A Mechanism of Resistance to Organophosphorus Acaricides in A Strain of the Cattle Tick Boophilus Microplus

Abstract

Radioactive coumaphos, diazinon, cis- and trans-dioxathion, and dioxene derivative of dioxathion individually gave similar results for penetration and metabolism in larvae of an organophosphorus-resistant and an organophosphorussusceptible strain of cattle tick. The phosphorothionates, coumaphos and diazinon, were metabolized to their respective oxygen analogues, diethyl thiophosphate and diethyl phosphate. The dioxathion components, phosphorothiolothionates, were metabolized additionally to diethyl dithiophosphate. The production of cholinesteraseinhibiting oxidation metabolites from the dioxathion components was shown indirectly by the considerable lowering of acetylcholinesterase activity in treated larvae and by assays for enzyme inhibitors in larvae treated with trans-dioxathion_