The chronic effects of exposure of Culex restuans (Theobald) and Aedes albopictus (Skuse) (Diptera: Culicidae) to low concentrations of malathion were examined by exposing larvae of the two species to four malathion doses at 20, 25, and 30°C and maintaining the resulting adults at 25°C. For both species, a significant temperature by malathion interaction on survival was found. Greater temperatures at the highest malathion dosage had significantly lower survivorship than in other treatments, but this effect was not observed at 20°C. These results suggest that low temperature may buffer against some of the negative effects of malathion. For both species, temperature but not malathion had significant effects on female developmental time to adulthood and adult longevity. Temperature also affected adult female size for Ae. albopictus but not Cx. restuans. Ae. albopictus females developed faster as temperature increased, lived longer when larvae were maintained at 30°C than at 20°C, and were larger when larvae were maintained at 25°C than at 20 or 30°C. Cx. restuans females developed faster at 25 and 30°C than at 20°C and lived longer at 25°C than at 20 or 30°C. The estimated finite rate of increase (λ′) for Cx. restuans was significantly lower at 20°C than at 25 and 30°C, whereas that of Ae. albopictus was significantly influenced by an interaction between temperature and malathion with significantly lower λ′ at 20°C than at 25 and 30°C for all malathion treatments except 0.014 mg liter^-1. Understanding how pesticides interact with abiotic environmental conditions will contribute to management decisions about vector control practices.