Population tracing analysis and overwintering of Bactrocera dorsalis (Hendel) in newly occurring areas in China

Bactrocera dorsalis (Hendel), a very destructive insect pest of many fruits and vegetables, is widespread in the tropical and subtropical zones of Asia. However, the northward extension of B. dorsalis has been reported in China recently. It is crucial to determine the origin of new populations and to investigate the invasive potential of the species. Here, we investigated B. dorsalis in Nanyang, Henan Province and Heze, Shandong Province using a combined methodological approach. We first detected the hydrogen stable isotope ratios (δ²H) of B. dorsalis samples. The results showed that the δ²H values for B. dorsalis from Nanyang were consistent with those of the local rainwater. In contrast, the samples from Heze were inconsistent with those of the rainwater in Heze. We then sequenced the complete mitochondrial cytochrome oxidase I (mtDNA COI) from the same fruit fly samples for haplotype diversity and phylogenetic analyses. We found a close genetic relationship between the Heze population and Nanyang, Hefei, Sanya, Fuyang and Wuhan populations. Besides, we surveyed the fruit's origin in the wholesale market, and concluded that B. dorsalis trapped in Heze might have come from Hainan and Zhejiang in China. Finally, overwintering potential experiments showed that a small number of pupae could survive during the test periods in Nanyang, whereas no pupae could survive in Heze. Overall, this study reveals that the Nanyang population of B. dorsalis were resident, whereas the Heze population did not colonize and were repeated entries from other areas every spring.