Effects of plant-mediated differences in host quality on the development of two related endoparasitoids with different host-utilization strategies.

Among parasitoids that develop inside the bodies of feeding, growing hosts (so-called 'koinobiont' endoparasitoids), two strategies have evolved to dispose of host resources. The larvae of one group consumes most host tissues before pupation, whereas in the other the parasitoid larvae consume only host hemolymph and fat body and at maturity emerge through the host cuticle to pupate externally. Here we compared development and survival (to adult emergence) of two related larval endoparasitoids (Braconidae: Microgastrinae) of the diamondback moth, Plutella xylostella. Larvae of Dolichogenidea sicaria are tissue feeders whereas larvae of Cotesia vestalis are hemolymph feeders. Here, development of P. xylostella and the two parasitoids was compared on three populations (one cultivar [Cyrus], two wild, [Winspit and Kimmeridge]) of cabbage that have been shown to vary in direct defense and hence quality. Survival of P. xylostella and C. vestalis (to adult eclosion) did not vary with cabbage population, but did so in D. sicaria, where survival was lower when reared on the wild populations than on the cultivar. Furthermore, adult herbivore mass was significantly higher and development was significantly shorter in moths reared on the cultivar. The tissue-feeing D. sicaria was larger but took longer to develop than the hemolymph-feeder C. vestalis. The performance of both parasitoids was better on the cabbage cultivar than on the wild populations, although the effects were less apparent than in the host. Our results show that (1) differences in plant quality are diffused up the food chain, and (2) the effects of host quality are reflected on the development of both parasitoids.