Uncovering the tracks of a recent and rapid invasion: the case of the fruit fly pest Bactrocera invadens (Diptera: Tephritidae) in Africa

Psyttalia concolor (Szepligeti) (Hymenoptera: Braconidae) is a parasitic wasp reared and released for the biological control of the olive fruit fly Bactrocera oleae (Gmelin) (Diptera: Tephritidae). We used RAPD (Random Amplified Polymorphic DNA) markers to assess the level of genetic differentiation in and between 11 introduced (‘‘wild”) Mediterranean populations (nine from South Italy, and two from the Middle East). The wasp populations from these areas differ for colonization history in terms of original released strain and time of release. We have also considered four mass-reared strains, three derived from Mediterranean wasps and one (Guatemala) from African specimens, in order to infer the degree of their genetic relationships with the considered ‘‘wild” Mediterranean samples. The similarity estimates indicate a high level of genetic homogeneity not only within the four mass-reared strains but also within the Italian and Middle East samples. Phenotypic AMOVA and cluster analyses highlight differentiation between the Italian samples and the Middle East samples. As expected, the three Mediterranean mass-reared strains show an intermediate position among the Mediterranean ‘‘wild” samples, while a major differentiation characterizes the Guatemala strain. Based on RAPD markers, SCAR (Sequence Characterized Amplified Regions) primers were developed. In the long term, these SCAR markers may offer a powerful tool to monitor the performance of biological control programmes.