New Jersey light trap data collected daily from 1977 through 1981 were analyzed to evaluate the efficacy of ground applied ultra-low volume (ULV) malathion against natural populations of Aedes vexans and Culex species mosquitoes. A comprehensive statistical evaluation of the light trap data for the three days before and three days following ULV application demonstrated statistically significant declines averaging 21% in the female population of Ae. vexans and 27% in female Culex species.