Insecticidal and synergistic potential of three monoterpenoids against the Yellow Fever mosquito, Aedes aegypti (Diptera: Culicidae), and the house fly, Musca domestica (Diptera: Muscidae)

Authors: BAKER, OSHNEIL - University Of Florida; Norris, Edmund; BURGESS, EDWIN - University Of Florida

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2023
Publication Date: 4/5/2023
Citation: Baker, O.S., Norris, E.J., Burgess, E.R. 2023. Insecticidal and synergistic potential of three monoterpenoids against the Yellow Fever mosquito, Aedes aegypti (Diptera: Culicidae), and the house fly, Musca domestica (Diptera: Muscidae). Molecules. 28:3250. https://doi.org/10.3390/molecules28073250.
DOI: https://doi.org/10.3390/molecules28073250

Interpretive Summary: Resistance to the limited number of insecticides registered for use against medical and veterinary arthropod pests threatens public health and food safety, worldwide. Pyrethroids, organophosphates, carbamates, neonicotinoids, and spinosyns are some of the most commonly used chemical classes in medical and veterinary pests, all with documented combinations of target site resistance, enhanced metabolic detoxification, reduced cuticular penetration and behavioral resistance. Synergists are useful additives in insecticidal formulations, except no new synergists have been developed and adopted recently. We set out to investigate the intrinsic toxicity and synergistic potential to enhance both permethrin and methomyl of three monoterpenoids, menthone, fenchone, and carvone. These were screened on both adult yellow fever mosquitoes and house flies. While these terpenoids were not as toxic as currently utilized synthetic insecticides, they did produce strong synergism of permethrin on both mosquitoes and house flies. These results indicate that these select terpenoids may be useful active ingredients and/or synergists in future insecticidal formulations.

Technical Abstract: Resistance to the limited number of insecticides registered for use against medical and veterinary arthropod pests threatens public health and food safety, worldwide. Pyrethroids, organophosphates, carbamates, neonicotinoids, and spinosyns are some of the most commonly used chemical classes in medical and veterinary pests, all with documented combinations of target site resistance, enhanced metabolic detoxification, reduced cuticular penetration and behavioral resistance. Synergists are useful additives in insecticidal formulations, except no new synergists have been developed and adopted recently. We set out to investigate the intrinsic toxicity and synergistic potential to enhance both permethrin and methomyl of three monoterpenoids, menthone, fenchone, and carvone. These were screened on both adult Aedes aegypti and Musca domestica. Of the three monoterpenoids screened, menthone and fenchone were the most toxic with similar LD50 (Aedes aegypti: menthone – 7100 ng/mg and carvone - 7300 ng/mg; Musca domestica: menthone – 6800 ng/mg and carvone – 4300 ng/mg). This was followed by fenchone which was approximately 2-times less toxic than the other two terpenoids (Aedes aegypti: fenchone – 11300 ng/mg; Musca domestica: fenchone – 13200 ng/mg). All monoterpenoids were capable of synergizing permethrin on both Aedes aegypti and Musca domestica adults (co-toxicity factors ranging from 48.4-160). While we were not able to establish a topical dose-response curve for methomyl on Musca domestica, we demonstrated that carvone was capable of synergizing methomyl (co-toxicity factor = 24) when applied 2µg per insect in combination with methomyl. We further explored the ability of these monoterpenoids to inhibit acetylcholinesterase in both mosquitoes and flies, but little-to-no enzyme inhibition was observed at concentrations as high as 1 mM. These results indicate that these select terpenoids may be useful active ingredients and/or synergists in future insecticidal formulations. Their action is also likely due to a mechanism other than action at the acetylcholinesterase enzyme.