No evidence that a common pesticide impairs female mate choice in a freshwater amphipod.

Sublethal concentrations of pesticides may drastically alter the evolutionary trajectories of populations by interfering with mating behaviors. We used a median lethal concentration (LC50) experiment to test the sensitivity of three amphipod (Hyalella sp.) classes (females, small males, and large males) to five concentrations [10.4, 1.52, 0.16, 0.05, none detected (ND) microg/L] of the most commonly applied pesticide (malathion) in the United States. We then tested the sensitivity of female mate choice to sublethal concentrations (0.55, 0.38, and 0.05 microg/L) of malathion using a dichotomous choice test. Mortality was relatively high at low concentrations for all three amphipod classes with LC50s ranging from 0.06 microg/L in females to 0.19 microg/L in small males. There was overlap in the 95% CI of these estimates across amphipod classes suggesting no class-specific differences in sensitivity to malathion. We found no evidence that malathion interferes with female choice in this species, suggesting that mating behavior may not always be a good indicator of sublethal pesticide contamination.