Dazed and Confused: How Insecticide Mixtures Alter the Behavior of the Blue Crab (Callinectes sapidus)

The use of insecticides in the United States for pest control is extensive. Research has primarily focused on the lethal and sub-lethal effects of individual insecticides on non-target species, though evidence indicates that organisms are exposed to multiple insecticides and other toxicants simultaneously. For this project, the blue crab (Callinectes sapidus) was used to investigate the synergistic effects of three insecticides: Carbaryl, Malathion and Resmethrin. All three insecticides are commonly used throughout the United States and represent three different classes of insecticides. To ascertain the baseline effects of each insecticide, blue crabs were exposed to each insecticide separately, at increasing concentrations (10 ppb, 100 ppb and 1 ppm). Then crabs were exposed to different combinations of the insecticides to investigate synergistic effects.  Reflex actions and neurological functioning were assayed every 12 hours, for each surviving crab during each experiment, to quantify the sub-lethal effects of the insecticides. Preliminary data indicates that exposure to pesticide mixtures results in a higher mortality rate and decreased neurological functioning in comparison to the single-pesticide exposures. The blue crab plays an important predatory role in many estuarine systems, and is a valuable commercial fishery. These results indicate that toxicant exposure may have harmful effects on estuarine food webs and may decrease food resources for humans, as insecticides negatively affect the behavior of the blue crab. Ultimately, understanding how multiple insecticides may alter blue crab behavior and survivorship may prove vital for the proper management and protection of this species and estuarine systems.