Resistance to two organophosphorus insecticides in New Zealand populations of the Australian sheep blowfly, Lucilia cuprina.

A treated-surface test was used in a bioassay to detect insecticide resistance to the organophosphorus compounds diazinon and propetamphos, in larvae of field strains of Lucilia cuprina in New Zealand during 1990/91 and 1991/92 (December-April). Mean LC50s for both diazinon and propetamphos showed a significant increase between seasons although this is not necessarily indicative of a trend. Mean LC50s for diazinon increased from 1.16 to 1.60 mg/l (P < 0.001) and for propetamphos from 0.49 to 0.59 mg/l (P < 0.005) in pooled populations. Diazinon and propetamphos resistance was significantly correlated in both seasons, suggesting side-resistance between the two insecticides.