Abstract
Mosquito-borne diseases account for the deaths of approximately 700,000 people annually throughout the world, with many more succumbing to the debilitating side effects associated with these etiologic disease agents. This is exacerbated in many countries where the lack of mosquito control and resources to prevent and treat mosquito-borne disease coincide. As populations of mosquito species grow more resistant to currently utilized control chemistries, the need for new and effective chemical means for vector control is more important than ever. Previous work revealed that plant essential oils enhance the toxicity of permethrin against multiple mosquito species that are of particular importance to public health. In this study, we screened permethrin and deltamethrin in combination with plant essential oils against a pyrethroid-susceptible and a pyrethroid-resistant strain of both Aedes aegypti and Anopheles gambiae. A number of plant essential oils significantly enhanced the toxicity of pyrethroids equal to or better than piperonyl butoxide, a commonly used synthetic synergist, in all strains tested. Significant synergism of pyrethroids was also observed for specific combinations of plant essential oils and pyrethroids. Moreover, plant essential oils significantly inhibited both cytochrome P450 and glutathione S-transferase activities, suggesting that the inhibition of detoxification contributes to the enhancement or synergism of plant essential oils for pyrethroids. This study highlights the potential of using diverse plant oils as insecticide additives to augment the efficacy of insecticidal formulations.
Highlights
Synthetic insecticides have proven immeasurably valuable in the fight against economically relevant insects and pests of public-health importance
Numerous plant oils significantly increased the toxicity of permethrin and deltamethrin, two pyrethroids commonly utilized for the control of mosquitoes, and were capable of synergizing pyrethroids in some combinations
This synergism was concentration-dependent and primarily observed in pyrethroid-susceptible mosquito strains challenged in this study
Summary
Synthetic insecticides have proven immeasurably valuable in the fight against economically relevant insects and pests of public-health importance. A select few have been important in mosquito-borne-disease control programs in recent decades [1,2]; in particular, pyrethroids, organophosphates, carbamates, and organochlorines have been main-line defenses against mosquito-borne disease. Resistance to these insecticides has been documented on every continent where mosquitoes are present, and will continue to challenge communities in the coming decades unless new chemistries are explored [1,3,4]. This insecticidal class has relatively low mammalian toxicity, so it can be used in close proximity to people; it is widely used in indoor residual sprays, ultralow volume applications, insecticide-treated bed nets, spatial repellents, and insecticide-treated clothing [8,9,10,11,12,13,14,15]
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