Host-adaptation of parasitoids to the newly introduced invasive species, Drosophila suzukii

The reciprocal evolutionary interaction between a pest and its natural enemies leads to a dynamic runaway escalation or ‘arm-race’. The final result of this co-evolutionary process between species guarantees the population control, leading to an ecological balance. This balance is no longer maintained when a pest colonizes a new environment, in which specific biological control agents are lacking. The present study focused to determine the field occurrence of indigenous parasitoids of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). Since its introduction in USA and Europe in 2008, this invasive pest caused hundred thousand dollars worth of damage to small and stone fruits business. The uncontrolled outbreaks of D. suzukii in the invaded regions were mainly due to the absence of specialized natural enemies. On the contrary, in the areas of D. suzukii origin, a number of hymenopteran parasitoids, having a co-evolutionary history with this pe st, have been reported. Here we state the results of a survey aimed at determining the presence of indigenous D. suzukii parasitoid populations carried out from May to October 2012 in two areas negatively affected by this fruit pest: Trento Province, Northern Italy., and Oregon in the Pacific Northwest of the USA. We conducted field and laboratory studies in order to determine the status of biological control agents utilizing D. suzukii as a host. Our study sites included a range of commercial soft fruit and natural non-commercial habitats. In each site, sentinel traps were baited with either D. suzukii or Drosophila melanogaster Meigen (Diptera: Drosophilidae) larvae in different food substrates. The generalist parasitoid, Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae), was collected from both D. suzukii and D. melanogaster pupae in traps deployed in a selection of these sites. This report of P. vindemiae in 2012 represents the first identification of D. suzukii parasitoids in Europe. A successive parasitism efficacy test was set up under controlled conditions confirming the ability of P. vindemiae to attack D. suzukii pupae. We discuss the possible practical implications of this finding for the biological control of D. suzukii