Organophosphate Pesticides Alter Blue Crab (Callinectes sapidus) Behavior in Single and Consecutive Exposures

Insecticide effects on nontarget organisms most commonly involve measuring mortality after single exposures. We examined sublethal effects of consecutive exposures of malathion, an organophosphate insecticide used for mosquito abatement, on the behavior of blue crabs (Callinectes sapidus). We measured righting time (i.e., time to return upright when placed upside down), eyestalk reflexes, foraging ability, and response to predation risk in three malathion treatments of 50 µg/L that varied in duration: (1) static exposure for 96 h followed by a second exposure for 96 h, (2) static exposure for 96 h followed by transfer to pesticide-free water for 96 h, (3) control without malathion for 192 h. Malathion significantly increased crabs' righting time 45 ± 23%, but righting time was not different from controls after crabs were placed in malathion-free water for 96 h. Normal eyestalk reflexes significantly declined 50 ± 15% in adults and 75 ± 40% in juveniles. Malathion affected foraging ability; blue crabs sought food more frequently, even in the presence of alarm cues from injured crabs but were less able to locate food after malathion exposure. Thus malathion, at environmentally occurring concentrations, interfered with blue crabs' neuromuscular function, inhibited their ability to forage, and caused them to ignore predation risk when foraging. However, two exposures to malathion did not increase mortality nor further impair behavior, and behavior was not different than controls crabs when placed in seawater without insecticides for 96 h, suggesting sublethal impairment from malathion was reversible.