Resolving the Bactrocera dorsalis complex

Pest fruit flies of the Bactrocera dorsalis complex dominate NAQS, AQIS and industry target lists. Three species within the complex (B. dorsalis s.s., B. papayae and B. philippinensis) are category two pests in the Deed. Unfortunately, despite their importance, these three species cannot be adequately resolved from each other, nor from endemic, non-regulated fruit fly species. Also, a fourth non-Australian pest species, B. carambolae, is closely related to these three species and is morphologically and genetically similar.

Project CRC20115 is simultaneously bringing together, for the first time, a series of parallel data sets focussing on molecular, morphological, and behavioural information relating to each of these four pest species. The chief objective of this study is to retest their original classification to determine the validity of their taxonomic identities, and whether the current classification is biologically meaningful. Once species boundaries have been resolved, definitive molecular markers will be developed.

Molecular characterisation is being achieved by amplifying and sequencing six genetic markers from both the nuclear (ITS1, ITS2, CAD) and mitochondrial genomes (COI, ND4-2), together with transcriptome analysis on, so far, three of the four pest species. Geometric morphometric shape analysis on wings is being applied to determine the capacity of the technique to achieve fine-scale resolution between populations or species. Behavioural aspects specific to the mating systems of the four species are being examined, mainly via mating compatibility studies being undertaken at FAO/IAEA research laboratories situated in Seibersdorf, Austria.

Results so far demonstrate that, similar to previous studies on these species, B. carambolae is genetically the most distinct species from the remaining three. Geometric morphometric data based on DEEDI collection material can resolve differences in wing shape variation among different populations of the species and is a promising tool for further development. Ongoing mating compatibility studies have so far revealed that B. carambolae and B. dorsalis exhibit relatively high levels of mating isolation under field-cage conditions (remaining species yet to be tested).

Remaining work for this project is to:

a) complete the collection of sequence data for all selected specimens;

b) extend the use of shape analysis to de novo collected material; and

c) complete mating compatibility studies to include recently acquire live material of B. philippinensis and B. papayae.

Once collected, this data will be analysed together to provide a recommendation as to the relationships between these pest species and their subsequent classification to be applied to trade and quarantine purposes. This project is now intimately tied and working in collaboration with the FAO/IAEA Coordinated Research Project, ‘Resolution of cryptic species complexes of tephritid pests to overcome constraints to SIT applications and international trade’.