Fall Webworm Host Plant Preferences Generate a Reduced Predation Enemy-Free Space in Its Interaction with Parasitoids

Simple SummaryThe tri-trophic interactions among the fall webworm (Hyphantria cunea), its host plants, and its parasitoid wasp (Chouioia cunea) were investigated, with particular focus on the correlation betweenH. cunea’s host plant preference and the attractiveness of these plants toC. cunea. It was found thatMorus alba, despite providing suboptimal nutritional quality forH. cunealarvae, became the most preferred host plant due to its significantly reduced attraction toC. cuneacompared to alternative host species. Through volatile analysis,M. albawas identified to lack tridecane emission, a key semiochemical that attractsC. cunea. These results demonstrate adaptive host selection behavior inH. cuneathat minimizes parasitism risk, providing novel insights for refining biological control strategies against this invasive species.Plants and insects are developing strategies to avoid each other’s defense systems. Host plants may release volatile compounds to attract the natural enemies of herbivores; insect pests may also select host plants that are deterrent to natural enemies to avoid such predation. Here we investigated whether the host plant preference ofHyphantria cuneacorrelates with the attractiveness of these plants toChouioia cunea, a parasitoid wasp that serves as the primary natural enemy ofH. cunea. We foundMorus albawas the preferred host plant for femaleH. cunea. AlthoughM. albaprovided suboptimal nutritional value forH. cuneagrowth and development compared to other plants, it attracted fewerC. cunearelative to alternative host plants. Gas chromatography–mass spectrometry (GC–MS) coupled with gas chromatography–electroantennographic detection (GC-EAD) analysis identified six distinct compounds among the herbivore-induced plant volatiles (HIPVs) produced followingH. cuneafeeding. Notably,M. albawas the sole plant species that did not emit tridecane. These results suggest thatH. cuneautilizesM. albaas a reduced predation enemy-free space, thereby minimizing parasitization byC. cunea. Our research emphasizes the importance of considering adaptive responses of herbivores within the context of multi-trophic relationships, rather than solely focusing on optimizing herbivore growth on the most nutritionally suitable plant host.