Muscarinic acetylcholine receptors and their potential as an insecticide target

Reducing arthropod populations with chemical insecticides alleviates the deleterious impacts that arthropods have on agriculture and public/animal health. The widespread and overuse of insecticides has resulted in resistance emphasizing the need to find new molecules that work at novel or underutilized targets. The insect cholinergic system, where acetylcholine functions as the primary excitatory neurotransmitter within the central nervous system (CNS), is an established insecticide target. However, muscarinic acetylcholine receptors (mAChRs) have not garnered as much attention, and while these receptors have been validated as an insecticide target, there are currently no available insecticides using this mode of action on the market. Using the small molecule probe pilocarpine, we are dissecting the function of muscarinic receptors in the CNS where these receptors influence the CNS firing rate. Changes in the firing rate in response to pilocarpine are modified in naturally occurring Drosophila melanogaster strains (e.g., resistant and susceptible strains), but also with the knockdown of muscarinic subtypes using the GAL4-UAS system. Overall, pilocarpine has a biphasic effect on the CNS firing rate in all strains, but there are concentration-dependent changes between the strains. Further, knockdown of the mAChR-B expression affects the time for maximum neuroexcitation to be achieved. While pilocarpine has low oral toxicity to Drosophila melanogaster and Anopheles gambiae, it can synergize the toxicity of GABA-gated chloride channel blockers (e.g., lindane and fipronil). Overall, we propose that the insect muscarinic system could be a valuable insecticide target, especially with a complete