An insect chemosensory protein facilitates locust avoidance to fungal pathogens via recognition of fungal volatiles

Abstract

Locusts (Locusta migratoria) are one of the most destructive insect pests worldwide. Entomopathogenic fungi can infect and kill locusts, with Metarhizium acridum having evolved as a specialized acridid pathogen. However, locusts have evolved countermeasures to limit or avoid microbial pathogens, although the underlying molecular mechanisms behind these defenses remain obscure. Here, we demonstrate that L. migratoria exhibit avoidance behaviors towards M. acridum contaminated food via recognition of fungal volatiles, with locust perception of the volatile mediated by the LmigCSP60 chemosensory protein. RNAi-knockdown of LmigCSP60 lowered locust M. acridum avoidance behavior and increased infection and mortality. The fungal volatile, 2-phenylethanol (PEA), was identified to participate in locust behavioral avoidance. RNAi-knockdown of LmigCSP60 reduced antennal electrophysiological responses to PEA and impaired locust avoidance to the compound. Purified LmigCSP60 was able to bind a set of fungal volatiles including PEA. Furthermore, reduction of PEA emission by M. acridum via construction of a targeted gene knockout mutant of the alcohol dehydrogenase gene (ΔMaAdh strain) that contributes to PEA production reduced locust avoidance behavior towards the pathogen. These findings identify an olfactory circuit used by locusts to detect and avoid potential microbial pathogens before they are capable of initiating infection and highlight behavioral and olfactory adaptations affecting the co-evolution of host-pathogen interactions.