Fitness consequences of body-size-dependent parasitism in a gregarious parasitoid attacking the 7-spot ladybird, Coccinella septempunctata (Coleoptera: Coccinellidae)

Abstract

Variation in body size of hosts and their parasitoids poses a significant challenge for gregarious parasitoid females to make their decisions to optimally utilize a range of hosts. In the present study, we investigated the combined effect of host size across successive host larval stages and maternal wasp size on fitness-correlated performances of offspring parasitoids, using the larval-pupal gregarious parasitoid Oomyzus scaposus attacking the 7-spot ladybird Coccinella septempunctata. The probability of parasitism success decreased with ladybird body weight at the time of parasitism when small sized wasps made the attack, but maintained a high level across the full range of host weights when large sized wasps made it. Offspring development time to adulthood decreased, while brood size increased, asymptotically with host body weight, but they did not vary with maternal wasp size. Sex ratio was female-biased and did not vary with ladybird body weight or maternal wasp size. Body size of F1 adult parasitoids did not vary with ladybird body weight or maternal wasp size. Our findings suggest that small 7-spot ladybird larvae are preferred hosts for small O. scaposus females, while large sized ladybird larvae appeared to have little or no effect on parasitism success of large female parasitoids.