Neuronal Odor Coding in the Larval Sensory Cone of Anopheles coluzzii: Complex Responses from a Simple System
Anopheles mosquitoes are the sole vectors of malaria and other diseases that represent significant threats to global public health. While adult female mosquitoes are responsible for disease transmission, the pre-adult larval stages of the malaria vector Anopheles coluzzii and other mosquitoes rely on a broad spectrum of sensory cues to navigate their aquatic habitats efficiently to avoid predators and search for food. Of these, mosquito larvae rely heavily on volatile chemical signals that directly activate their olfactory apparatus. Because most studies on mosquito olfaction focus on adults, a paucity of attention has been given to the larval olfactory system, in which the peripheral components are associated with the sensory cone of the larval antennae. To address this, we have investigated the electrophysiological response profile of the larval sensory cone in Anopheles mosquitoes. We found that the larval sensory cone is particularly tuned to alcohols, thiazoles and heterocyclics. Furthermore, these responses can be assigned to discrete groups of sensory cone neurons with distinctive, dose-dependent odorant-response profiles that also provide larvae with the ability to discriminate among compounds with similar chemical structures. A correlation analysis was conducted to determine the relationship between specific larval chemosensory receptors and the response profiles of sensory cone neuron groups. These studies reveal that the larval sensory cone is a highly sophisticated organ that is sensitive to a broad range of compounds and is capable of a remarkable degree of chemical discrimination. Taken together, this study presents critical insights into olfactory coding processes in An. coluzzii larvae that further our understanding of larval chemical ecology and will contribute to the development of novel larval-based strategies and tools for mosquito control and the reduction of vector-borne disease transmission.