Parasitoids as taxonomists: how does the parasitoid Chouioia cunea distinguish between a host and a non-host?

How 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.

The 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.

These 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.