| The guava fruit fly, Bactrocera (Bactrocera) correcta (Bezzi)(Diptera:Tephritidae) is one of the most important pests of many kinds of tropical and subtropical fruits and vegetables, such as guavas, citruses mangoes and chili peppers. It is mainly distributed in Asia. With the growth of international trade and human activities, this fly can easily follow the transport of its host plants and perform a long-distance dispersal, posed a threat to agricultural production of importing countries. With the aim of investigating population genetic structure, invasion routes and expansion trend of B. correcta in the main distribution areas, and to reveal the sources of invasion of this fly in Yunnan province of China, We have analysed the combinative data of mitochondrial COI sequences and microsatellite markers, and got the following conclusions:1) We used mtDNA COI sequences as genetic markers to analyse population genetic structure of793B. correcta individuals colleted from20sites in7countries, including China (Yunnan), Thailand, Laos, Myanmar, Vietnam, Sri lanka and India. Our study suggests that the overall genetic structure of this fly in main distribution areas was significant. There has no sign of Isolation-by-distance. Haplotype diversity decreased with the increasing of longitude of collection sites, it showed that this fly has expanded from west to east with a limited geographical scale. Two main invasion routes of B. correcta are inferred:(1) As the results of monsoon in Bengal, this fly performed eastward dispersal from South Asia to Western Yunnan of China, then established its population in that area and gradually spread to Mandalay of Myanmar, that formed the spread route as South Asiaâ†'Western Yunnanâ†'Mandalay (Myanmar);(2) As the results of natural dispersal or human activities, this fly performed northward dispersal from Central Thailand and Laos regions to Southern Yunnan, Northern Thailand and Laos regions, and then introduced into Yunnan province through Jinghong region in Southern Yunnan. Finally, this fly gradually northward expansed to Central Yunnan and eastward expansed to Eastern Yunnan and Vietnam, respectively. That formed the spread route as Central Thailand and Laosâ†'Northern Thailand, Northern Laos and Southern Yunnanâ†'Central Yunnanâ†'Eastern Yunnan and Vietnam.2) We firstly used a biotin-streptavidin capture method to isolate12microsatellite markers of B. correcta from a (AC)15microsatellite library. The enrichment efficiency was52.31%. The polymorphism of these microsatellite loci was tested in74individuals collected from two natural populations using TP-M13-SSR technique. Based on our research,117allele were found in all12loci, the number of allele per locus varied from6-14, the polymorphic information contents ranged from0.41-0.79.10loci were conformed to HWE. No significant departures from linkage disequilibrium were found between each pairs of loci. These12microsatellite markers demonstrated high levels of polymorphism. It can be used as reliable markers for the studies of population genetic structure in this fly. 3) We used all above microsatellite loci to analyse population genetic structure of781B. corrceta individuals collected from above18sites in5countries (except for Sri Lanka and India). Our study suggests that the overall genetic structure of this fly in18sites was significant. There has no sign of Isolation-by-distance. The migration rates between all18populations were generally high. Based on our study, B. correcta might be invaded into Yunnan province through Mangshi in Western Yunnan and Jinghong in Southern Yunnan. B. correcta populations in Eastern Yunnan and Vietnam region occurred lately, the populations in Central Yunnan might be the sources of invasion in this region. |
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