- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Plant Trade
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Bactrocera tau Walker
Other Scientific Names
- Bactrocera (Zeugodacus) tau (Walker)
- Bactrocera hageni Hendel
- Bactrocera nubilus
- Chaetodacus tau (Walker)
- Dacus caudatus v. nubilus Hendel, 1912
- Dacus caudatus var. nubilus Hendel
- Dacus hageni de Meijere
- Dacus nubilus Hendel
- Dacus nubilus ssp. femoralis Hendel, 1933
- Dacus tau (Walker)
- Dasyneura tau Walker
- Zeugodacus nubilus (Hendel)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Diptera
- Family: Tephritidae
- Genus: Bactrocera
- Species: Bactrocera tau
Notes on Taxonomy and NomenclatureTop of page B. tau was first described by Walker in 1849. Much confusion has surrounded the naming of this species with many records published under the names Dacus hageni or D. nubilus. There are also some alternative generic combinations, most notably D. tau. It is a member of subgenus Zeugodacus and is therefore sometimes cited as Bactrocera (Zeugodacus) tau.
Some names listed as synonyms in taxonomic publications (e.g. Hardy, 1973) are not given above as research by White and Hancock (1997) has shown that these names belong to distinct species. These authors also recognised an undescribed (and very common) species from southern India, which has now been described as B. zahadi Mahmood in a partial revision of the group (Mahmood, 1999) . However, the true B. tau does appear to be the most widespread species in this complex and most data assigned to B. tau almost certainly do refer to this species. An exception is that some records of 'D. nubilus' refer to a species with a trilobed aculeus (Hardy, 1973) although the real D. nubilus has a pointed aculeus (White and Wang, 1992); these records actually belong to B. bezziana (Hering) and possibly another species.
DescriptionTop of page Adult description derived from computer generated description from White and Hancock (1997). Larval description from White and Elson-Harris (1994).
Head: Pedicel+1st flagellomere not longer than ptilinal suture. Face with a large dark spot in each antennal furrow. Frons - 2-3 pairs frontal setae, 1 pair orbital setae.
Thorax: Predominant colour of scutum fuscous. Postpronotal (=humeral) lobe entirely pale (yellow or orange). Notopleuron yellow. Scutum with lateral postsutural vittae (yellow/orange stripes), which are not tapered and which extend beyond the intra-alar setae. With a medial vitta. Scutellum not partly dark marked. Anepisternal stripe as narrow as notopleural spot. Yellow marking on both anatergite and katatergite. Postpronotal lobe (=humerus) without a seta. Notopleuron with anterior seta. Scutum with anterior supra-alar setae; with prescutellar acrostichal setae. Scutellum with basal as well as apical setae.
Wing: Length 6.1-8.8 mm. Wing with a complete costal band, which may extend below R2+3, but not to R4+5; expanded into a spot at apex which reaches about half way to M. Wing with an anal streak. Cells bc and c not coloured. No transverse markings. Cell bc and c without extensive covering of microtrichia. Cell br (narrowed part) with extensive covering of microtrichia.
Legs: Fore femur yellow / pale, sometimes with a dark preapical spot. Mid and hind femora pale.
Abdomen: Predominant colour orange-brown. Tergites not fused. Abdomen not wasp aisted. Pattern distinct. Tergite 3 with a transverse band. Tergite 4 either with antero-lateral recatngular marks or dark laterally. Medial longitudinal stripe on T3-5. Sternites dark, not yellow.
Terminalia and secondary sexual characters: Male wing without a bulla. Male tergite 3 with a pecten (setal comb) on each side. Male sternite 5 not V-shaped. Surstylus (male) with a long posterior lobe. Wing (male) with a deep indent in posterior margin. Hind tibia (male) with a preapical pad. Aculeus apex pointed.
The egg of B. olae (Gmelin) was described in detail by Margaritis (1985) and that of other species are probably very similar. Size, 0.8 mm long, 0.2 mm wide, with the micropyle protruding slightly at the anterior end. The chorion is reticulate (requires scanning elctron microscope examination). White to yellow-white in colour.
Third instar larva: Larva medium-sized, length 7.5-9.0 mm, width 1.0-1.5 mm.
Head: Stomal sensory organ rounded, with small sensilla; surrounded by 6-9 preoral lobes, those closest to mouth opening appearing similar to small oral ridges; oral ridges with 17-23 long rows of moderately long, bluntly rounded teeth; accessory plates forming numerous, serrated, long and short interlocking rows; mouthhooks large, heavily sclerotised, each with a strong apical tooth.
Thoracic and abdominal segments: Anterior margin of each thoracic segment with an encircling, broad band of spinules forming discontinuous rows. T1 spinules stout, sharply pointed and arranged dorsally and ventrally in small groups or plates, becoming discontinuous rows ventrally; T2 with short stout spinules, arranged in 6-9 discontinuous rows; T3 spinules similar to T2, arranged in 5-7 rows. A1-A8 without spinules dorsally, but with spinules forming creeping welts ventrally. Each creeping welt with small stout spinules arranged in 9-13 rows, with 2-5 rows anteriorly directed, the remainder posteriorly directed. A8 with intermediate areas large and protuberant (in mature larvae, almost linked by a long slightly curved pigmented transverse line), with obvious sensilla; dorsal and lateral areas also large and well defined. Anterior spiracles: 14-16 tubules. Posterior spiracles: Spiracular slits large, about 3.0-3.5 times as long as broad, arranged in a slightly radiating pattern and bordered by a strongly sclerotised rima. Spiracular hairs long, almost as long as spiracular slits, each with a broad trunk and branched in apical third to a half; hairs arranged in 4 large bundles of 14-18 in dorsal and ventral bundles, and 5-9 in each lateral bundle.
Anal area: Lobes large, protuberant, surrounded by 3-6 discontinuous rows of small, sharply pointed spinules. Spinules closest to anal lobes stout, long, curved and sharply pointed.
Barrel-shaped with most larval features unrecognisable, the exception being the anterior and posterior spiracles which are little changed by pupariation. White to yellow-brown in colour. Usually about 60-80% length of larva.
DistributionTop of page The map also includes records from the Natural History Museum, London, UK and the National Museum of Wales, Cardiff, UK. Records from India (except the north) and Sri Lanka all appear to have been based on misidentification of B. zahadi; many records from the Philippines refer to B. tapervitta Mahmood; most, perhaps all, records from Java were similarly based on misidentification and are referable to B. javadica Mahmood. Unfortunately the work of Mahmood (1999) was based on a study of limited material without reference to the wealth of recent survey collections accumulated by Australian and other projects, and has left the situation very confused. Baimai et al. (2000) presented evidence that even amongst populations in Thailand there may be more than a single species.
Distribution TableTop of page
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/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Bangladesh||Present||Akhtaruzzaman et al., 1999|
|Bhutan||Present||NHM London UK|
|Brunei Darussalam||Present||NHM London UK|
|China||Present||Present based on regional distribution.|
|-Chongqing||Present||Wang et al., 2007|
|-Fujian||Present||Wang, 19998; Liang et al., 1993|
|-Guangdong||Present||Wang, 1998; Liang et al., 1993|
|-Guangxi||Present||Wang, 1998; Liang et al., 1993|
|-Hainan||Present||Wang, 1998; Liang et al., 1993|
|-Hong Kong||Present||NHM London UK|
|-Hubei||Present||Wang, 1998; Liang et al., 1993|
|-Shaanxi||Present||Zhang et al., 2004|
|-Sichuan||Present||Wang, 1998; Liang et al., 1993|
|-Yunnan||Present||Wang, 1998; Liang et al., 1993|
|India||Present||Present based on regional distribution.|
|-Himachal Pradesh||Present||Pankaj and Sood Amit Nath, 2002|
|-Kerala||Widespread||David et al., 2008; David et al., 2008|
|-Uttar Pradesh||Present||Mahmood, 1999|
|-West Bengal||Present||Pal and Choudhuri, 2007|
|Indonesia||Present||Present based on regional distribution.|
|-Sumatra||Present||Mahmood, 1999; Hasyim et al., 2007|
|Malaysia||Present||White and Elson-Harris, 1994|
|-Peninsular Malaysia||Present||NHM London UK|
|-Sabah||Present||National Museum of Wales coll|
|-Sarawak||Present||NHM London UK|
|Myanmar||Present||NHM London UK|
|Singapore||Present||NHM London UK|
|Taiwan||Present||NHM London UK; Wang, 1998|
|Thailand||Present||NHM London UK|
|Vietnam||Present||Hardy, 1973; Mahmood, 1999|
Risk of IntroductionTop of page The major risk is from the import of fruit containing larvae, either as part of cargo, or through the smuggling of fruit in airline passenger baggage or mail. For example, in New Zealand Baker and Cowley (1991) recorded 7-33 interceptions of fruit flies per year in cargo and 10-28 per year in passenger baggage. Individuals who successfully smuggle fruit are likely to discard it when they discover that it is rotten.
Hosts/Species AffectedTop of page B. tau appears to show a preference for attacking the fruits of Cucurbitaceae, but it has also been reared from the fruits of several other plant families. Because of the recent separation of previously confused species the hosts data given here were all taken from a recently published host catalogue that was largely based on a 1990s survey carried out in Thailand and Malaysia (Allwood et al., 1999).
In addition to the hosts listed, other host species belonging to the family Cucurbitaceae are Coccinia grandis and Momordica cochinchinensis. There is also a confirmed record on Strychnos nux-vomica.
Growth StagesTop of page Fruiting stage
SymptomsTop of page Following oviposition there may be some necrosis around puncture mark ("sting"). This is followed by decompostion of the fruit.
List of Symptoms/SignsTop of page
|Fruit / internal feeding|
|Fruit / lesions: black or brown|
|Fruit / premature drop|
Biology and EcologyTop of page
The following is the typical life-cycle of a Bactrocera sp. Eggs are laid below the skin of the host fruit. These hatch within a day or 2 days and the larvae feed for another week or more. Pupariation is in the soil under the host plant for a week or more but may be delayed for several weeks under cool conditions. Adults occur throughout the year and begin mating after about 2 weeks; data from Christenson and Foote (1960). Adult flight and the transport of infected fruit are the major means of movement and dispersal to previously uninfected areas. Males are attracted to cue lure.
Some specific details are available for B. tau which suggest variation in parameters between hosts (Borah and Dutta, 1996), for example, 10 larvae in Momodica charantia to 40 in Lagenaria siceraria. In Trichosanthes cucumerina development was completed 11 days (up to 16 days in other hosts). Further details were given by Kabir et al. (1997), who noted that mating took place throughout the night and that adult longevity was up to 121 days for males and 191 for females; in Bangladesh populations peaked in September and to a lesser extend April.
[Erratum: In previous versions of this datasheet, it was stated that “many Bactrocera spp. can fly 50-100 km (Fletcher, 1989)” but a review of Fletcher (1989a) and Fletcher (1989b) by Hicks (2016, unpublished data, USDA) found no evidence to support this statement and it has been removed. Fletcher (1989b) provides dispersal data for only 11 of 651 species of Bactrocera, many of the case studies lack the necessary numerical data, and the study did not discern between active flight and passive wind-assisted dispersal. There are differences among fruit fly species and further studies are required to determine dispersal distances for individual species. For further information on trapping Bactrocera species to monitor movement, see Weldon et al. (2014).]
Natural enemiesTop of page
Notes on Natural EnemiesTop of page Bactrocera spp. can be attacked as larvae by either parasitoids or by vertebrates eating fruit (either on the tree or as fallen fruit). Mortality due to vertebrate fruit consumption can be very high as can puparial mortality in the soil, either due to predation or environmental mortality (see White and Elson-Harris, 1994, for brief review). Parasitoids appear to have little effect on the populations of most fruit flies and Fletcher (1987) noted that 0-30% levels of parasitism are typical. To date complete biological control, in the classical sense, has never been achieved for any Bactrocera or Dacus spp. (Wharton, 1989). Nonetheless, biological control programmes can result in significant reduction in pest populations. Such reductions have led to relatively pest-free cultivation of at least some less susceptible varieties of fruits and vegetables. Due to difficulties in verifying the identifications of both parasitoids and (in some cases) the fruit fly hosts, no attempt has been made to catalogue all natural enemy records; see White and Elson-Harris (1994) for major sources. Consequently, no comprehensive parasitoid list is given here. The natural enemies listed under synonyms "Dacus nubilus" and "D. hageni" are extracted from Wharton and Gilstrap (1983) and Waterhouse (1993):
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Fruits (inc. pods)||eggs; larvae||Yes||Pest or symptoms usually visible to the naked eye|
|Growing medium accompanying plants||pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Stems (above ground)/Shoots/Trunks/Branches|
|True seeds (inc. grain)|
ImpactTop of page Data on economic impact of B. tau is uncertain. Batra (1968) discussed the bionomics of a species called "D. hageni (=D. caudatus)" which may either refer to B. tau or to B. caudata (Wiedemann).
Detection and InspectionTop of page Fruits (locally grown or samples of fruit imports) should be inspected for puncture marks and any associated necrosis. Suspect fruits should be cut open and checked for larvae. Larval identification is difficult, so if time allows, mature larvae should be transferred to saw dust (or similar dry medium) to allow pupariation. Upon emrgence, adult flies must be fed with sugar and water for several days to allow hardening and full colour to develop, before they can be identified. Detection is described under Early Warning Systems.
Similarities to Other Species/ConditionsTop of page B. tau can easily be separated from most other pest species by having the costal band expanded into a spot at the wing apex; wing lacking any transverse markings; scutum (dorsum of thorax) having three longitudinal yellow stripes (vittae); face with a dark spot in each antennal furrow; and the scutellum with four setae (a basal as well as apical pair). In addition B. tau always has prescutellar acrostichal setae and this feature should normally separate it from B. depressa (Shiraki), which typically lacks these setae. However, aberrant specimens of this species (found in Japan and Taiwan) do occur which lack these setae; B. depressa is larger (wing length 8.9-9.2 mm) and has bands (or almost complete bands) across tergites 3, 4 and 5; B. tau only has a band across tergite 3, although the lateral markings of tergites 4 and 5 can be extended towards the midline. The most reliable character is in the aculeus structure; pointed in B. tau and trilobed in B. depressa. Larger than a house fly (wing length 6.1-8.8 mm).
Minimum characters to differentiate from all other Bactrocera and Dacus spp. (White and Hancock, 1997): Face with a dark spot in each antennal furrow. Lateral vittae extending anterior to suture and posteriorly to beyond intra-alar setae. Anepisternal stripe as narrow as the coloured part of the notopleural callus. Scutellum yellow, with basal as well as apical setae. No transverse markings on wings. Mid femur entirely pale. Transverse band across tergite 3. Tergite 4 with dark laterally or with antero-lateral dark marks. Sternites dark, not yellow. Aculeus pointed.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Many countries, such as the mainland USA, forbid the import of susceptible fruit without strict post-harvest treatment having been applied by the exporter. This may involve fumigation, heat treatment (hot vapour or hot water), cold treatments, insecticidal dipping, or irradiation (Armstrong and Couey, 1989). Irradiation is not accepted in most countries and fumigation is a hazardous operation. Heat treatment tends to reduce the shelf life of most fruits and so the most effective method of regulatory control is to preferentially restrict imports of a given fruit to areas free of fruit fly attack.
Cultural Control and Sanitary Methods
One of the most effective control techniques against fruit flies in general is to wrap fruit, either in newspaper, a paper bag, or in the case of long/thin fruits, a polythene sleeve. This is a simple physical barrier to oviposition but it has to be applied well before the fruit is attacked. Little data is available on the attack time for most fruits but few Bactrocera spp. attack prior to ripening.
Although cover sprays of entire crops are sometimes used, the use of bait sprays is both more economical and more environmentally acceptable. A bait spray consists of a suitable insecticide (e.g. malathion) mixed with a protein bait. Both males and females of fruit flies are attracted to protein sources emanating ammonia and so insecticides can be applied to just a few spots in an orchard and the flies will be attracted to these spots. The protein most widely used is hydrolysed protein, but some supplies of this are acid hydrolysed and so highly phytotoxic. Smith and Nannan (1988) have developed a system using autolysed protein. In Malaysia this has been developed into a very effective commercial product derived from brewery waste.
The males of most pest species of Bactrocera are attracted to either cue lure (4-(p-acetoxyphenyl)-2-butanone) or to methyl eugenol (4-allyl-1,2-dimethoxybenzene). Males of B. tau are attracted to cue lure. On a small scale many farmers use male suppression as a control technique; however, with flies attracted over a few hundred metres the traps may be responsible for increasing the fly level (at least of males) on a crop as much as for reducing it. However, the technique has been used as an eradication technique (male annihilation), in combination with bait (Bateman, 1982).
Early Warning Systems
Many coutries that are free of Bactrocera spp., e.g. USA (California and Florida) and New Zealand maintain a grid of methyl eugenol and cue lure traps, at least in high risk areas (ports and airports) if not around the entire climatically suitable area. The trap used will usually be modelled on the Steiner trap (White and Elson-Harris, 1994).
Monitoring is largely carried out by traps (as above) set in areas of infestation. However, there is evidence that some fruit flies have different host preferences in different parts of their range and host fruit surveys should also be considered as part of the monitoring process.
ReferencesTop of page
Allwood AJ; Chinajariyawong A; Kritsaneepaiboon S; Drew RAI; Hamacek EL; Hancock DL; Hengsawad C; Jipanin JC; Jirasurat M; Krong CK; Leong CTS; Vijaysegaran S, 1999. Host plant records for fruit flies (Diptera: Tephritidae) in Southeast Asia. Raffles Bulletin of Zoology, 47(Supplement 7):1-92; 26 ref.
Armstrong JW; Couey HM, 1989. Control; fruit disinfestation; fumigation, heat and cold. In: Robinson AS, Hooper G, eds. Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests. Amsterdam, Netherlands: Elsevier, 3(B):411-424.
Baimai V; Phinchongsakuldit J; Sumrandee C, 2000. Cytological evidence for a complex of species within the taxon Bactrocera tau (Diptera: Tephritidae) in Thailand. Biological Journal of the Linnean Society, 69(3):399-409; 20 ref.
Baker RT; Cowley JM, 1991. A New Zealand view of quarantine security with special reference to fruit flies, In: Vijaysegaran S, Ibrahim AG, eds. First International Symposium on Fruit Flies in the Tropics, Kuala Lumpur, 1988. Kuala Lumpur, Malaysia: Malaysian Agricultural Research and Development Institute, 396-408.
Bateman MA, 1982. III. Chemical methods for suppression or eradication of fruit fly populations, In: Drew RAI, Hooper GHS, Bateman MA eds. Economic Fruit Flies of the South Pacific Region. 2nd edn. Brisbane, Australia: Queensland Department of Primary Industries, 115-128.
Batra HN, 1968. Biology and bionomics of Dacus (Zeugodacus) hageni de Meijere (= D. caudatus Fabr.). Indian Journal of Agricultural Science, 38:1015-1020.
Christenson LD; Foote RH, 1960. Biology of fruit flies. Annual Review of Entomology, 5:171-192.
David KJ; Kumar ARV; Srinivasan Ramani, 2008. Distribution of Bactrocera Macquart (Diptera: Tephritidae) in Kerala with special reference to the Western Ghats. Journal of the Entomological Research Society, 10(2):55-69. http://www.entomol.gazi.edu.tr/Jersinfo.htm
Fletcher BS, 1989. Ecology; life history strategies of tephritid fruit flies, In: Robinson AS, Hooper G, eds. Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests. Amsterdam, Holland: Elsevier, 3(B):195-208.
Fletcher BS, 1989. Movements of tephritid fruit flies. In: Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests [ed. by Robinson, A. S., Hooper, G.]. Amsterdam, The Netherlands: Elsevier Science Publishers, 209-219.
Hardy DE, 1973. The fruit flies (Tephritidae - Diptera) of Thailand and bordering countries. Pacific Insects Monograph, 31:1-353.
Hardy DE, 1974. The fruit flies of the Philippines (Diptera: Tephritidae). Pacific Insects Monograph, No. 32:266 pp.
Hardy DE, 1982. The Dacini of Sulawesi (Diptera: Tephritidae). Treubia, 28:173-241.
Hardy DE, 1983. The fruit flies of the genus Dacus Fabricius of Java, Sumatra and Lombok, Indonesia (Diptera: Tephritidae). Treubia, 29:1-45.
Hasyim A; Muryati; Istianto M; Kogel WJde, 2007. Male fruit fly, Bactrocera tau (Diptera; Tephritidae) attractants from Elsholtzia pubescens Bth. Asian Journal of Plant Sciences, 6(1):181-183. http://www.ansinet.org/ajps
Wang Xing-Jian, 1998. The fruit flies (Diptera: Tephritidae) of the East Asian region. Acta Zootaxonomica Sinica, 21(supplement):1-338.
Wang ZeLe; Liu YingHong; Liu Hong; Zhang ChangLun; Wang ZiYing, 2007. Partial sequences on mtDNA 16S rRNA and phylogeny in 26 populations of Bactrocera tau in Chongqing. Chinese Bulletin of Entomology, 44(4):556-561. http://kczs.chinajournal.net.cn
Waterhouse DF, 1993. The Major Arthropod Pests and Weeds of Agriculture in Southeast Asia. ACIAR Monograph No. 21. Canberra, Australia: Australian Centre for International Agricultural Research, 141 pp.
Weldon CW; Schutze MK; Karsten M, 2014. Trapping to monitor tephritid movement: results, best practice, and assessment of alternatives. In: Trapping and the detection, control, and regulation of Tephritid fruit flies: lures, aarea-wide programs, and trade implications [ed. by Shelly T, Epsky N, Jang EB, Reyes-Flores J, Vargas R]. New York, USA: Springer, 175-217.
Wharton RA; Gilstrap FE, 1983. Key to and status of opiine braconid (Hymenoptera) parasitoids used in biological control of Ceratitis and Dacus s.l. (Diptera: Tephritidae). Annals of the Entomological Society of America, 76(4):721-742
Wharton RH, 1989. Control; classical biological control of fruit-infesting Tephritidae, In: Robinson AS, Hooper G, eds. Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests 3(B). Amsterdam, Netherlands: Elsevier, 303-313.
Zhang HongMei; Pan YaQin; Wei DiGong; Wu JunXiang, 2004. Random amplified polymorphic DNA in four species of fruit flies (Diptera: Tephritidae) distributed commonly in Shaanxi Province, China. Entomotaxonomia, 26(1):59-63.
Distribution MapsTop of page
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