Competitive superiority switches between larval and adult stages reducing the fitness difference between competing parasitoids.

Shifts in resource use in response to interspecific competition were thought to be necessary for the stable coexistence of consumers sharing the same resources. However, if superiority between competitors switches during development, they may achieve similar lifetime fitness without changing resource use. We tested this hypothesis by allowing two parasitoid wasp species, Pachycrepoideus vindemiae Rondani (Hymenoptera: Pteromalidae) and Trichopria drosophilae Perkins (Hymenoptera: Diapriidae), to exploit large and small Drosophila melanogaster Meigen (Diptera: Drosophilidae) pupae separately or simultaneously to examine whether they change their host preferences in response to interspecific competition. The results showed that both parasitoid species preferred large over small hosts regardless of the presence of competitors, although immature T. drosophilae generally shows a higher mortality rate than P. vindemiae when they shared the same host pupae. This could be explained by the higher fitness loss of T. drosophilae in small hosts, as body size, longevity, and fecundity of T. drosophilae offspring suffered more from a decrease in host size than P. vindemiae. In contrast, adult female T. drosophilae laid more eggs than P. vindemiae, which enabled them to outperform P. vindemiae during host exploration. Consequently, the two parasitoid species had similar numbers of offspring when they were allowed to exploit the host pupae simultaneously. This study provides insights into our understanding of how competing parasitoid species may coexist on the same resources. [ABSTRACT FROM AUTHOR]