Odorant receptor Or117 detects camphor to induce floral seeking by the mosquito Aedes aegypti.

Female mosquitoes display distinct, staged, and dynamic resource-seeking behaviors to sustain energy and reproductive demands. Teneral females are attracted to floral odors due to innate energy requirements. During maturation, females develop the competence to take a blood meal, a process expedited following mating and linked to a shift to vertebrate host cue attraction. The change in resource-seeking behaviors is correlated with an overall increase in abundance of chemosensory receptors, with select odorant receptor genes, including odorant receptor Or117, displaying an opposite dynamic expression pattern. We hypothesized that Or117 acts as a molecular switch, which regulates age- and mating-dependent floral seeking in female Aedes aegypti mosquitoes. Ectopic expression of Or117 in the empty neuron system of Drosophila identified camphor, present in the headspace of the preferred host plant, Lantana camara, as the natural ligand. Targeted knockout of Or117, using CRISPR-Cas9, or the subtraction of camphor, abolished the attraction of teneral females to synthetic floral odor(s), as a result of a lack of antennal response, compared with wild-type mosquitoes. Age, as well as mating, abolished the attraction of wild-type females to floral odor, which was correlated with a differential decrease in sensitivity to camphor, as well as off-and-on responses to several of the constituents of the synthetic L. camara floral odor. As such, this study establishes a direct causal molecular relationship between an odorant receptor and the regulation of resource-seeking behavior in female Ae. aegypti. In the discussion, we postulate how the regulation of odorant receptor expression may provide flexibility in odor coding and ensuing behavior.