Formic acid: A neurologically active, hydrolyzed metabolite of insecticidal formate esters

Abstract

Formate esters have potential uses as insecticides in both grain fumigation and public health pest management. This research investigated the hydrolytic metabolism and neurological effects of formate ester compounds. Studies were conducted using Drosophila and houseflies as models for other dipteran pests of medical importance. Results indicated significant formic acid liberation from a broad range of formate esters, both in vivo and in vitro. Based on these initial observations, we subsequently investigated neurological effects of formic acid on the larval housefly nervous system. We found that formic acid caused significant neuroexcitation at concentrations lower than previously shown for inhibition of insect cytochrome c oxidase; however, this conclusion does not preclude that mitochondrial effects may also be occurring in non-nervous tissues. Finally, we investigated formate ester hydrolysis by A- and B-type esterases commonly considered in pesticide detoxification research; however, no significant interactions could be identified, suggesting that as yet unidentified carboxylesterases play roles in formate ester hydrolysis. These findings provide information on formate ester metabolism and modes of action, as well as rationale for further studies on formate ester neurotoxicology and mechanisms of selective toxicity.