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. 2010 Aug 26;67(4):555-61.
doi: 10.1016/j.neuron.201007006.

Avoiding DEET through insect gustatory receptors

Affiliations

Avoiding DEET through insect gustatory receptors

Youngseok Lee et al. Neuron. .

Abstract

DEET is the most widely used insect repellent worldwide. In Drosophila olfactory receptor neurons (ORNs), DEET is detected through a mechanism employing the olfactory receptor, OR83b. However, it is controversial as to whether ORNs respond directly to DEET or whether DEET blocks the response to attractive odors. Here, we showed that DEET suppressed feeding behavior in Drosophila, and this effect was mediated by gustatory receptor neurons (GRNs). DEET was potent in suppressing feeding as <0.1% DEET elicited aversive behavior. Inhibition of feeding required multiple gustatory receptors (GRs) expressed in inhibitory GRNs. DEET stimulated action potentials in GRNs that respond to aversive compounds, and this response was lost in the Gr32a, Gr33a, and Gr66a mutants. Since 0.02% DEET elicited action potentials, we conclude that DEET directly activates of GRNs. We suggest that the effectiveness of DEET in pest control owes to its dual action in inducing avoidance simultaneously via GRNs and ORNs.

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Figures

Figure 1
Figure 1. Behavioral avoidance to DEET is mediated by gustatory receptor neurons
(A) Structure of DEET (B–D) Binary food choice assays using Drosophila melanogaster. All assays were performed with 5 mM sucrose (either alone or mixture with each indicated concentration of DEET) and 1 mM sucrose. The dotted lines indicate a lack of bias between the two alternative food choices (P.I.=0.5). The experiments presented were conducted in a blind manner. (B) Dose response curve using the wild-type control flies (w1118) and the indicated concentrations of DEET. (C) Binary assays performed after the ORNs or GRNs were either ablated or inactivated. The cell death gene (UAS-hid) or the Kir2.1 channel (UAS-Kir2.1) were expressed in ORNs or GRNs under control of the Gr33a-GAL4 (Gr33aGAL4/+) or the Or83b-GAL4. The normal DEET avoidance in Or83b-GAL4/UAS-Kir2.1 flies was not due to ineffectiveness of these transgenes to effect olfaction since these flies did not avoid 0.1% benzaldehyde (Figure S1B). (D) Transient synaptic ablation of aversive GRNs using the Gr33a-GAL4 (Moon et al., 2009) and UAS-shits1. The assays were performed at the permissive (30°C) and non-permissive temperatures for the shits1. (E) Schematic illustration of gustatory sensilla on the fly labellum. We used the short sensillum (s6) for most tip recordings. (F) Dose response curve using DEET and s6 sensilla. The error bars indicate S.E.M.s. (G) Representative tip recordings obtained from an s6 sensillum and a long (l4) sensillum using buffer only, 0.2% DEET or 50 mM sucrose. The asterisks indicate the addition of the recording pipets to the sensilla. Arrowheads indicate tastant-induced action potentials.
Figure 2
Figure 2. Three gustatory receptors are required for DEET avoidance using the binary food choice assay
(A) Survey of Gr mutants and the Or83b2 mutant for defects in the aversion to 0.2% DEET. Gr66aex represents Gr66aex83. (B–D) Rescue of the avoidance defects in response to 0.1% and 0.2% DEET using wild-type Gr transgenes. Most data were collected in a blind manner. However, similar results were obtained when the data were collected in non-blinded experiments (e.g. Figures S2A and S2B). (B) Two Gr33a alleles, Gr33a1 and Gr33aGAL4, displayed similar impairments in aversion to DEET. The behavior was rescued by expression of UAS-Gr33a+ under control of the Gr33aGAL4. See Figure S2A and S2B for additional information. (C) The deficit in ΔGr32a was rescued with a Gr32a+ genomic fragment, gGr32a+. See Figure S2D for additional rescue data using the GAL4/UAS system. (D) Rescue of the Gr66aex83 DEET avoidance defect. The genomic DNA included in the 8-Gr66a+ transgene encoded Gr66a+ and two flanking genes (CG7066 and CG7188) (Moon et al., 2006). The genomic DNA in 7-Gr66a− included the two flanking genes, but not Gr66a. The error bars indicated S.E.M.s.
Figure 3
Figure 3. DEET-induced action potentials required Gr66a, Gr33a and Gr32a
(A) Tip recordings showing the mean responses in s6 sensilla to 0.2% DEET. The deficits in the Gr66aex83, Gr33a1 and ΔGr32a mutants were rescued significantly by the wild-type transgenes. The rescue control for Gr66a was 7-Gr66a− and the rescue transgene was 8-Gr66a+. Gr66aex stands for Gr66aex83. The Gr33a rescue construct was UAS-Gr33a+ and the Gr32a rescue was performed using the genomic transgene, gGr32a+. The error bars indicate S.E.M.s. (B) Representative traces of DEET-induced action potentials in the wild-type control, Gr33a1 and Gr33a expressing the wild-type transgene: Gr33a1/Gr33aGAL4;UAS-Gr33a/+. The times when the recording pipets were applied to the s6 sensilla are indicated by the asterisks. Arrowheads indicate DEET-induced action potentials.
Figure 4
Figure 4. Durability and toxicity of DEET and requirements for Gr32a and Gr66a for the responses to multiple naturally occurring repellent compounds
(A) and (C) Tip recordings. (B) and (D) Two-way choice tests. (A) ΔGr32a flies showed reduced frequencies of action potentials in response to several repellent compounds (also refer to Figure S3A), but a normal caffeine response. (B) ΔGr32a flies were impaired in behavioral avoidance to multiple repellent compounds (also refer to Figure S3B). (C) The frequencies of action potentials induced by lobeline, papaverine and strychnine were nearly eliminated in Gr66aex83. These defects were rescued significantly by 8-Gr66a+, but not by 7-Gr66a−. (D) The behavioral avoidances to lobeline and papaverine were reduced in Gr66aex83. These defects were reversed by 8-Gr66a+, but not by 7-Gr66a−. The slight reduction in the behavioral avoidance to strychnine was statistically significant. (E) Time-dependent effects on the survival of wild-type control flies resulting from consuming 1% sucrose combined with the indicated concentrations of DEET. The error bars indicated S.E.M.s.

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