Insect repellents that discourage feeding on crops are known as antifeedants. A commonly used insect repellent is DEET (N,N-dimethyl-m-toluamide). DEET is volatile and can be detected by the olfactory receptor OR83b, which is present in olfactory receptor neurons (ORNs). However, it was not clear whether DEET can also be detected through the sense of taste and whether it can act as an antifeedant. Lee et al. found that Drosophila avoided a sucrose solution to which low concentrations of DEET had been added, thus indicating that DEET was an antifeedant. Ablation of gustatory receptor neurons (GRNs), rather than ORNs, or blocking synaptic activity in GRNs decreased aversion to DEET-laced sucrose solution. Action potentials were observed upon application of DEET in the bristles of various s-type taste sensilla that respond to aversive compounds, thus indicating that DEET directly activated GRNs. DEET-induced repulsion and action potentials in sensilla required the gustatory receptors Gr66a, Gr63a, and Gr32a. Thus, DEET acts as an antifeedant by activating gustatory receptors involved in mediating aversive responses.
Y. Lee, S. H. Kim, C. Montell, Avoiding DEET through insect gustatory receptors. Neuron 67, 555–561 (2010). [PubMed]