Laboratory work has shown that mosquitoes obtaining blood meals from animals treated with ivermectin exhibit lowered adult survival, fecundity, egg hatch and larval survival. Computer simulation evaluated the consequences of this phenomenon in field populations of Psorophora columbiae feeding on cattle in the rice agroecosystem. Results suggest that rather minor reductions, on the order of 10% below normal, in these life history parameters would significantly affect the population dynamics of this species in this particular system. Significant reductions in the amount of insecticide used for mosquito abatement are also projected.