Effect of diazinon selection upon two organophosphorus-resistant field strains of Lutilia Cuprina (Wied.) (Diptera, Calliphoridae)

Abstract

AbstractTwo field strains of Lucilia cuprina (Wied.) of different susceptibilities to diazinon were selected over 25 generations by immersion of first-instar larvae in aqueous emulsions of diazinon for five minutes ; the resistance of the larvae and adult females was compared with a standard laboratory susceptible strain. Resistance increased rapidly in both strains, reaching a maximum for adult females (R.F. = 5–6) in generation 3 and for larvae (R.F. = 46–60) in generation 6. After removal of selection pressure at generation 8 the resistance factor fell to 20–24 by generation 25. Because the resistance mechanisms are known to place their carriers at a disadvantage in the absence of selection pressure, the practical implications of the rapid increase in resistance must await results of experiments with known genotypes.