Summary There are major impediments to finding improved DEET alternatives because the receptors causing olfactory repellency are unknown, and new chemistries require exorbitant costs to determine safety for human use. Here we identify DEET-sensitive neurons in a pit-like structure in the Drosophila antenna called the sacculus. They express a highly conserved receptor Ir40a and flies in which these neurons are silenced or Ir40a is knocked down lose avoidance to DEET. We use cheminformatics to screen >400,000 compounds and identify >100 natural compounds as candidate repellents. We test several and find that most activate Ir40a+ neurons and are repellents for Drosophila. These compounds are strong repellents in mosquitoes as well. The candidates contain chemicals that do not dissolve plastic, are affordable, smell mildly like grapes, with three being considered safe for human consumption. Our findings pave the way to discover new generations of repellents that will help fight deadly insect-borne diseases worldwide.

In both mammals and insects, an olfactory neuron will usually select a single olfactory receptor and repress remaining members of large receptor families. Here we show that a conserved multiprotein complex, Myb-MuvB (MMB)/dREAM, plays an important role in mediating neuron-specific expression of the carbon dioxide (CO 2 ) receptor genes (Gr63a/Gr21a) in Drosophila. Activity of Myb in the complex is required for expression of Gr63a/ Gr21a and acts in opposition to the histone methyltransferase Su(var)3-9. Consistent with this, we observed repressive dimethylated H3K9 modifications at the receptor gene loci, suggesting a mechanism for silencing receptor gene expression. Conversely, other complex members, Mip120 (Myb-interacting protein 120) and E2F2, are required for repression of Gr63a in inappropriate neurons. Misexpression in mutants is accompanied by an increase in the H3K4me3 mark of active chromatin at the receptor gene locus. Nuclei of CO 2 receptor-expressing neurons contain reduced levels of the repressive subunit Mip120 compared with surrounding neurons and increased levels of Myb, suggesting that activity of the complex can be regulated in a cell-specific manner. Our evidence suggests a model in which olfactory receptors are regulated epigenetically and the MMB/dREAM complex plays a critical role in specifying, maintaining, and modulating the receptor-to-neuron map.

Odorants activate receptors in the peripheral olfactory neurons, which sends information to higher brain centers where behavioral valence is determined. Movement and airflow continuously change what odor plumes an animal encounters and little is known about the effect one plume has on the detection of another. Using the simple Drosophila melanogaster larval model to study this relationship we identify an unexpected phenomenon: response to an attractant can be selectively blocked by previous exposure to some odorants that activates the same receptor. At a mechanistic level, we find that exposure to this type of odorant causes prolonged tonic responses from a receptor (Or42b), which can block subsequent detection of a strong activator of that same receptor. We identify naturally occurring odorants with prolonged tonic responses for other odorant receptors (Ors) as well, suggesting that termination-kinetics is a factor for olfactory coding mechanisms. This mechanism has implications for odor-coding in any system and for designing applications to modify odor-driven behaviors.

A fundamental molecular feature of olfactory systems is that individual neurons express only one receptor from a large odorant receptor gene family. While numerous theories have been proposed, the functional significance and evolutionary advantage of generating a sophisticated one-receptor-per neuron expression pattern is not well understood. Using the genetically tractable Drosophila melanogaster as a model, we demonstrate that the breakdown of this highly restricted expression pattern of an odorant receptor in neurons leads to a deficit in the ability to exploit new food sources. We show that animals with ectopic co-expression of odorant receptors also have a competitive disadvantage in a complex environment with limiting food sources. At the level of the olfactory system, we find changes in both the behavioral and electrophysiological responses to odorants that are detected by endogenous receptors when an olfactory receptor is broadly misexpressed in chemosensory neurons. Taken together these results indicate that restrictive expression patterns and segregation of odorant receptors to individual neuron classes are important for sensitive odor-detection and appropriate olfactory behaviors.

We are retracting this Article because we no longer have confidence in data that support one of our key conclusions. In this Article we reported four advances in insect repellency: identification of olfactory neurons in Drosophila melanogaster that participate in repellency to N,N-diethyl-meta-toluamide (DEET); identification of an ionotropic receptor, Ir40a, expressed in these neurons required for avoidance to DEET; development of a chemical informatics method of identifying shared structural features from known behavioural repellents; and validation of a series of computationally identified natural chemicals as repellents for flies and mosquitoes. We no longer have confidence in data supporting that Ir40a is a DEET receptor. Upon reanalysis, the original calcium imaging (GCAMP) data show movement artefacts and background effects that we originally missed, which seriously undermine our confidence in Ir40a responses to DEET. In addition, Supplementary Fig. 5b presents several inappropriately re-used panels.Upon learning that A. F. Silbering et al. 1 did not find defects in DEET aversion in Ir40a mutant flies, we repeated many of the original behaviour experiments. Although we confirmed significant behavioural differences in Ir40a cell-silenced flies (Ir40a-Gal4;UAS-TNTG), as reported in Fig. 2d, we have been unable to replicate observations of behavioural experiments using Ir40a-Gal4;UAS-RNAi flies. Therefore, with the exception of author Pinky Kain, we no longer have confidence in the conclusions of Figs 2, 3 and 5c, and Supplementary Fig. 5. We remain confident of the chemical informatics analyses and the identification of new repellents, which have been successfully repeated in our laboratory and by others, as reported in Figs 4, 5d and e, 6, and Supplementary Figs 2 and 6-9. Although it may still be possible that Ir40a does respond to DEET, given the issues listed above, all authors except Pinky Kain wish to retract this Article in its entirety. We deeply regret these circumstances and apologize to the scientific community.