Effect of four spray regimes on the development of permethrin and dichlorvos resistance, in the laboratory, by the house fly (Diptera: Muscidae).

Abstract

A Musca domestica L. strain possessing latent resistance to pyrethroid insecticides was selected in the laboratory, using four spray regimes involving single selections each generation with either permethrin, dichlorvos, permethrin, and dichlorvos alternated each generation, or a 1:1 mixture of permethrin and dichlorvos. After eight generations of selection, resistance to permethrin at the LC50 level was 73-fold in the permethrin-selected strain, 4-fold in the dichlorvos-selected house flies, 31-fold in the alternately selected strain, and 6-fold in the mixture-selected strain. Dichlorvos resistance was 4-, 27-, 10-, and 7-fold in the respective strains after eight generations. Resistance levels declined in the four strains after the selection pressure was removed. A 10:1 mixture of piper only but oxide and permethrin increased permethrin susceptibility fivefold and reduced heterogeneity in the resistant (permethrin-selected) strain. The feasibility of alternating insecticides, using mixtures, or using synergists to postpone pyrethroid resistance development in the field is discussed.