Botanical pesticides: identification of a molecular target and mode of action studies

Abstract

<p>Mosquitoes and ticks are vectors of several diseases that affect both humans and animals. Control of mosquito-borne and tick-borne diseases has primarily been achieved with the use of chemical insecticides/acaricides. However, an increase in public concern about the safety of conventional synthetic compounds, along with growing insecticide/acaricide resistance, has resulted in a need to find alternatives to control ticks and mosquitoes. In this dissertation I report on the functional and pharmacological characterization of a tyramine receptor from the southern cattle tick (<em>Rhipicephalus microplus</em>). Additionally, I report on the role of botanical essential oil terpenoids to interact with the southern cattle tick's tyramine receptor. Physiological studies of the southern cattle tick's tyramine receptor, using post-transcription gene silencing, show that the southern cattle tick's tyramine receptor is a target that can result in tick mortality. The significance of these results is the reclassification of the southern cattle tick's tyramine receptor (previously thought to be an octopamine receptor), the identification of a potentially novel target of plant terpenoids in the southern cattle tick and an explanation for the potential role of formamidine resistance, which has been reported in the southern cattle tick. Finally, I present the ability of essential oils to enhance the toxicity and/or knockdown of the synthetic pyrethroid permethrin, against two mosquito species (<em>Aedes aegypti</em> and Anopheles gambiae</em>). The enhancement of toxicity and knockdown is similar to, but in many cases, better than the commercial synergist piperonyl butoxide (PBO). The significance of these findings includes the ability to use natural control measures to replace PBO, which has been under scrutiny for non-target toxicological issues.</p>