Larval rearing temperature influences the effect of malathion on Aedes aegypti (Diptera: Culicidae) life history traits and immune responses

The effects of anthropogenic chemical contaminants on aquatic organisms are largely influenced by underlying environmental conditions. We evaluated how larval rearing temperature influences the impact of malathion on the fitness of the yellow fever mosquito Aedes aegypti. Larvae were exposed to three malathion concentrations (0.0 mg/L(control), 0.03 mg/L, and 0.05 mg/L)) at 20, 25 and 30°C and survival to adulthood, development time to adulthood, female fecundity and expression of genes encoding two antimicrobial peptides (defensin, cecropin) and an iron-binding protein (transferrin) quantified. High malathion concentrations at 25°C and 30°C resulted in significantly lower survival to adulthood compared to control and low malathion dose but this effect was not observed at 20°C. Female development time to adulthood was inversely proportional to temperature and was significantly shorter in high malathion dose than in control and low malathion dose at 25°C and 30°C but not at 20°C. Regardless of temperature treatment, females from high malathion dose were significantly larger and laid more eggs than their counterparts in control and low malathion dose. Relative to the controls, at least two immune genes were significantly over-expressed in adult females from malathion-exposed treatments at 20°C (defensin and cecropin) and 25°C (defensin and transferrin) and one gene (defensin) was significantly under-expressed at 30°C. These findings indicate that larval rearing temperature can modify the effect of malathion on fitness traits in mosquitoes.