Gustatory Receptors Required for Avoiding the Insecticide l-Canavanine

Insect survival depends on contact chemosensation to sense and avoid consuming plant-derived insecticides, such as l-canavanine. Members of a family of ∼60 gustatory receptors (GRs) comprise the main peripheral receptors responsible for taste sensation in Drosophila . However, the roles of most Drosophila GRs are unknown. In addition to GRs, a G protein-coupled receptor, DmXR, has been reported to be required for detecting l-canavanine. Here, we showed that GRs are essential for responding to l-canavanine and that flies missing DmXR displayed normal l-canavanine avoidance and l-canavanine-evoked action potentials. Mutations disrupting either Gr8a or Gr66a resulted in an inability to detect l-canavanine. We found that l-canavanine stimulated action potentials in S-type sensilla, which were where Gr8a and Gr66a were both expressed, but not in Gr66a -expressing sensilla that did not express Gr8a . l-canavanine-induced action potentials were also abolished in the Gr8a and Gr66a mutant animals. Gr8a was narrowly required for responding to l-canavanine, in contrast to Gr66a , which was broadly required for responding to other noxious tastants. Our data suggest that GR8a and GR66a are subunits of an l-canavanine receptor and that GR8a contributes to the specificity for l-canavanine.