The oriental fruitfly Bactrocera dorsalis s.s. in East Asia: disentangling the different forces promoting the invasion and shaping the genetic make-up of populations.

The Oriental fruit fly, Bactrocera dorsalis sensu stricto, is one of the most economically destructive pests of fruits and vegetables especially in East Asia. Based on its phytophagous life style, this species dispersed with the diffusion and implementation of agriculture, while globalization allowed it to establish adventive populations in different tropical and subtropical areas of the world. We used nine SSR loci over twelve samples collected across East Asia, i.e. an area that, in relatively few years, has become a theatre of intensive agriculture and a lively fruit trade. Our aim is to disentangle the different forces that have affected the invasion pattern and shaped the genetic make-up of populations of this fruit fly. Our data suggest that the considered samples probably represent well established populations in terms of genetic variability and population structuring. The human influence on the genetic shape of populations and diffusion is evident, but factors such as breeding/habitat size and life history traits of the species may have determined the post introduction phases and expansion. In East Asia the origin of diffusion can most probably be allocated in the oriental coastal provinces of China, from where this fruit fly spread into Southeast Asia. The spread of this species deserves attention for the development and implementation of risk assessment and control measures.

Inferences on the population structure and colonization process of the invasive oriental fruit fly, 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.