Potential life-history costs of parasitoid avoidance in Drosophila melanogaster

Pupal parasitoids are a common natural enemy of Drosophila. As Drosophila pupae do not have an immunological defence against pupal parasitoids, they have to avoid being attacked. As a first step to identifying the costs of avoidance of parasitism by pupal parasitoids, we explored three traits that potentially influence the probability of D. melanogaster pupae to survive attack by Pachycrepoideus vindemiae. We found that larvae pupating on the food source had a higher probability of avoiding parasitism, but that the distance that larvae pupate away from the food had no effect on survival probability when exposed to pupal parasitoids. We also found no indication that the thickness of the puparial wall influences risk of parasitism. Pupal size, however, was correlated with the probability of surviving parasitoid attack, with smaller pupae having a higher survival probability. If pupal size is indeed the key trait influencing risk of parasitism of D. melanogaster pupae by P. vindemiae, the potential life-history costs of parasitoid avoidance are smaller adult size, leading to lower general fitness.