Abstract: Two housefly strains possessing moderate and high level resistance to deltamethrin were selected in laboratory under different strategies of pesticide applications, involving rotation, combination and addtion of synergist. The results revealed that resistance evolution of the housefly strain with moderate resistance level to deltamethrin was delayed by rotation and combination of insecticides. For the other housefly strain with high level resistance to deltamethrin, development of resistance to deltamethrin and selected insecticide was relatively slowed down by combination of insecticides. Resistance of two housefly strains to deltamethrin declined without contact with any insecticide, but the susceptibility to deltamethrin seems difficult to recover completely.