Bactrocera papayae Drew & Hancock, Bactrocera philippinensis Drew & Hancock, Bactrocera carambolae Drew & Hancock, and Bactrocera invadens Drew, Tsuruta & White are four horticultural pest tephritid fruit fly species that are highly similar, morphologically and genetically, to the destructive pest, the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). This similarity has rendered the discovery of reliable diagnostic characters problematic, which, in view of the economic importance of these taxa and the international trade implications, has resulted in ongoing difficulties for many areas of plant protection and food security. Consequently, a major international collaborative and integrated multidisciplinary research effort was initiated in 2009 to build upon existing literature with the specific aim of resolving biological species limits among B. papayae, B. philippinensis, B. carambolae, B. invadens and B. dorsalis to overcome constraints to pest management and international trade. Bactrocera philippinensis has recently been synonymized with B. papayae as a result of this initiative and this review corroborates that finding; however, the other names remain in use. While consistent characters have been found to reliably distinguish B. carambolae from B. dorsalis, B. invadens and B. papayae, no such characters have been found to differentiate the latter three putative species. We conclude that B. carambolae is a valid species and that the remaining taxa, B. dorsalis, B. invadens and B. papayae, represent the same species. Thus, we consider B. dorsalis (Hendel) as the senior synonym of B. papayae Drew and Hancock syn.n. and B. invadens Drew, Tsuruta & White syn.n. A redescription of B. dorsalis is provided. Given the agricultural importance of B. dorsalis, this taxonomic decision will have significant global plant biosecurity implications, affecting pest management, quarantine, international trade, postharvest treatment and basic research. Throughout the paper, we emphasize the value of independent and multidisciplinary tools in delimiting species, particularly in complicated cases involving morphologically cryptic taxa. Bactrocera (Bactrocera) dorsalis (Hendel)

The phytophagous insects of the Tephritidae family offer different case histories of successful invasions. An example is Bactrocera dorsalis sensu stricto, the oriental fruit fly which has been recognized as a key pest of Asia and the Pacific. It is known to have the potential to establish adventive populations in various tropical and subtropical areas. Despite the economic risk associated with a putative stable presence of this fly, the genetic aspects of its invasion process have remained relatively unexplored. Using microsatellite markers we have investigated the population structure and genetic variability in 14 geographical populations across the four areas of the actual species range: Far East Asia, South Asia, Southeast Asia and the Pacific Area. Results of clustering and admixture, associated with phylogenetic and migration analyses, were used to evaluate the changes in population genetic structure that this species underwent during its invasion process and establishment in the different areas. The colonization process of this fly is associated with a relatively stable population demographic structure, especially in an unfragmented habitat, rich in intensive cultivation such as in Southeast Asia. In this area, the results suggest a lively demographic history, characterized by evolutionary recent demographic expansions and no recent bottlenecks. Cases of genetic isolation attributable to geographical factors, fragmented habitats and/or fruit trade restrictions were observed in Bangladesh, Myanmar and Hawaii. Regarding the pattern of invasion, the overall genetic profile of the considered populations suggests a western orientated migration route from China to the West.

Two tephritid species namely the oriental fruit fly Bactrocera dorsalis Hendel and the guava fruit fly Bactrocera correcta Bezzi are considered to be the key insect pests of fruit production in Thailand, causing yield loss and quality degradation. This leads to poor commercialization in domestic markets and quarantine restrictions from importing countries. A decade of effective cooperation between Thailand's Department of Agricultural Extension (DOAE), the International Atomic Energy Agency (IAEA), and the Food and Agriculture Organization of the United Nations (FAO) has resulted in the implementation of an area-wide integrated fruit fly management programme which includes a sterile insect technique (SIT) component. The programme consists of two distinctive pilot areas with associations of smallscale mango growers covering 70 square kilometres in the Ratchaburi (western) and Pichit (northern) Provinces. The ongoing programme is aimed at controlling B. dorsalis and B. correcta through monitoring, orchard sanitation, selective application of bait sprays, and the release of sterile flies. Both species are mass-reared and sterilized at a facility located in Pathumthani Province following standard operational procedures described in this paper. The average weekly production during the mango season is 20 million B. dorsalis and 10 million B. correcta. After sterilization the pupae are transported weekly to the pilot areas, reared to the adult stage and ground-released at fixed release sites. Quality of the released sterile flies is monitored through the use of a trapping network to measure their distribution and abundance, whilst the success of the control is monitored using periodic fruit sampling to assess the percentage infestation. The integrated approach has been effective in controlling fruit flies by reducing damage from over 80% before programme implementation to an average of less than 3.6% in Ratchaburi Province in the past five years (2000 to 2004). Meanwhile, in Pichit Province where the control programme has been carried out for only two years (2003 and 2004), the infestation has been reduced from 42.9 to 15.5%. This preharvest suppression, combined with postharvest risk mitigation measures, has opened the possibility for exports of mango produced in these selected pilot areas to some of the most stringent and lucrative markets such as Japan. An economic feasibility study conducted in 2002 clearly shows that fruit fly control in Thailand using an integrated area-wide approach with an SIT component could be expanded to other production areas with significant economic returns.

Abstract. The oriental fruit fly, Bactrocera dorsalis, is a key economic insect pest reducing fruit yield and generating constraints in the international market. The application of the sterile insect technique (SIT) continues to reveal areas where new technologies can improve the effectiveness of fruit fly control. One such advancement concerns insect strains. In the present study, a mass-reared strain of the fly with a translocation-based genetic sexing character (Salaya1) based on a brown-white pupal colour dimorphism was genetically characterized using 11 microsatellite DNA markers. Subsequently, these markers were used to evaluate the maintenance of genetic variability in the strain under mass-rearing conditions. Mating competitiveness of this strain was also tested in field cages. Two of the newly characterized Y-pseudo-linked microsatellite markers were used for strain identification in field monitoring traps. The strain was also validated in a pilot integrated pest management (IPM) programme using male-only SIT in a fruit orchard. The programme resulted in the suppression of the fruit fly population.

Seventeen novel microsatellite markers were isolated and characterized from an enriched DNA library of the pest species Bactrocera dorsalis sensu stricto . The polymorphism of these loci was tested in individual fruit flies from a Thai mass-rearing strain and three wild Asian populations: two from Thailand and one from Myanmar. Allele numbers per locus ranged from two to 15. In the natural populations, a high level of polymorphism was detected in all loci suggesting the usefulness of these markers to quantify the genetic variation in this highly invasive insect.

Doublesex (dsx) is a double-switch gene at the bottom of the somatic sex-determination hierarchy which regulates sexual dimorphism in many insects. Here, Drosophila melanogaster homologues of dsx were isolated in two Bactrocera species, the oriental fruit fly, B. dorsalis, and the guava fruit fly, B. correcta. Results of RT-PCR analysis suggests that both the B. dorsalis dsx (Bd1dsx) and B. correcta dsx (Bcdsx) genes are transcribed and sex-specifically spliced in accordance with the Drosophila sex-specific splicing mechanism. The cDNA sequences shared a high degree of similarity at the nucleotide level among the Bactrocera species. Structurally conserved domains for DNA-binding and oligomerization were observed in all transcripts suggesting that their proteins function as transcriptional factors for downstream sex-specific gene expression. A purine-rich element (PRE) and four repeat elements (dsxRE) for TRA/TRA-2 binding sites were also found in the 3' untranslated regions (UTR) of both the female Bd1dsx and Bcdsx mRNAs. Notably, a putative core promoter was revealed in Bd1dsx, being probably the first dsx promoter discovered in the tephritid flies.

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a key pest that causes reduction of the crop yield within the international fruit market. Fruit flies have been suppressed by two Area-Wide Integrated Pest Management programs in Thailand using Sterile Insect Technique (AW-IPM-SIT) since the late 1980s and the early 2000s. The projects' planning and evaluation usually rely on information from pest status, distribution, and fruit infestation. However, the collected data sometimes does not provide enough detail to answer management queries and public concerns, such as the long term sterilization efficacy of the released fruit fly, skepticism about insect migration or gene flow across the buffer zone, and the re-colonisation possibility of the fruit fly population within the core area. Established microsatellite DNA markers were used to generate population genetic data for the analysis of the fruit fly sampling from several control areas, and non-target areas, as well as the mass-rearing facility. The results suggested limited gene flow (m < 0.100) across the buffer zones between the flies in the control areas and flies captured outside. In addition, no genetic admixture was revealed from the mass-reared colony flies from the flies within the control area, which supports the effectiveness of SIT. The control pests were suppressed to low density and showed weak bottleneck footprints although they still acquired a high degree of genetic variation. Potential pest resurgence from fragmented micro-habitats in mixed fruit orchards rather than pest incursion across the buffer zone has been proposed. Therefore, a suitable pest control effort, such as the SIT program, should concentrate on the hidden refuges within the target area.

BackgroundBactrocera dorsalis s.s. (Hendel) and B. papayae Drew & Hancock, are invasive pests belonging to the B. dorsalis complex. Their species status, based on morphology, is sometimes arguable. Consequently, the existence of cryptic species and/or population isolation may decrease the effectiveness of the sterile insect technique (SIT) due to an unknown degree of sexual isolation between released sterile flies and wild counterparts. To evaluate the genetic relationship and current demography in wild populations for guiding the application of area-wide integrated pest management using SIT, seven microsatellite-derived markers from B. dorsalis s.s. and another five from B. papayae were used for surveying intra- and inter-specific variation, population structure, and recent migration among sympatric and allopatric populations of the two morphological forms across Southern Thailand and West Malaysia.ResultsBasic genetic variations were not significantly different among forms, populations, and geographical areas (P > 0.05). Nonetheless, two sets of microsatellite markers showed significantly different levels of polymorphisms. Genetic differentiation between intra- and inter-specific differences was significant, but low. Seventeen populations revealed three hypothetical genetic clusters (K = 3) regardless of forms and geographical areas. The genetic structure of sympatric populations slightly changed during the different years of collection. Recent gene flow (m ≥ 0.10) was frequently detected whether samples were sympatric or allopatric. Ninety-five of 379 individuals distributed across the given area were designated as recent migrants or of admixed ancestry. As a consequence of substantial migration, no significant correlation between genetic and geographic distances was detected (R2 = 0.056, P = 0.650).ConclusionsAccording to the 12 microsatellite variations, weak population structure and recent gene flow suggest that there is no status for cryptic species between B. dorsalis s.s. and B. papayae forms in Southern Thailand and West Malaysia. Both forms can be treated as a single target pest for the SIT program in an area-wide sense. Additionally, the result of species identification based on molecular data and morphological character are not congruent. The use of independent, multiple approaches in the characterization of the target population may ensure the effectiveness and feasibility of SIT-based control in the target area.