2015). It does not seem to be present in Sumatra, Java or the rest of Indonesia.

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Japan China 1971 Yes No Cock (2015); Teruya (1997) Assumption re. accidental introduction
Kerala 2014 Yes No Cock (2015); Raju et al. (2014) Assumption re. accidental introduction
Mauritius Peninsular Malaysia c 1968 Military movements (pathway cause) Yes No Cock (2015); Waterhouse and Norris (1989) Assumption re. accidental introduction
Philippines Early 1980s Yes No Cock (2015); Jong and Treadaway (1993) Assumption re. accidental introduction
Taiwan China 1986 Yes No Chiang and Hwang (1991); Chu (1998); Cock (2015) Assumption re. accidental introduction

Risk of Introduction

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Since the adults fly at dusk and may be attracted to lights, they could well settle in vehicles such as trucks, boats and planes that may be loaded under lights in the evening, and hence transported long distances. Eggs, larvae and pupa on growing plants or plant material may be transported, but the leaf rolls of larger larvae and pupae are so conspicuous that accidental movement of these stages seems less likely.

The major translocations of E. torus were most probably mediated by aircraft flights carrying infested plants or planting materials, infested leaves or adult butterflies. Military flights have been suggested as the route for the spread to Mauritius: E. torus is ‘thought to have been introduced in military aircraft based in Malaysia in 1968’ (Waterhouse and Norris, 1989).

The fact that E. torus has not spread more widely already, e.g. within the parts of Indonesia where it does not occur naturally, suggests that long distance flights over sea do not occur. Inter-island movement of boats seems a more likely pathway of introduction (Cock, 2015).

In view of the confusion between E. torus and E. thrax that has arisen, it is worth recognizing the possibility that in the last 65 years or so since Evans (1949) completed his review of the Hesperiidae of the region, E. torus could have spread to areas where only E. thrax thrax was known (or vica versa), and easily been overlooked (Cock, 2015). This possibility merits checking with recent material, for example in the island of Borneo where there is already a single record of E. torus, and Sumatra and Java which are in relatively easy reach of peninsular Malaysia.

Habitat

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E. torus seems to occur wherever wild and cultivated Musa spp. food plants occur. It is not known whether E. torus and E. thrax show different habitat preferences, but this is a possibility.

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Principal habitat Harmful (pest or invasive)
Managed forests, plantations and orchards Principal habitat Harmful (pest or invasive)
Rail / roadsides Principal habitat Harmful (pest or invasive)
Rail / roadsides Principal habitat Natural
Urban / peri-urban areas Principal habitat Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Natural forests Principal habitat Natural

Hosts/Species Affected

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Because of the confusion between E. thrax and E. torus in the literature, the recorded food plants of E. torus can only be considered reliable where there are voucher specimens, or they are from areas where E. thrax does not occur. Thus bananas and plantains are known food plants, and Manila hemp (M. textilis) and wild bananas (M. sapientum) are likely to be food plants.

Records from palms exist, e.g. Robinson et al. (2001) list Caryota sp(p). and Roystonea regia. In their treatment of pests of rattan palm in Peninsular Malaysia, Maziah et al. (1992) include E. torus, although Steiner (2001) and Steiner and Aminuddin (2001) subsequently indicate that this record should be treated as E. acroleucus (= E. hiraca). The leaf-roll shelters of E. torus can only be made using a leaf with a large flat lamina, e.g. Musa spp., Heliconia spp., some Strelitziaceae, Marantaceae, Zingiberaceae, etc. (all in the Zingiberales), and unlikely to be possible on pinnate palms.

In a laboratory study in Taiwan, Tsai et al. (1990) fed cohorts of each of the five instars of larvae of E. torus with cut portions of leaves of banana, Strelitzia reginae (bird of paradise flower), Cocos nucifera (coconut), areca nut (Areca catechu), Bambusa oldhamii (bamboo) and sugarcane (Saccharum officinarum). Feeding was most extensive on banana, but almost as heavy on S. reginae; there was very little feeding on coconut (none for the cohort of instar 1), less on areca nut and none on bamboo or sugarcane. Average survival for all instar cohorts was 50% on S. reginae, 5% on coconut and 0% on bamboo and sugarcane. This is a measure of the survival of larvae transferred to a plant other than banana, and does not reflect what would happen following oviposition on that plant in the field. If there was no feeding in instar 1 on coconut, all larvae would die in the field, while the data does not allow us to interpret what total mortality would be on S. reginae, it would be more than 50%. In this experiment, the larvae on banana are reported to have all completed development, but in a parallel experiment, only 34 and 21% of individuals completed their metamorphosis on banana at 20 and 30°C, respectively, most mortality occurring in instars 1 and 2. It is difficult to know how to interpret these two apparently conflicting results. However, we can conclude that sugarcane, bamboo, areca nut and coconut are unsuitable food plants, while S. reginae is less suitable than banana (Cock, 2015).

There are internet records of E. torus using Canna sp(p). as food plants (e.g. Taiwan, 2014), but these have not been traced to any formal publication, and may well be derived from the records for E. thrax, when the name E. torus was misapplied to that species.

Cock (2015) concluded that all food plant records of E. torus from palms should be disregarded, and although the possibility of other Zingiberales being used as food plants cannot be discounted, none should be considered confirmed at this time.

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Musa x paradisiaca (plantain)MusaceaeMain

Growth Stages

Top of page Flowering stage, Fruiting stage, Vegetative growing stage

Symptoms

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The leaf rolls made by E. torus are large, obvious and easily located and recognized. However, they cannot be distinguished from those of E. thrax.

List of Symptoms/Signs

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SignLife StagesType
Leaves / external feeding
Leaves / leaves rolled or folded
Whole plant / external feeding

Biology and Ecology

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Reproductive biology

In moist tropical areas E. torus probably breeds continuously. Further north, adult activity is restricted to the warmer months.

Physiology and phenology

In Hong Kong, Bascombe et al. (1999) indicate that adults are first seen in April and are reasonably common from July to October. Hoffmann (1935) reports at least two generations, maybe three in Guangdong.

Longevity

In Hong Kong, Bascombe et al. (1999) give the egg stage as 7 or more days, the larva 21-24 days and the pupa 11-15 days. Adult longevity does not seem to have been documented.

Activity patterns

In the northern part of its range, E. torus overwinters as a larva (Bascombe et al., 1999).

Population size and density

Very little reliable information. When newly introduced in Mauritius, E. torus was very common, causing substantial damage (Monty 1970), but has been scarce since the introduction of biological control agents (Monty, 1977; Waterhouse and Norris, 1989). A similar pattern occurred in Taiwan, although the role of the introduced biological control agents has not been established (Teruya, 1997; Lo, 2002).

Nutrition

The larvae feed only on the leaves of their food plants. Adults have a long proboscis and feed on nectar, although the preferred nectar sources have not been documented.

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])
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)
35 -20

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Agiommatus Parasite Eggs
Agiommatus sp. nr. sumatraensis Parasite Eggs Mauritius Banana
Anastatus sp. near pearsali Parasite Larvae
Chalcidoidea Parasite Eggs
Cotesia erionotae Parasite Larvae Mauritius, Taiwan Banana
Elasmus philippinensis Parasite Larvae
Exorista japonica Parasite Pupae
Leurocerus hongkongensis Parasite Eggs
Ooencyrtus pallidipes Parasite Eggs Mauritius, Taiwan Banana
Scenocharops Parasite Larvae Mauritius Banana
Tachinidae Parasite Pupae
Trichogrammatidae Parasite Eggs
Xanthopimpla Parasite Pupae
Xanthopimpla regina Parasite Pupae

Notes on Natural Enemies

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Cock (2015) summarizes the available records of natural enemies of E. torus, based on those reported from areas where only E. torus occurs. In areas where E. torus and E. thrax occur together, the published records refer to E. thrax, but may have been derived from either or both Erionota spp. It seems likely that most or all of the parasitoids of E. thrax will also attack E. torus, but detailed information on all these species usually has been associated with E. thrax and not E. torus in the literature.

Cotesia erionotae (Braconidae) and Ooencyrtus pallidipes (Encyrtidae) have been effective as biological control agents for E. torus in Mauritius and Taiwan, and for E. thrax in Guam, Saipan, Hawaii and Papua New Guinea.

Means of Movement and Dispersal

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Natural dispersal

Adults fly, but there is no information on the distance and duration of their flights.  Given their size, it might be anticipated that they are able to fly long distances, but this is speculative.

Vector transmission (biotic)

None.

Accidental introduction

Since the adults fly at dusk and may be attracted to lights, they could well settle in vehicles such as trucks, boats and planes that may be loaded under lights in the evening, and hence may be transported long distances. Eggs, larvae and pupa on growing plants or plant material may be transported, but the leaf rolls of larger larvae and pupae are so conspicuous this seems less likely.

The major translocations of E. torus were most probably mediated by aircraft flights carrying infested plants or planting materials, infested leaves or adult butterflies. Military flights have been implicated or suggested as the route for the spread to Mauritius: E. torus is ‘thought to have been introduced in military aircraft based in Malaysia in 1968’ (Waterhouse and Norris, 1989). Inter-island movement of boats between nearby islands seems a likely pathway of introduction (Cock, 2015).

The fact that E. torus has not spread more widely already, e.g. within the parts of Indonesia where it does not occur naturally, suggests that long distance flights over sea do not occur (Cock, 2015).

Intentional introduction

None.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Crop productionMovement of banana planting material with early stages Yes Cock, 2015
HitchhikerMotor vehicles, boats and aircraft could all carry hitchhiker adults of E. torus. Yes Yes Cock, 2015
Military movementsMilitary aircraft have been suggested as the pathway for entry to Mauritius. Yes Cock, 2015; Waterhouse and Norris, 1989
Nursery tradeLocal movement of planting material will facilitate the movement of associated early stages. Yes Cock, 2015

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
AircraftAdults attracted to lights when aircraft are loaded at night are likely to be rare hitchhikers Yes Cock, 2015
Bulk freight or cargoAdults attracted to lights when motor vehicles and boats are loaded at night are likely to be rare h Yes Yes Cock, 2015
Plants or parts of plantsLocal movement of planting material may facilitate movement of associated early stages of E. torus. Yes Cock, 2015

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Leaves eggs; larvae; pupae Yes Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Roots
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches
True seeds (inc. grain)
Wood

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact Summary

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CategoryImpact
Cultural/amenity Negative
Economic/livelihood Negative

Economic Impact

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In its indigenous range, E. torus is a minor pest of bananas, which occasionally may develop short-term outbreaks. In much of this range this damage is treated in the economic literature as being caused by E. thrax, whereas it could be due to either or both species.

Once established in Mauritius, E. torus soon became a serious pest on tall banana varieties in urban areas, but not in rural commercial plantations of dwarf Cavendish type bananas (Monty, 1970; Waterhouse and Norris, 1989). Since the biological control programme in the 1970s, it has not been a problem.

Social Impact

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As an introduced species, before biological control is implemented, E. torus would be a pest of bananas grown in gardens and ornamental Musa varieties.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Is a habitat generalist
  • Highly mobile locally
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
  • Negatively impacts livelihoods
Impact mechanisms
  • Herbivory/grazing/browsing

Diagnosis

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Adults should be distinguished from those of E. thrax by examination of the external genitalia using a binocular microscope when practical, or by dissection and examination of the genitalia under a binocular microscope when external inspection is not possible.

Detection and Inspection

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The eggs and leaf rolls in which larvae and pupae rest can be detected by visual inspection of leaves of banana plants.

Techniques to detect adults in motor vehicles, boats and aircraft have not been formalized, but the adults are large and should be easily detected in any careful and comprehensive visual inspection.

Similarities to Other Species/Conditions

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The adults of E. torus and E. thrax are similar in colour and markings. The shape of the forewing can usually be used to separate the males of the two species if they are compared side by side: in E. torus the male forewing outer margin is relatively rounded, whereas that of E. thrax is straighter and the apex more pointed. However, if only one species is present, this difference is unlikely to be clear to the inexperienced observer. Adults are best identified by examination of the male or female genitalia (Evans, 1941, 1949), which are well illustrated for both species by Inoué and Kawazoé (1970).

The larvae of E. torus and E. thrax both feed on Musa spp. At this time there is no way to distinguish between the eggs, larvae, leaf rolls, or pupae of the two species based on their appearance, so that where both species occur together (north-east India to peninsular Malaysia and southern Philippines) all observations need to be supported by reared identified adult specimens. It should be possible to use DNA barcoding to separate the early stages but this has not been attempted as yet (Cock, 2015). There are no similar species that feed on banana.

The early stages of other Erionota spp. are similar but they do not feed on Musa spp. and those that are known feed on palms. The commonest and most widespread of these is E. acroleucus (Wood-Mason and De Nicéville), which is found as subspecies apex Semper from North-East India through South-East Asia, to Java, Borneo and the Philippines, and as additional subspecies on the Andaman Islands and Sulawesi (Evans, 1949; Vane-Wright and De Jong, 2003). Cock (2015) concludes that the larvae of this species feed exclusively on palms. The adults usually have a white apex to the forewing upper surface and are smaller than E. torus, but when the white marking is missing, confirmation by examination of the male or female genitalia will be necessary (Evans, 1941, 1949); these are also illustrated by Inoué and Kawazoé (1970).

Prevention and Control

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Prevention

SPS measures (quarantine, certification, prohibition)

Musa planting material should only be moved locally and not across international borders, or between islands.

Early warning systems

There are no specific systems needed as farmers and the public will very quickly spot the large leaf rolls made by the larvae.

Rapid response

There are no specific responses in place.

Public awareness

Because there are no specific high risk areas identified, public awareness is not a priority beyond that which should be encouraged regarding alien species as a whole.

Eradication

Eradication has not been attempted.

Containment/zoning

Containment has not been attempted.

Control

Physical/mechanical control

Hand-picking in a garden / back-yard situation is probably practical.

Biological control

E. torus was first reported in Mauritius in 1970 as E. thrax (Monty, 1970). Once established in Mauritius, it soon became a serious pest on tall banana varieties in urban areas, but not in rural commercial plantations of dwarf Cavendish type bananas (Monty, 1970; Waterhouse and Norris, 1989). R.A. Syed of the Commonwealth Institute of Biological Control (part of CABI) studied the parasitoids of E. thrax in Sabah (Syed, 1970) and sent shipments of larval parasitoids Scenocharops sp. and Cotesia erionotae, and egg parasitoids Ooencyrtus pallidipes and Agiommatus sp. nr. sumatraensis to Mauritius in 1971-1973. All four species were released in Mauritius. C. erionotae and O. pallidipes became established, and although there were recoveries of Agiommatus sp. it did not persist. The parasitoids quickly provided effective biological control. In 1975 a cyclone severely damaged banana plants and drastically reduced banana skipper and parasitoid populations which, nevertheless, built up again in 1976. None of the parasites established earlier was recovered in the 2 years following the cyclone, but damage to banana by the skipper was recorded as being very low in 1978 and it remained uncommon. Davis and Barnes (1991) report that specimens of E. torus (as E. thrax) were taken on the west coast of Mauritius in 1979, but it was not seen elsewhere between the years 1976 and 1980, so that its status was considered unclear. Williams (1989) considered it (as E. thrax) ‘uncommon for reasons that are not clear’. Collectors from the African Butterfly Research Institute found early stages in 2014 (T.C.E. Congdon, pers. comm., 2014), so E. torus continues as an uncommon species of no significant pest status in Mauritius, almost certainly kept under effective biological control by its introduced parasitoids. None of the other species of Hesperiidae found on Mauritius are known to be parasitized by any of the parasitoid species introduced against E. torus (J. Monty, pers. comm., 1987 in Waterhouse and Norris (1989)).

Based on the programme already carried out for Mauritius (purportedly on E. thrax but actually on E. torus) when E. thrax appeared in Hawaii, a biological control programme was immediately started (Waterhouse and Norris, 1989). In 1973, O. pallidipes was introduced from Guam where it seemed to be an accidental introduction itself, and in 1974 C. erionotae was introduced and released, initially from Thailand (early 1974) and then from Sabah (late 1974). Both parasitoids were sent from Hawaii to Taiwan for the control of E. torus; they were released in 1987 and both became established (Lo, 2002). The impact has not been fully reported, although Teruya (1997) found E. torus to have ‘a low pest status’, infestation ranging from 0.1 to 7% with an average of 4%, but he did not find the introduced parasitoids.

Chemical control

No products have been identified as registered for use against this pest.

Host resistance (incl. vaccination)

Anecdotal observations suggest there may be significant differences in the frequency of outbreaks on different varieties in the native range (Cock, 2015), but this has not been systematically evaluated for E. torus.

IPM

In its indigenous range, localized outbreaks of E. torus are expected to die out quickly due to the action of natural enemies, particularly parasitoids. The use of pesticides in banana plantations should be done in such a way as to minimize the impact on natural enemies, but guidelines specific to the natural enemies of E. torus have not been established. In its introduced range, the introduction of biological control agents has solved the problem, and should new introductions occur this should be the preferred method of control.

Monitoring and surveillance (incl. remote sensing) 

No monitoring systems have been proposed for E. torus, although scouting for leaf rolls, which are visible from 20 m (Cock, 2015), would make this easy to set up.

Mitigation

Once biological control is functioning, this is not been necessary.

Gaps in Knowledge/Research Needs

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Cock (2015) identified the following research gaps in relation to E. torus:

  • Molecular methods, particularly barcoding, are needed to confirm identifications of early stages and develop identification tools.
  • Further collections and reliable identification of adults (by examination of the genitalia and/or barcoding) are needed to confirm that E. torus feeds only on Musa spp. (and maybe a few similar species).
  • As yet, there is no reliable way to separate the early stages of E. thrax, E. torus and E. acroleucus morphologically. Careful study and documentation of reared material, supported by reared vouchers and barcoding of individuals, is needed to see if diagnostic criteria can be found.
  • Careful observation and behavioural studies of how the larvae construct their shelters on different food plants may provide additional diagnostic characters.
  • Once the larvae of E. thrax and E. torus can be distinguished, the host-parasitoid relations for the genus can be clarified; do parasitoids accept both equally or is there specialization for one or the other?
  • Recognizing the possibility that E. torus may have spread into areas where only E. thrax thrax was known, it would be worth making fresh collections to assess the situation, particularly in Borneo, Sumatra and Java.
  • E. torus is present in Mauritius at low densities, and seems to cause no economic damage.  It seems most likely that this is due to the continuing action of the introduced parasitoids, but this should be investigated.

The new report of E. torus devastating bananas in the Western Ghats of India suggests that biological control should be considered in this situation. However, a careful risk analysis with regard to indigenous species of Hesperiinae would be needed first. To support this, a phylogenetic classification of the Hesperiinae would be necessary, to identify the most closely related genera which would be most at risk.

References

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Contributors

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11/12/14 Original text by:

Matthew Cock, CABI, Egham, UK.

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