Certain plant essential oils have proven to have the ability to enhance the toxicity of various insecticides, specifically pro-insecticides, which must be first metabolically activated. Organophosphorus insecticides and other pro-insecticides are typically activated by oxidative enzymes in the insect, especially CYP450-dependent monooxygenases. Traditional synergists, such as piperonyl butoxide, inhibit the monooxygenases and usually antagonize the OPs’ and other pro-insecticides’ activities, rather than enhancing them. However, in our studies of plant essential oils, we have determined that some oils and their constituent terpenes can synergize pyrethroids’ activities, but other oils enhance pro-insecticides’ activities. The best oils for enhancing pro-insecticides include cedarwood Moroccan, cedarwood Texas, and thymol. Our hypothesis is that those oil up-regulate genes for CYP450-dependent monooxygenases. RNA sequencing of the surviving female Aedes aegypti mosquitoes that were treated with a plant essential oil or terpenoid was conducted and analyzed to aid in the understanding in how these compounds are acting as synergists. Gene ontology and analysis of the available Aedes aegypti gene mapping reported a number of genes associated with metabolic processes and detoxification are being upregulated as a result of the selected plant essential oil or terpenoid treatments. A validation of the results using qPCR allowed confirmation of the sequencing data, while being able to identify variation in gene expression between types of oil or terpenoid. Cedarwood Moroccan, cedarwood Texas, and thymol were demonstrated to increase oxidative (detoxification) enzymes in Aedes aegypti. One immediate utility is the formulation of an up-regulation oil for use with organophosphate (thiono-type) insecticides, since they require oxidative activation inside the insect.

Impact of plant essential oils on metabolic gene expression in the Yellow Feber Mosquito (Aedes aegypti) has been characterized

ACS Fall 2021

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