Repellent compound with larger protective zone than DEET identified through activity-screening of Ir40a neurons, does not require Or function

Abstract

The widely used insect repellent DEET has a limited spatial zone of protection, requiring it to be applied over all exposed areas of skin. Identification of insect DEET-sensing neurons expressing a highly conserved Ionotropic receptor, Ir40a, provides an opportunity to identify new structural classes of volatile agonists as potential spatial repellents. By imaging the activity of the Ir40a+ neurons in D. melanogaster expressing the calcium sensitive GCaMP3 protein, we identify a strong agonist, 4-methylpiperidine, with a much higher vapor pressure than DEET. Behavioral testing reveals that 4-methylpiperidine repels Aedes aegypti, which is consistent with our model that Ir40a marks a conserved innate aversive pathway. Using a spatial repellency assay we demonstrate that 4-methylpiperidine applied to one part of the hand repels mosquitoes on another part effectively, whereas DEET cannot do so. Using orco mutant A. aegypti we demonstrate that avoidance to 4- methypiperidine is not dependent on Or family function. Additional testing of orco mutant mosquitoes demonstrates that they are also effectively repelled by DEET, without coming in contact with it, in heat attraction assays. Together, these results support our initial observations that the conserved Ir pathway plays a key role in olfactory repellency and can be used to identify new classes of repellents.