Odorant inhibition in mosquito olfaction mediated by inverse agonists

The Odorant Receptor Recognizing Camphor in a Camphor Tree Specialist Orthaga achatina (Lepidoptera: Pyralidae)

Camphor has been used as an effective repellent and pesticide to stored products for a long history, but Orthaga achatina (Lepidoptera: Pyralidae) has evolved to specifically feed on the camphor tree Cinnamomum camphora. However, the behavioral response of O. achatina to camphor and the molecular basis of camphor perception are totally unknown. Here, we demonstrated that both male and female adults were behaviorally attracted to camphor, suggesting the adaptation of O. achatina to and utilization of camphor as a signal of C. camphora. Second, in 40 O. achatina OR genes obtained by analyzing antenna transcriptomes, only OachOR16/Orco significantly responded to camphor in the Xenopus oocyte system. Finally, by molecular docking analysis and site-directed mutagenesis, the Ser209 residue is confirmed to be essential for binding of the oachOR16 with camphor. This study not only reveals the camphor-based host plant choice and olfactory mechanisms of O. achatina but also provides a molecular target for screening more potential insect repellents.

A mosaic of endogenous and plant-derived courtship signals in moths

Insects rely on olfaction to guide a wide range of adaptive behaviors, including mate and food localization, mate choice, oviposition site selection, kin recognition, and predator avoidance.1 In nocturnal insects, such as moths2 and cockroaches,3 mate finding is stimulated predominantly by long-range species-specific sex pheromones, typically emitted by females. During courtship, at close range, males in most moth species emit a blend of pheromone compounds from an everted, often large, pheromone gland. While long-distance communication with sex pheromones has been remarkably well characterized in thousands of moth species,2,4 close-range chemosensory sexual communication remains poorly understood. We reveal that in the moth Chloridea virescens, the male pheromone consists of three distinct classes of compounds: de novo biosynthesized alcohols, aldehydes, acetates, and carboxylic acids that resemble the female's emissions; newly identified compounds that are unique to the male pheromone, such as aliphatic polyunsaturated hydrocarbons; and sequestered plant secondary compounds and hormone derivatives, including methyl salicylate (MeSA). Thus, males employ a mosaic pheromone blend of disparate origins that may serve multiple functions during courtship. We show that two olfactory receptors in female antennae are tuned to MeSA, which facilitates female acceptance of the male. Because MeSA is emitted by plants attacked by pathogens and herbivores,5 the chemosensory system of female moths was likely already tuned to this plant volatile, and males appear to exploit the female's preadapted sensory bias. Interestingly, while female moths (largely nocturnal) and butterflies (diurnal) diverged in their use of sensory modalities in sexual communication,6 MeSA is used by males of both lineages.