Comparative life history traits of indigenous Italian parasitoids of Drosophila suzukii and their effectiveness at different temperatures

Drosophila suzukii, or Spotted Wing Drosophila (SWD), is a highly polyphagous invasive pest which has recently invaded Europe and the Americas. Its huge economic impact is due in part to a lack of specialised natural enemies suppressing population outbreaks in newly invaded areas. By establishing new associations, endemic parasitoid species native to the invaded areas can play an important role in controlling the pest. This study aims to provide a range of baseline information on the developmental parameters and parasitisation efficacy of three Italian populations of D. suzukii parasitoids at different temperatures. The species tested were a larval parasitoid, Leptopilina heterotoma (Thomson), and two pupal parasitoids, Pachycrepoideus vindemiae (Rondani) and Trichopria drosophilae (Perkins). Two comparative experiments were set up: the first assessing longevity and the lifetime fecundity of each species at 23°C, and the second investigating the effect of temperature on parasitisation efficacy, developmental time and sex-ratio. The results revealed different fecundity patterns for the three parasitoids, probably due to a different level of synovigeny. For T. drosophilae and P. vindemiae, the lifetime sex ratio was biased towards an increasing number of males, whereas L. heterotoma showed the opposite trend. Moreover, temperature markedly affected host-parasitoid interaction and was positively correlated with the parasitoid's developmental time, whereas the sex-ratio was not significantly influenced. On the basis of these experiments, T. drosophilae appears to be the best candidate for developing a biological control strategy.