Changes in arthropod community but not plant quality benefit a specialist herbivore on plants under reduced water availability

Plants growing under reduced water availability can affect insect herbivores differently, in some instances benefitting them. However, the forces mediating these positive impacts remain mostly unclear. To identify how water availability impacts plant quality and multitrophic interactions, we conducted manipulative field studies with two populations of the specialist herbivore Pieris rapae, and its host plant, Rorippa indica. We found that P. rapae larvae experienced higher survival on R. indica growing under low water availability compared with plants grown under high water availability. Higher survival of eggs and larvae was related to the reduced abundance of other herbivores and natural enemies. Water availability had differential impacts on other members of the herbivore community by altering plant quality. Low water availability decreased the quality of R. indica to most herbivores, as indicated by reduced abundance in the field and decreased relative growth rate in laboratory feed...