Odorant ligands for the CO(2) receptor in two Anopheles vectors of malaria

Exhaled CO(2) is an important host-seeking cue for Anopheles mosquitoes, which is detected by a highly conserved heteromeric receptor consisting of three 7-transmembrane proteins Gr22, Gr23, and Gr24. The CO(2) receptor neuron has been shown to also respond sensitively to a variety of odorants in Aedes aegypti. The detection of CO(2) is important for upwind navigation and for enhancing the attraction to body heat as well as to skin odorants. The orthologs of the CO(2) receptor proteins are present in malaria-transmitting mosquitoes like Anopheles coluzzii and Anopheles sinensis. Activators and inhibitors of the CO(2)-neuron were tested on the maxillary palps in these two species by single-sensillum electrophysiology. The electrophysiological testing of three prolonged-activator odorants identified originally in Aedes aegypti also showed varying ability to reduce the CO(2)-ellicited increase in spikes. These findings provide a foundation for comparing the functional conservation with the evolutionary conservation of an important class of odorant receptor. The identification of a suite of natural odorants that can be used to modify the CO(2)-detection pathway may also contribute to odor-blends that can alter the behavior of these disease transmitting mosquitoes.