BACKGROUNDHow parasitoids distinguish hosts from non‐hosts remains an unknown question. Chouioia cunea Yang (Eulophidae) is an important fall webworm parasitoid that attacks many forest and agricultural pests. To study the differences in the chemical clues used by C. cunea to distinguish host and non‐host plants, we used gas chromatography–mass spectrometry (GC–MS) to identify volatile compounds of two C. cunea hosts (Hyphantria cunea and Helicoverpa armigera) and two non‐hosts (Spodoptera exigua and Spodoptera frugiperda). Additionally, we used behavioral assays to compare the attraction of C. cunea to various compounds.RESULTSThe two natural host species were more attractive than the two non‐host species, in the following order: Hyphantria cunea > Helicoverpa armigera > S. exigua = S. frugiperda. The pupae of the natural hosts contained 1‐dodecene, which was not produced by the two natural non‐hosts. When the ‘attractants’ based on the difference between the species‐specific blend emitted by pupae and the optimal blend were sprayed onto the natural non‐host pupae, they significantly improved the attraction of C. cunea to the non‐host pupae.CONCLUSIONThese results revealed that specific host‐produced volatile compounds guide C. cunea to distinguish between natural hosts and non‐hosts. Overall, this study provides a foundation for developing a behavior‐modifying strategy to re‐direct C. cunea attacks to control important non‐host pests. © 2023 Society of Chemical Industry.

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Based on the “enemy-free space” hypothesis, in order to avoid natural enemies, insects may prefer host plants that are nutritionally suboptimal but are less visited by their natural enemies. The fall webworm, Hyphantria cunea Drury has more than 600 reported hosts. Chouioia cunea, a parasitoid wasp, is the main natural enemy of H. cunea. We addressed the question whether the preference of H. cunea for host plants correlate with attractiveness of the plants to C. cunea. H. cunea larvae were reared on leaves of eight different host plants, and the relationship between H. cunea host preference and preferences of the parasitic wasp were evaluated. The preferred host plant of female H. cunea was mulberry, Morus alba. Compared with other plants, M. alba was a poor nutritional host for H. cunea. However, compared with other host plants, M. alba attracted fewer natural enemies C. cunea. GC-MS combined with GC-EAD analysis revealed six compounds in the volatiles of different plant HIPVS after feeding by H. cunea. Behavioral assays showed that tridecane alone did not elicit any attraction or repellency responses of the host H. cunea or the parasitoid C. cunea. When tridecane was mixed with other HIPVS, however, the mixture could attracted C. cunea and repelled H. cunea. Notably, only M. alba HIPVS did not contain tridecane. Thus, H. cunea exploits M. alba as an enemy-free space, minimizing attacks by the parasitoid C. cunea. This information underscores that adaptive responses of herbivores need to be considered in the context of multi-trophic relationships rather than optimizing herbivore growth on the most nutritionally adaptive plant host.