Copper Accumulation Through Diet Versus Direct Water Exposure Routes in a Dragonfly Nymph/Mosquito Larvae Laboratory Food Chain

Abstract

Aquatic organisms can uptake metals directly from contaminated water or by consuming contaminated prey. Knowing the relative importance of these routes is critical to understand how metals enter and move through aquatic food webs. We previously established that nymphs of the aquatic dragonfly Erythemis simplicicollis accumulate elevated copper (Cu) concentrations when living in contaminated wetlands, but the route of uptake was not identified. In this study, we evaluate copper accumulation with a model two-trophic-level laboratory food chain comprised of E. simplicicollis dragonfly nymphs as predators and Aedes aegypti mosquito larvae as prey to gain better insight into Cu accumulation dynamics in these aquatic insect predators. Treatments consisted of dragonfly nymphs exposed to copper through diet (A. aegypti larvae prey exposed to 100 µg/L Cu-contaminated water), water (100 µg/L Cu), diet + water, and a control. Each treatment included 15 replicates, and 10 pretreatment nymphs were analyzed. Exposures lasted 32 days or until nymph death. Copper accumulation in nymphs and nymph mortality was compared among treatments. Eating contaminated prey did not elevate copper concentrations in E. simplicicollis. In contrast, highest copper concentrations accumulated in E. simplicicollis when exposed to contaminated water, in both the water-only and in the diet + water treatments. Additionally, mortality was greater when exposed to copper-contaminated water. Even though the nymphs did not trophically accumulate Cu, direct uptake of Cu from water provides a point of Cu entry into a food chain.