Mosquito-borne diseases are a significant problem for the global community, and result in severe mortality, morbidity, and economic impact to humans, companion animals, and livestock. As such, insecticide resistance is an ever-growing concern of vector control agencies throughout the world. It is imperative that researchers continually develop new strategies for the control of vector species that impact the health of individuals and communities, at large. Plant extracts represent a readily exploitable source of novel insecticidal agents and synergists, especially in light of their accelerated pathway for EPA registration. We investigated extracts of veratrine (V), Sichuan pepper (SP), and black pepper (BP) for biological activity, since they are known to affect voltage-sensitive Na+ channels, presumably at binding sites different from that occupied by pyrethroids. Extracts were dissolved in ethanol and applied to Aedes aegypti adult females for evaluation of their potential lethality alone and in concert with natural pyrethrins (NP) to assess the degree to which they could synergize this natural mosquitocide. Moreover, a significant increase in the toxicity of natural pyrethrins was observed after 24-hr co-exposure with plant extracts. All extracts caused significant block of spontaneous firing of D. melanogaster CNS at low concentrations. Moreover, when co-applied with NP at concentrations that produced no effect alone, V, BP, and SP extracts significantly synergized the neuronal blocking effect of NP on the Drosophila CNS. Surprisingly, PBO significantly enhanced the neuronal blocking effect of natural pyrethrins, a mode of action of this compound not previously documented to our knowledge. These results indicate the potential of plant extracts such as V to enhance insecticide action on the nervous system and that commercial synergists such as PBO might act in unique modalities not previously observed. This study demonstrates the potential of plant extracts to circumvent existing pyrethroid resistance and to synergize the effects of known public health insecticides.

Natural and synthetic compounds display multiple mechanisms of synergism and resistance-breaking properties

2019 Fall National Meeting

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