Insect repellents mediate species-specific olfactory behaviours in mosquitoes

Area of Science:

• Entomology
• Neuroscience
• Chemical Ecology

Background:

• The precise mechanisms of action for mosquito repellents like DEET are not fully understood.
• Previous studies often generalize repellent effects across mosquito species and focus on attraction rather than direct repulsion.
• Direct examination of mosquito sensory neuron responses to repellents is frequently lacking.

Purpose of the Study:

• To investigate the species-specific repulsive effects of six mosquito repellents on Anopheles coluzzii, Aedes aegypti, and Culex quinquefasciatus.
• To analyze the behavioral and neuronal responses of An. coluzzii to human odorants and repellent mixtures.
• To elucidate the relationship between olfactory neuron activation and repellent behavior.

Main Methods:

• A close proximity response assay was employed to assess the direct repulsive impact of repellents.
• Behavioral assays and calcium imaging of antennae were used to record responses to odorants and repellent combinations.
• Tested repellents included DEET, lemongrass oil, p-menthane-3,8-diol (PMD), and eugenol.

Main Results:

• Anopheles coluzzii were repelled by lemongrass oil and PMD. Aedes aegypti and Culex quinquefasciatus showed repellency to lemongrass oil, PMD, eugenol, and DEET.
• High concentrations of human odorants (1-octen-3-ol, benzaldehyde) acted as repellents and stimulated more olfactory neurons in An. coluzzii.
• Observed changes in olfactory responses to repellent mixtures correlated with changes in repulsive behaviors.

Conclusions:

• Mosquito species exhibit distinct behavioral reactions to repellents, indicating a need for species-specific approaches.
• Elevated odorant concentrations may trigger repellent responses by activating specific sensory neurons or broadly exciting olfactory neurons.
• DEET modulated An. coluzzii responses to PMD but not lemongrass oil, suggesting complex interactions within repellent blends.