Selection results of two native parasitoids on the invasive spotted wing drosophila

Co-evolved natural enemies provide sustainable and long-term control of
numerous invasive insect pests, but the introduction of such enemies has
declined sharply due to increasing regulations. In the absence of
co-evolved natural enemies, native species may attack exotic invasive
pests; however, they usually lack adaptations to control 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 D. melanogaster
serving as the co-evolved host. We assessed the 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 by significantly increasing their
developmental success on the novel host within three generations, which
remained constant for seven additional generations without 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 ten 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 suggest
that a few generations of selection may be sufficient to improve the
performance of native parasitoids on invasive hosts, but with limits to
the degree of improvement for managing invasive pests when exotic
co-evolved natural enemies are unavailable.