Consequences of constitutive and induced variation in the host's food plant quality for parasitoid larval development

Constitutive and induced changes in plant quality impact higher trophic levels, such as the development 27 of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to 28 examine how the parasitoid larva is integrated within the host during the growth process. In two exper- 29 iments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval 30 development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval 31 growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host 32 was feeding on Brussels sprout plants that were either undamaged or were previously induced by cater- 33 pillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the special- 34 ist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting 35 differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was 36 also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Par- 37 asitoid growth wasmore depressed on induced than on undamaged control plants, andmore on wild cab- 38 bage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of 39 induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feed- 40 ing began inducing the previously undamaged control plants, the effect of induction disappeared, reveal- 41 ing a temporal component of plant–parasitoid interactions. This study demonstrates how insights into 42 the physiological aspects of host–parasitoid interactions can improve our understanding of the effects 43 of plant-related traits on parasitoid wasps.