Abstract:
Phytophagous insects of the genus Bactrocera are among the most economically
important invasive fruit fly pests. In 2003, an unknown Bactrocera species was found
in Kenya. First identified as an ‘aberrant form’ of the Asian B. dorsalis complex, it was
later recognized as a new species, Bactrocera invadens. Within 2 years of its discovery,
the species was recorded in several African countries, becoming an important
quarantine pest. As this invasive fly was discovered only recently, no data are
available on its invasion pattern in Africa. This pilot study attempts to infer from
genetic data the dynamic aspects of the African invasion of this pest. Using
microsatellite markers, we evaluated the level of genetic diversity and the extent of
common ancestry among several African populations collected across the invaded areas.
A sample from the Asian Sri Lankan population was analysed to confirm the Asian
origin of this pest. Genetic data cast no doubt that Sri Lanka belongs to the native
range, but only a small percentage of its genotypes can be found in Africa. African
populations display relatively high levels of genetic diversity associated with limited
geographical structure and no genetic footprints of bottlenecks. These features are
indicative of processes of rapid population growth and expansion with possible
multiple introductions. In the span of relatively few years, the African invasion
registered the presence of at least two uncorrelated outbreaks, both starting from the
East. The results of the analyses support that invasion started in East Africa, where
B. invadens was initially isolated.
