A Resistance Mechanism in Organophosphorus-Resistant Strains of Sheep Blowfly (Lucilia Cuprina)

Abstract

After extensive field use of diazinon for control of Lucilia cuprina (Wied.) a 3·1 times resistant (DB) strain appeared (Shanahan 1966). Subsequently a 10 times resistant (G) strain has been found (Shanahan, personal communication). Resistance was confirmed but slightly lower factors of 2·2 and 6 for· the DB and G strains respectively were determined. Studies on penetration and metabolism and acetylcholinesterase inhibition in vivo and in vitro in the resistant strains, DB and G, and in a susceptible strain, LS, were made using [14C]diazinon and unlabelled diazoxon. Sufficient differences were found in in vivo inhibitor levels in the strains following equal diazinon treatment to account for the resistance factors. In add~tion, the thoracic acetylcholinesterase of the G strain was less sensitive to inhibition than those of the other two strains.