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

Abstract

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.