Abstract. Bactrocera correcta (Bezzi) is among the most destructive fruit fly pests of the genus Bactrocera. This species infests 62 spe cies of plants belonging 30 families, many of which are commercially important. In this study, the genetic structure, diversity and de mographic history of B. correcta in Thailand were inferred from mitochondrial cytochrome c oxidase I (COI) sequences. High genetic diversity was recorded in the 171 samples collected from 15 locations. This was due largely to the existence of two divergent lineages (I, II) revealed by median joining (MJ) network analysis. Genetic structure analysis revealed an overall low level of genetic differentia tion between populations suggesting that the flies can move freely across geographic regions. Because the host plants are commonly grown in Thailand, continuity of habitats is the factor most likely responsible for the genetic homogeneity. In addition, the recent popu lation history could also be a factor that contributed to the overall low level of the genetic structure. Mismatch distribution analysis as well as Tajima's D and Fu's F S tests detected evidence of recent demographic expansion dating back to the end of the last glaciations.

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The melon fly Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) is among the most economically important pests of fruits and fleshy vegetables. The genetic diversity, genetic structure and demographic history of Z. cucurbitae in Thailand were investigated based on mitochondrial cytochrome c oxidase I (COI) sequences. Low genetic variation was found in populations of Z. cucurbitae in Thailand, which is consistent with other studies of this species. Demographic history analysis detected a signal of population expansion dating back to 140 000 years ago, which possibly followed increases in host plants after climatic recovery of the penultimate Pleistocene glaciation. Population genetic structure analysis found that 51% of pairwise comparisons are genetically significantly different. Because populations that contributed markedly to genetic structuring possessed very low haplotype diversity, the effect of genetic drift could be a factor driving population differentiation. Comparisons of genetic differentiation between flies from different host plant species found no evidence of isolation. However, most haplotypes are unique for each host plant species, indicating that there are some degrees of isolation.

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The objectives of this study were to examine the genetic variation in fruit flies (Diptera: Tephritidae) in Thailand and to test the efficiency of the mitochondrial cytochrome c oxidase subunit I (COI) barcoding region for species-level identification. Twelve fruit fly species were collected from 24 host plant species of 13 families. The number of host plant species for each fruit fly species ranged between 1 and 11, with Bactrocera correcta found in the most diverse host plants. A total of 123 COI sequences were obtained from these fruit fly species. Sequences from the NCBI database were also included, for a total of 17 species analyzed. DNA barcoding identification analysis based on the best close match method revealed a good performance, with 94.4% of specimens correctly identified. However, many specimens (3.6%) had ambiguous identification, mostly due to intra- and interspecific overlap between members of the B. dorsalis complex. A phylogenetic tree based on the mitochondrial barcode sequences indicated that all species, except for the members of the B. dorsalis complex, were monophyletic with strong support. Our work supports recent calls for synonymization of these species. Divergent lineages were observed within B. correcta and B. tuberculata, and this suggested that these species need further taxonomic reexamination.