Age-dependent perception of floral emissions and the role of CO2 in regulating nectar-seeking in mosquitoes

Mosquitoes require access to nectar for energy and reproduction, a behaviour which varies depending on adult maturation and gonotrophic cycle. To locate and discriminate among nectar resources, mosquitoes may make use of various floral emanations, including volatile organic compounds and carbon dioxide (CO2). In order to identify the bioactive volatile organic compounds (VOCs) in one of the preferred host plants of Anopheles mosquitoes, Lantana camara, combined electrophysiological and chemical analyses were performed using ectopically expressed Anopheles coluzzii odorant receptors (Ors) in the empty neuron system of Drosophila. When presented as a synthetic odour blend, and controlled for the detected ratio and emission rate of individual VOCs, the blend elicited an age- and dose-dependent attraction of An. coluzzii and of the closely-related Anopheles arabiensis. Lantana camara demonstrated a differential circadian emission of CO2, which directly correlated with the volume of nectar secreted. Behavioural assays designed to determine the role of ecologically-relevant concentrations of CO2 in regulating nectar seeking, demonstrated a context-dependency, emphasizing that CO2 is used for close-range floral discrimination during foraging. This study demonstrates a mechanism regulating the detection and perception of ecologically-relevant information by mosquitoes during sugar seeking.