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_

Acetylcholinesterase Insensitivity in the Biarra Strain of the Cattle Tick Boophilus Microplus, as a Cause of Resistance to Organophosphorus and Carbamate Acaricides

“…The appearance of an organophosphorus-resistant "M" strain prompted investigation by Lee and Batham (1966) who demonstrated greater insensitivity of acetylcholinesterase to inhibition in vitro in larvae of this strain than in larvae of a susceptible reference strain. Larvae of the resistant Ridgelands strain, similar in origin to the "M" strain, were shown by Schuntner, Roulston, and Schnitzerling (1968) to possess acetylcholinesterase less sensitive to inhibition in vivo compared with that in larvae of the susceptible reference Yeerongpilly strain. As no marked differences were observed in studies of penetration and metabolism of organophosphorus acaricides in these two strains, the authors concluded that relative insensitivity of acetylcholinesterase to inhibition in the Ridgelands strain was the cause of resistance.…”

Acetylcholinesterases of blood-feeding flies and ticks

“…Emergence and increasing incidence of tick resistance to OP exposure in Mexico and other countries threaten the US cattle industry and complicate efforts by the CFTEP to maintain an effective entry barrier and to eradicate outbreak infestations [7]. The major mechanism of resistance to OP acaricides in ticks was biochemically characterized as AChE insensitivity to OP inhibition in extracts of tick synganglia [8][9][10] and resistance may also have a metabolic detoxification component [11].…”

Inhibitor profile of bis(n)-tacrines and N-methylcarbamates on acetylcholinesterase from Rhipicephalus (Boophilus) microplus and Phlebotomus papatasi

“…OP insecticides, such as coumaphos, are inhibitors of AChE (EC 3.1.1.7), a serine hydrolase responsible for terminating nerve signals at the synapses of cholinergic systems within the central nervous system of invertebrates, leading to death [15]. OP and pyrethroid resistance has been attributed to both metabolic and target site mechanisms, with the later being the primary reason for OP resistance [12, 16, 17, 18, 19]. OP-insensitive AChE might provide cross resistance to insecticides with similar mode of action, such as carbamates.…”