Invasive insect pests are most effectively controlled in the long term by co-evolved natural enemies that may be introduced as part of classical biological control programs. However, the introduction of such enemies has declined sharply due to increasing regulations. Native natural enemies, such as insect parasitoids may attack exotic invasive pests; however, they usually lack adaptations to control these novel hosts effectively. We investigated the potential of two native pupal parasitoids, Pachycrepoideus vindemmiae and Trichopria drosophilae, to increase their developmental success on the invasive Drosophila suzukii. Replicated populations of the two parasitoids were subjected to 10 generations of laboratory selection on D. suzukii with Drosophila melanogaster serving as the co-evolved host. We assessed developmental success of selected and control lines in generations 0, 3, and 10. Changes in host preference, sex ratio, development time, and body size were measured to evaluate correlated responses with adaptation. Both parasitoid species responded rapidly to selection, increasing their developmental success by 259% and 88% on the novel host within three generations. Seven additional generations of selection did not result in further improvement. The generalist parasitoid species P. vindemmiae was able to reach similar developmental success as the control populations, while the performance of the more specialized parasitoid T. drosophilae remained lower on the novel than on the co-evolved host. There was no increase in preference towards the novel host over 10 generations of selection nor were there changes in development time or body size associated with adaptation in either parasitoid species. The sex ratio became less female-biased for both parasitoids after three generations of selection but rebounded in P. vindemmiae by generation 10. These results demonstrate that rapid evolution of increased virulence is possible even from low genetic diversity, with implications for integrating evolutionary techniques into biological control of invasive species.
