Pyrethrum, a natural insecticide derived from flowers of Tanacetum cinerariifolium (also known as Chrysanthemum cinerariaefolium), is one of the most widely used botanical insecticides. The principal components of pyrethrum, pyrethrins, and its synthetic analogs pyrethroids exert their toxic action by targeting voltage-gated sodium channels. Beside its insecticidal activity, pyrethrum extract has been used as an effective insect repellent against biting arthropods for thousands of years and, since the beginning of the twentieth century, it has been commercially incorporated into mosquito coils and other mosquito-repellent devices. Despite the longevity of pyrethrum and its global use as an insect repellent, the mechanism(s) of pyrethrum repellency remains a mystery. Over the past several years, we have been taking the molecular genetic, electrophysiological and behavioral approaches to elucidate the molecular basis of pyrethrum repellency in Aedes aegypti. We find that pyrethrins and a minor component, (E)-β-farnesene (EBF), each activate a specific type of olfactory receptor neurons. We identify an odorant receptor (AaOr31) as a cognate Or for EBF and find that Or31-mediated repellency is significantly synergized by pyrethrin-induced activation of sodium channels. Thus, pyrethrum exerts spatial repellency through a novel, dual-target mechanism. Elucidation of this two-target mechanism may have potential implications in the design and development of a new generation of synthetic repellents against major mosquito vectors of infectious diseases.

Dual-target molecular mechanism of pyrethrum repellency against mosquitoes

ACS Fall 2021

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