Abstract: A housefly (Musca domestica vicina Macquart) strain (DR0) possessing high level resistance to deltamethrin was selected under different insecticide applications in the laboratory, involving alternating insecticide(phoxim), using insecticide mixture(1∶100 mixture of deltamethrin and phoxim) and deltamethrin adding synergist(SV₁). Before generation F₁₆ (F₁₇),the development of resistance to deltamethrin and selecting insecticides was relatively slow in all three strains; but after that, the rate of development increased, especially that of the deltamethrin+SV₁ selected strain to deltamethrin.The changes of susceptibility to deltamethrin were correlated with the selection pressure. Biochemical studies showed that,the changes of enzyme activities or properties of esterase, carboxylesterase, mixed-function oxidase, glutathione-S-transferase and acetylcholinesterase were responsible for the changes of susceptibility in the resistant housefly.

Key words: housefly, resistance, deltamethrin, changes of susceptibility, insecticide application