Zeugodacus tau species complex

Taxonomy

The 20-species Z. tau species complex sensu Drew and Romig 2016Drew and Romig 2016:
Drew RAI, Romig MC, 2016. Keys to the Tropical Fruit Flies of South-East Asia. CABI Publishing, 487 pp. is not monophyletic (San Jose et al. 2018San Jose et al. 2018:
San Jose M, Doorenweerd C, Leblanc L, Barr N, Geib S, Rubinoff D, 2018. Incongruence between molecules and morphology: A seven-gene phylogeny of Dacini fruit flies paves the way for reclassification (Diptera: Tephritidae). Molecular Phylogenetics and Evolution 121: 139–149. https://doi.org/10.1016/j.ympev.2017.12.001 ) but maintained as a group here for lack of a better alternative. The following species are included:

Valid name: Zeugodacus (Zeugodacus) tau (Walker, 1849)
Preferred common name: Tau's fruit fly

Valid name: Zeugodacus (Zeugodacus) borongensis (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) flavopectoralis (Hering, 1953)
Valid name: Zeugodacus (Zeugodacus) heinrichi (Hering, 1941)
Valid name: Zeugodacus (Zeugodacus) hodgsoniae (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) isolatus (Hardy, 1973)
Valid name: Zeugodacus (Zeugodacus) javadicus (Mahmood, 1999)
Valid name: Zeugodacus (Zeugodacus) khaoyaiae (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) macrophyllae (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) okunii (Shiraki, 1933)
Valid name: Zeugodacus (Zeugodacus) pubescens (Bezzi, 1919)
Valid name: Zeugodacus (Zeugodacus) signatus (Hering, 1941)
Valid name: Zeugodacus (Zeugodacus) synnephes (Hendel, 1913)
Valid name: Zeugodacus (Zeugodacus) tapervitta (Mahmood, 1999)
Valid name: Zeugodacus (Zeugodacus) tebeduiae (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) trichosanthes (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) tricuspidatae (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) trivandrumensis (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) yalaensis (Drew & Romig, 2013)
Valid name: Zeugodacus (Zeugodacus) zahadi (Mahmood, 1999)

Zeugodacus tau, Z. tapervitta, and Z. trichosanthes have been recorded as pests of agricultural importance.

Morphology-based identification

Several members of the Z. tau species complex are morphologically very similar and can be difficult to tell apart based on morphology alone. The males of most of the species in this complex have a keel-like extension of the supernumerary lobe, and an important character to distinguish species within the complex is the presence of one versus two pairs of setae on the scutellum.

Zeugodacus tau is most similar to Z. heinrichi (distinguished by lighter sternite plates and stronger attraction to zingerone), Z. isolatus (the abdominal pattern typical of Z. isolatus is sometimes seen in Z. tau), and Z. zahadi, which is likely a synonym (Drew & Romig 2013). Zeugodacus tau has a dark spot on the front femur and dark apices on the mid and hind femur.

Zeugodacus tapervitta can be identified reliably based on morphology. Spot characters are the dark marks centrally on all femora and the yellow vitta on the scutum that taper sharply into a point posteriorly.

Zeugodacus trichosanthes can be identified reliably based on morphology. Males do not have an extended keel-shaped supernumerary lobe, and females have a trilobed ovipositor apex. All femora are yellow without dark markings.

Molecular identification

Based on Doorenweerd et al. 2024Doorenweerd et al. 2024:
Doorenweerd C, San Jose M, Leblanc L, Barr N, Geib SM, Chung AYC, Dupuis JR, Ekayanti A, Fiegalan E, Hemachandra KS, Hossain MA, Huang C, Hsu Y, Morris KY, Maryani A. Mustapeng A, Niogret J, Pham TH, Thi Nguyen N, Sirisena UGAI, Todd T, Rubinoff D, 2024. Towards a better future for DNA barcoding: Evaluating monophyly‐ and distance‐based species identification using COI gene fragments of Dacini fruit flies. Molecular Ecology Resources 24: e13987. https://doi.org/10.1111/1755-0998.13987, COI sequencing can be used to reliably identify Z. tau, provided that Z. zahadi is considered a synonym. This synonymy has not officially been established but has been suggested in Drew and Romig 2013Drew and Romig 2013:
Drew RAI, Romig MC, 2013. Tropical fruit flies of South-East Asia. CABI, 655 pp.. The nearest sister species of Z. tau is Z. cucurbitae - another major pest species but not part of the morphological Z. tau species complex.

However, a series of papers have reported COI-based host races of Z. tau in Thailand of which the taxonomic status is unclear and requires further study (Jamnongluk et al. 2003Jamnongluk et al. 2003:
Jamnongluk W, Baimai V, Kittayapong P, 2003. Molecular evolution of tephritid fruit flies in the genus Bactrocera based on the cytochrome oxidase I gene. Genetica 119: 19–25. https://doi.org/10.1023/A:1024481032579, Kunprom and Pramual 2019Kunprom and Pramual 2019:
Kunprom C, Pramual P, 2019. DNA barcoding of fruit flies (Diptera: Tephritidae) in Thailand: ambiguity, misidentification and cryptic diversity. Mitochondrial DNA Part A: DNA Mapping, Sequencing, and Analysis 30: 861–873. https://doi.org/10.1080/24701394.2019.1693550, Kitthawee and Julsirikul 2019Kitthawee and Julsirikul 2019:
Kitthawee S, Julsirikul D, 2019. Population genetic structure of Zeugodacus tau species complex in Thailand. Agricultural and Forest Entomology 21: 265–275. https://doi.org/10.1111/afe.12328, Kunprom and Pramual 2020Kunprom and Pramual 2020:
Kunprom C, Pramual P, 2020. Cryptic diversity in fruit fly, Zeugodacus isolatus (Hardy) (Diptera: Tephritidae). International Journal of Tropical Insect Science 40: 983-988. https://doi.org/10.1007/s42690-020-00156-1).

There are no COI reference sequences available for the pests Z. tapervitta and Z. trichosanthes. COI reference sequence data is available for eight of the 20 species in this morphological complex: Z. tau, Z. heinrichi, Z. isolatus, Z. khaoyaiae, Z. signatus, Z. synnephes, Z. tebeduiae, and Z. zahadi.

Distribution

Zeugodacus tau is a widespread species in Southeast Asia from India to Taiwan, and south to Indonesia. Its native range is unclear, and a lack of diversity in COI suggests a rapid population expansion in recent time (Doorenweerd et al. 2019Doorenweerd et al. 2019:
Doorenweerd C, Jose MS, Barr N, Leblanc L, Rubinoff D, 2019. Highly variable COI haplotype diversity between three species of invasive pest fruit fly reflects remarkably incongruent demographic histories. Scientific Reports 10: 742007. https://doi.org/10.1038/s41598-020-63973-x)

Zeugodacus tapervitta is only known from the Philippines, which is its presumed native distribution. Literature records of Z. tau from the Philippines are misidentified Z. tapervitta (Leblanc pers. comm.).

Zeugodacus trichosanthes has been recorded from Thailand, mainland Malaysia and the island of Java in Indonesia, which is its presumed native distribution.

Further information

Zeugodacus tau is listed as a "category B" Cucurbitaceae fruit pest in mainland Southeast Asia and south to Sumatra and Sulawesi in Vargas et al. 2015Vargas et al. 2015:
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. https://doi.org/10.3390/insects6020297. A category B pest is there defined as "polyphagous fruit pests or destructive specialists more restricted in distribution, but at elevated risk of spreading to new locations".

Zeugodacus tapervitta and Z. trichosanthes are reported as "category D" pests in Vargas et al. 2015Vargas et al. 2015:
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. https://doi.org/10.3390/insects6020297. A category D pest is there defined as "species that have been occasionally bred from commercial/edible fruit or cucurbits".