Preferred name: Bactrocera minax
Authority: (Enderlein)
Taxonomic position: Animalia: Arthropoda: Hexapoda: Insecta: Diptera: Tephritidae
Other scientific names: Bactrocera citri (Chen), Callantra minax (Enderlein), Dacus citri (Chen), Mellesis citri Chen, Polistomimetes minax Enderlein, Tetradacus citri (Chen)
Common names in English: Chinese citrus fly
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Notes on taxonomy and nomenclature EPPO Categorization: A1 list
view more categorizations online...
EPPO Code: DACUCT

B. minax is found exclusively on Rutaceae, such as Citrus and Fortunella. Xia et al. (2018) reports that in China most surveys indicate that mainly sweet oranges are heavily infested, although some surveys have shown high infestation occasionally in pomelo and sour oranges. In Bhutan mandarins are heavily infested (Dorji et al., 2006). The USDA Compendium of Fruit Fly Host Information (CoFFHI) (Chang et al., 2018) provides an extensive host list with detailed references.

Host list: Citrus maxima, Citrus medica, Citrus reticulata, Citrus trifoliata, Citrus x aurantiifolia, Citrus x aurantium var. deliciosa, Citrus x aurantium var. paradisi, Citrus x aurantium var. sinensis, Citrus x aurantium var. tangerina, Citrus x aurantium var. unshiu, Citrus x aurantium, Citrus x junos, Citrus x limon, Citrus x nobilis, Fortunella crassifolia, Fortunella japonica, Fortunella margarita

The known distribution of B. minax is restricted to northeastern India, Bhutan, Nepal, and southern China. The record from Donghai County in Jiangsu, China is uncertain according to Hancock & Drew (2018).

Asia: Bhutan, China (Chongqing, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi, Shaanxi, Sichuan, Yunnan), India (Sikkim, West Bengal), Nepal, Taiwan

Bactrocera minax is an univoltine species (only one generation each year) and goes into diapause in the soil as a pupa during winter (Dong et al., 2013). The overwintering stage lasts about 160-170 days (Fan et al., 1994) and a period of at least three months of winter conditions is required for successful diapause development and termination (Dong et al., 2013). Diapause termination is synchronized with fruit development, with adult emergence between April and May and adult life span between one and three months (Xia et al., 2018). Oviposition takes place in June-July (Dorji et al., 2006), and eggs are laid below the skin of young host fruits. Three larval stages develop inside the fruit, feeding on the plant tissue. A review on this species in China is given by Xia et al. (2018), while details of development in mandarin in Bhutan is given by Dorji et al. (2006). Additional information is given in Zhang (1989), Fan et al. (1994), and Dong et al. (2013). In general, B. minax has a similar biology to B. tsuneonis but adults of B. tsuneonis can be found over a longer time in the field.

Symptoms

Attacked fruit have tiny oviposition punctures, but these and other symptoms of damage are often difficult to detect in the early stages of infestation. Considerable damage may occur inside the fruit before symptoms are visible externally, often as networks of tunnels accompanied by rotting.

Morphology

Larva

Fruit fly larvae in general have a typical shape, i.e., cylindrical maggot-shape, elongate, anterior end narrowed and somewhat recurved ventrally, with anterior mouth hooks, and flattened caudal end. Their length varies from 5 to 15 mm. Identification to species level is not possible based on larvae. A key for the 3rd-instar larvae is available in White & Elson- Harris (1992) and is useful for an identification to the genus level. The larva of B. minax is also described in some detail by White & Elson-Harris (1992).

Adult

Redescription, as given by Drew & Romig (2013). 

Male
Head. Red-brown, fulvous along eye margins and with small dark fuscous areas around bases of orbital setae and on anteromedial hump; orbital setae black: 1 superior, 2 inferior; lunule dark fuscous. Ocellar triangle black. Vertex red-brown. Face fulvous with a pair of large elongate black spots filling most of antennal furrow. Occiput red-brown, fulvous along eye margins; occipital row with 1-4 weak black setae. Antennae with all segments red-brown. 

Thorax. Scutum red-brown with a mottled appearance from dorsoventral flight muscles and irregular dark fuscous patterns and particularly with a narrow medial longitudinal dark fuscous line running from anterior point of medial postsutural yellow vitta to anterior margin of scutum. Pleural areas red-brown with fuscous along anterior and posterior margins of mesopleural stripe. Yellow markings as follows: postpronotal lobes; notopleura; a lateral yellow band running from posterior margin of postpronotal lobes towards notopleuron but finishing before the notopleuron; a broad mesopleural stripe reaching the anterior notopleural seta dorsally, extending to the katepisternum as a large transverse spot, anterior margin slightly convex; anatergite (posterior apex red-brown); anterior two-thirds katatergite (remainder red-brown); two medium-width parallel-sided lateral postsutural vittae ending at intra-alar seta and turned slightly inwards along notopleural suture; a broad medial postsutural vitta broadly rounded posteriorly at level of posterior supraalar. seta and narrowing to a point to end anteriorly before level of notopleural suture. Postnotum red-brown. Scutellum yellow except for narrow red-brown basal band. Setae: 2 scutellar, 1 intra-alar, 1 posterior supra-alar, 1 mesopleural, 1 notopleural, 2 scapular; prescutellar and anterior supra-alar absent.

Legs. Femora fulvous except for small areas of fuscous around bases of all femora and larger areas of fuscous to dark fuscous around apices of mid and hind femora ; fore tibiae fuscous to dark fuscous basally to fulvous apically, hind tibiae fuscous to dark fuscous; all tarsal segments fulvous; mid tibiae each with an apical black spur.

Wings. Length 10.8 mm; cells bc and c fuscous; microtrichia in outer half of cell c only; remainder of wings colourless except fuscous cell sc, broad fuscous costal band overlapping R4+5 and having a distinct dark fuscous spot within apex, a distinct anal streak absent but with pale fuscous within cell cup; no dense aggregation of microtrichia around A1+CuA2; supernumerary lobe weak.

Abdomen. Elongate oval and petiolate; terga free; pecten present on tergum III. Tergum I and sterna I and II longer than wide. Terga I and II fulvous with narrow fuscous to dark fuscous lateral margins and a broad medial longitudinal dark fuscous band that is diffuse on the lateral margins; terga III-V variable from fulvous to red-brown and with a dark fuscous to black ‘T’ pattern consisting of a broad transverse band across anterior margin of tergum III which widens to cover lateral margins and a narrow medial longitudinal band over all three terga but ending before posterior margin of tergum III, fuscous to dark fuscous anterolateral corners on terga IV and V (in some specimens the dark patterns on terga III-V are paler and reduced to a fuscous medial longitudinal band over all three terga and pale fuscous anterolateral corners on terga IV and V). A pair of oval fulvous to red-brown shining spots on tergum V. Posterior lobe of surstylus short, sternum V with a slight concavity on posterior margin. Abdominal sterna variable from red-brown to fuscous.  

Female
As for male except pecten of cilia on abdominal tergum III absent, ovipositor basal segment red-brown, broadly conical in transverse cross section at base and narrowing and circular in transverse cross section towards apex, and extremely long; ratio of length of oviscape to length of tergum V, 2.7:1; apex of piercer needle-shaped.

B. minax is morphologically similar to B. tsuneonis (Drew & Romig, 2013), but lacking anterior supra-alar setae. It has an incomplete lateral yellow band between the postpronotal lobe and the notopleuron and the female has a longer ovipositor (aculeus 3.7-5.0 mm long), with a needle-shaped apex.  Full details of the separation of these species were given by White & Wang (1992) and Drew & Romig (2013). Hancock & Drew (2019) provide an identification key for all representatives of the subgenus Tetradacus. 

DNA barcoding 

In the Barcode of Life Data Systems (BOLD), B. minax only forms monospecific Barcoding Index Number Systems (BINs) including representatives from the geographical distribution of this species. For this reason, DNA barcoding might be considered as a suitable tool for the molecular identification of this species. Sequences are available in the Barcode of Life Data Systems (BOLD) and in EPPO-Q-Bank.

Detection and inspection methods

Though most Bactrocera spp. can be monitored by traps baited with male lures, B. minax is not known to be attracted to any male lure. A weak attraction of both sexes to methyl eugenol was reported by Drew et al. (2007). However, this appears to be a seasonal effect, related to the fly’s sexual maturation and mating (Royer, 2015) and considered incidental by Hancock & Drew (2018). Both sexes can be monitored by traps baited with protein-based attractants (Xia et al., 2018). Chen et al. (2017) report the use of fruit mimic traps as effective in monitoring of B. minax. Detection is also possible by examination of fruit for oviposition punctures and then rearing the larvae through to the adult stage.

Transport of infested fruits is the main mean of movement and dispersal to previously uninfested areas. Adult flight can also result in dispersal but previous citations of long (50-100 km) dispersal movements for Bactrocera spp. are unsubstantiated according to a recent review by Hicks et al. (2019). Dispersal up to 2 km is considered more typical.

Economic impact

B. minax is stenophagous, only attacking citrus fruits. It is a serious pest of citrus in parts of China (Zhang, 1989) but the severity and economic impact can differ among the different regions (Xia et al., 2018).

Control

Management for this species includes the general control measures for Bactrocera spp. (see Vargas et al. 2015 for an overview of management options). Specific Integrated Pest Management (IPM) and other management options applied in Bhutan and China are reviewed respectively in Dorji et al. (2006) and Xia et al. (2018). These include sanitation (to gather all fallen and infested host fruits, and destroy them), and raking or shallow plowing of the soil during winter (to expose the pupae). Insecticidal protection is possible by using a cover spray or a bait spray. Bait sprays work on the principle that both male and female tephritids are strongly attracted to a protein source from which ammonia emanates. Bait sprays have the advantage over cover sprays in that they can be applied as a spot treatment so that the flies are attracted to the insecticide and there is minimal impact on natural enemies and beneficials. Xia et al. (2018) give a review of comparative testing of different food-based lures against B. minax. Area-wide control, using protein bait spraying, was recently conducted in Nepal (Adhikari et al., 2020). Wang & Luo (1995) report the use of Sterile Insect Technique (SIT ) on orange crops in Guizhou Province, China in 1993 and 1994 resulting in a reduction from over 5% infestation to about 0.1% by releasing 1 million sterile males (obtained from natural populations). For more details on this and other SIT applications in China, see Xia et al. (2018). The main current drawback for mass rearing of B. minax for SIT is the obligatory diapause. 

Phytosanitary risk

Citrus species are important crops in the EPPO region. B. minax is a known pest of Citrus in the area where it is present. It can be moved in trade with infested fruit. Although no detailed study was made on climatic suitability of the EPPO region for this species, B. minax is known to occur in temperate areas. Transient populations could also have negative impacts on export of host fruit from the EPPO region. The EFSA Panel on Plant Health, in their Pest Categorization of non-EU Tephritidae (Bragard et al. 2020) placed B. minax on the list of fruit flies that satisfy the criteria to be regarded as a potential Union quarantine pest for the EU.

Consignments of fruits of Citrus and Fortunella from countries where B. minax occurs should be inspected for symptoms of infestation and those suspected should be cut open in order to look for larvae. Possible measures include that such fruits should come from an area where B. minax does not occur, or from a place of production found free from the pest by regular inspections in the 3 months before harvest. 

In China both irradiation and cold treatment have been explored as phytosanitary measures. Irradiation required 50-90 Gy to reach zero adult emergence (Gao et al., 1999; Zhao et al., 1995). No specific treatment schedules for cold treatment have been developed but given the cold tolerance of B. minax it is uncertain if schedules for other fruit flies (such as Ceratitis capitata) will be adequate.

Plants of citrus transported with roots from countries where B. minax occurs should be free from soil, or the soil should be treated against puparia. The plants should not be bearing fruits. Citrus plants are in any case prohibited from importation in many countries because of other quarantine pests.

Adhikari D, Thapa RB, Joshi SL, Lian H & Du JJ (2020) Area-wide control program of Chines citrus fly Bactrocera minax (Enderlein) in Sindhuli, Nepal. American Journal of Agricultural and Biological Sciences 15, 1-7.

EFSA PLH Panel (EFSA Panel on Plant Health), Bragard C, Dehnen-Schmutz K, Di Serio F, Gonthier P, Jacques MA, Jaques Miret JA, Justesen AF, Magnusson CS, Milonas P, Navas-Cortes JA, Parnell S, Potting R, Reignault PL, Thulke HH, Van der Werf W, Vicent Civera A, Yuen J, Zappalà L, Bali EM, Papadopoulos N, Papanastassiou S, Czwienczek E & MacLeod A (2020) Pest categorization of non-EU Tephritidae. EFSA Journal 18: 5931, 62pp. https://doi.org/10.2903/j.efsa.2020.5931

Chang CL, Liquido NJ, Nakamichi KAA & Ching AJ (2018) Host Plant Records of the Chinese Citrus Fruit Fly (柑橘大实蝇), Bactrocera minax (Enderlein) (Diptera: Tephritidae). Version 1.0 February 06, 2018. United States Department of Agriculture, 22pp. Available online at https://coffhi.cphst.org/ (accessed  12/04/2020)

Chen ZZ, Deng AS, Zhu Q Chen WB, Xu XM, Zheng B & Niu CY (2017) Assessing attracting and killing effects of the spherical traps against Chinese citrus fly, Bactrocera minax. Journal of Huazhong Agricultural University 36, 33-37.

Dong YC, Wang ZJ, Clarke AR, Pereira R, Desneux N & Niu CY (2013) Pupal diapause development and termination is driven by low temperature chilling in Bactrocera minax. Journal of Pest Science 86, 429-436.

Dorji C, Clarke AR, Drew RAI, Fletcher BS, Loday P, Mahat K, Raghu S & Romig MC (2006) Seasonal phenology of Bactrocera minax (Diptera: Tephritidae) in western Bhutan. Bulletin of Entomological Research 96, 531-538.

Drew RAI & Romig MC (2013) Tropical Fruit Flies (Tephritidae: Dacinae) of South-East Asia.CAB International, Wallingford (UK). 

Drew RAI, Romig MC & Dorji C (2007) Records of dacine fruit flies and new species of Dacus (Diptera: Tephritidae) in Bhutan. The Raffles Bulletin of Zoology 55, 1-21.

EPPO/CABI (1996) Bactrocera tsuneonis. In: Quarantine pests for Europe. 2nd edition (Ed. by Smith, I.M.; McNamara, D.G.; Scott, P.R.; Holderness, M.). CAB INTERNATIONAL, Wallingford, GB.

Fan JA, Zhao XQ & Zhu J (1994) [A study on cold-tolerance and diapause in Tetradacus citri Chen]. Journal of Southwest Agricultural University 16, 532-534. (in Chinese)

Gao MX, Wang C, Li SR & Tang ZX (1999) [The study of irradiation on pest in orange and chestnut.] Plant Quarantine 13, 197-1999. (in Chinese)

Hancock DL & Drew RAI (2018) A review of the subgenera Apodacus Perkins, Hemizeugodacus Hardy, Neozeugodacus May, stat. rev., Semicallantra Drew and Tetradacus Miyake of Bactrocera Macquart (Diptera: Tephritidae: Dacinae). Australian Entomologist 45, 105-132.

Hancock DL & Drew RAI (2019) Further notes on subgenus Tetradacus Miyake of Bactrocera Macquart (Diptera: Tephritidae: Dacinae), with a revised key to species. Australian Entomologist 46, 43-46.

Hicks CB, Bloem K, Pallipparambil GR & Hartzog HM (2019) Reported long-distance flight of the invasive Oriental fruit fly and its trade implications. In Area-Wide Management of Fruit Flies (eds Pérez-Staples D, Diaz-Fleischer F, Montoya P. & Vera MT), pp. 9-26. CRC Press, Boca Raton (US) 

Royer JE (2015) Responses of fruit flies (Tephritidae: Dacinae) to novel male attractants in north Queensland, Australia, and improved lures for some pest species. Austral Entomology 54, 411-426.

Vargas RI, Pinero JC & Leblanc L (2015) An overview of pest species of Bactrocera fruit flies (Diptera: Tephritidae) and the integration of biopesticides with other biological approaches for their management with a focus on the Pacific region. Insects 6, 297-318.

Wang XJ & Luo YL (1995) [Advanced study on Bactrocera minax.] Chinese Bulletin of Entomology 32, 310-315. (in Chinese)

White IM & Elson-Harris MM (1992) Fruit flies of economic significance; their identification and bionomics. CAB International, Wallingford (GB).

White IM & Wang XJ (1992) Taxonomic notes on some dacine (Diptera: Tephritidae) fruit flies associated with citrus, olives and cucurbits. Bulletin of Entomological Research 82, 275-280.

Xia Y, Ma X, Hou B & Ouyang G (2018) A review of Bactrocera minax (Diptera: Tephritidae) in China for purpose of safeguarding. Advances in Entomology 6, 35-61.

Zhang Y (1989) Citrus fruit flies of Sichuan Province (China). Bulletin OEPP/EPPO Bulletin 19, 649-654.

Zhao XQ, Fan JA, Xie CL, Qin Z, Li G, Zhu J, Zeng DB & Kong FC (1995) [Gamma irradiation as a quarantine treatment against Tetradacus citri in pomelo and orange fruits.] Journal of Southwest Agricultural University 17, 126-129. (in Chinese)

CABI resources used when preparing this datasheet

CABI invasive species compendium: https://www.cabi.org/isc/datasheet/8726

This datasheet was extensively revised in 2020 by Dr M. de Meyer. His valuable contribution is gratefully acknowledged.

EPPO (2024) Bactrocera minax. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-26)

This datasheet was first published in 1992 in 'Quarantine Pests for Europe' as Bactrocera spp. (non-European), then as 'Bactrocera minax' in the second edition of the book in 1997, and revised in 2020. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1992/1997) Quarantine Pests for Europe (1^st and 2^nd edition). CABI, Wallingford (GB).