Pyrethrins elicit olfactory response and spatial repellency in Aedes albopictus

Abstract

BACKGROUND Pyrethrum from dry flowers of Chrysanthemum is a well‐known botanical insecticide and repellent. Its insecticidal activity attributes to its six insecticidal esters, collectively known as pyrethrins. Pyrethrins and its synthetic analogs pyrethroids exert their toxic action by modifying the function of voltage‐gated sodium channels. Aside from insecticidal activity, pyrethrum has also been used to repel mosquitoes for centuries. Today, pyrethrum continues to be used as an active ingredient in mosquito coils and other mosquito‐repellent devices globally. However, the mechanism of pyrethrum repellency remains largely unknown. RESULTS Here we report that pyrethrum vapor induced spatial (non‐contact) repellency in Aedes albopictus, a major vector of dengue and West Nile viruses. Using electroantennogram (EAG) recordings from adult antennae, we found that pyrethrum elicited EAG response in a dose‐dependent manner. We then isolated the six insecticidal esters, pyrethrins I and II, cinerins I and II, jasmolins I and II from pyrethrum extract and discovered that five of the six esters, except jasmolin I, all elicited EAG responses. Furthermore, pyrethrins I and II, cinerin II and jasmolin II induced repellency, whereas cinerin I and jasmolin I did not. CONCLUSION Of the six pyrethrins, four of them, pyrethrins I and II, cinerin II and jasmolin II, activate olfactory‐receptor neurons and elicit spatial repellency in Ae. albopictus. Our study provided a foundation for future structure–function studies of pyrethrins, their cognate olfactory receptors and efficacies of repellency and for the development of new and more effective mosquito repellents for controlling vector‐borne human diseases. © 2021 Society of Chemical Industry.

Natural and Synthetic Pyrethrins Act as Feeding Deterrents against the Black Blowfly, Phormia regina (Meigen)

“…Some level of neurotoxic effects caused by ingestion may contribute to the potency of the feeding deterrence of these compounds. Recent progress in our understanding of olfactory perception [ 57 ] and learning [ 58 ] of pyrethrins and pyrethroids suggests another possibility: that flies can associate the olfactory/taste cues of the insecticides with the negative experience brought on by the toxic effects, to avoid further feeding. Considering the potential of these causal mechanisms, the net feeding deterrence based on oral sensory stimulation should be investigated by an assay system, such as a manual capillary feeding assay [ 34 ], which supports manipulation of the feeding of a single restrained fly and the involvement of sensory organs.…”

Molecular and functional characterization of a conserved odorant receptor from Aedes albopictus

“…The hand-in-cage assay method used was identical to that described previously [ 44 ]. Forty 4- to 9-day-old females (mated, non blood-fed) were transferred to a 30 cm × 30 cm × 30 cm mosquito cage for 24 h prior to assay and were provided only with water in a cotton ball.…”

Understanding the biological action of insecticides is the key to their continuous improvement

“…This paper provides important observations on their effect on behavior and at their target level. The second paper, 12 by Yan, et al ., uses a series of bioassays to show the repellency effects shown by individual structural components of a pyrethrum mixture toward mosquitoes. Both papers contribute important observations of the relationship between chemical structure and repellency and can lead to the development of simpler, more effective repellent strategies for both agriculture and human health.…”