Respiratory strategies and associated exchange epithelia as determinants of contaminant uptake in aquatic insects

Aquatic insects are used extensively to evaluate water quality. Despite their widespread use as indicator organisms, relatively little is known about the organismal characteristics that determine sensitivity differences to individual and multiple stressors. Insects have evolved several respiratory strategies that range from breathing atmospheric air to utilizing dissolved oxygen in water via exchange epithelial surfaces. This dissertation examines the role of respiratory attributes in determining differential accumulation of the insecticide chlorpyrifos, and further examines how accumulation rates are affected by temperature shifts. In addition, the relative roles of uptake rates and target site sensitivity differences are examined among developmental stages of the aquatic midge, C. riparius. Major findings: (1) Smaller, gill-bearing insects accumulate chlorpyrifos and water at higher rates than larger, air-breathing insects. (2) Chlorpyrifos and water accumulation rates are highly covariant in aquatic insects. (3) Temperature increases affect chlorpyrifos accumulation rates in dissolved oxygen breathers more so than in air-breathers. (4) Earlier instars of C. riparius are more sensitive to chlorpyrifos than later instars. (5) Sensitivity differences among 2nd–4th instar C. riparius are largely due to differences in chlorpyrifos accumulation rates.