The relative fitness of Drosophila melanogaster (Diptera, Drosophilidae) that have successfully defended themselves against the parasitoid Asobara tabida (Hymenoptera, Braconidae)

Drosophila melanogaster larvae defend themselves against parasitoid attack via the process of encapsulation. However, flies that successfully defend t hem selves have reduced fitness as adults. Adults which carry an encapsulat ed parasitoid egg are smaller and females produce significantly fewer eggs than controls. Capsule-bearing males allowed repeated copulations with fema les do not show a reduction in their number of offspring, but those allowed to copulate only once did. No differences were found in time to first ovip osition in females, or in time to first copulation in males. We interpret t he results as arising from a trade-off between investing resources in facto rs promoting fecundity and mating success, and in defence against parasitis m. The outcome of this investment decision influences the strength of selec tion for defence against parasitism.