Ionotropic Receptor IR75q.2 Mediates Avoidance Reaction to Nonanoic Acid in the Fall Armyworm (Lepidoptera, Noctuidae).

Ionotropic receptors (IRs) play an important role in olfaction, but little is known in nondrosophila insects. Here, we report and functional characterization of IR75q.2 in the invasive moth pest . First, 13 IRs (including four coreceptor IRs) were found specifically or highly expressed in adult antennae. Second, these IRs were tested for responding profiles to 59 odorants using the oocyte expression system, showing that only SfruIR75q.2 responded to 8-10C fatty acids and their corresponding aldehydes, with SfruIR8a as the only coreceptor. Third, the three acids (especially nonanoic acid) showed repellent effects on moth's behavior and oviposition, but the repellence significantly reduced to the insects with IR75q.2 knockout by CRISPR/Cas9. Taken together, our study reveals the function of SfruIR75q.2 in perception of acid and aldehyde odorants and provides the first evidence for olfactory function of an odor-specific IR in Lepidoptera.