title: Impact of aquatic insect life stage and emergence strategy on sensitivity to esfenvalerate exposure.
abstract: We investigated the impact of aquatic insect life stage and emergence strategy on sensitivity to esfenvalerate, a synthetic pyrethroid insecticide, using field-collected Brachycentrus americanus Banks (Trichoptera: Brachycentridae) and Cinygmula reticulata McDunnough (Ephemeroptera: Heptageniidae) insects. Final-instar C. reticulata emergence was observed for one week following three environmentally relevant, 48-h esfenvalerate exposures (0.005, 0.01, and 0.015 microg/L). Emergence was significantly depressed following exposure to esfenvalerate and resulted from an increase in nymph mortality during the emergence process. This experiment was duplicated for late-instar C. reticulata nymphs, which were similar in size to the final-instar nymphs but were not near emergence. Late-instar C. reticulata mayflies were approximately fivefold less sensitive to esfenvalerate exposures as gauged by one-week mortality rates. Brachycentrus americanus pupal mortality was significantly increased over that in controls following 48-h esfenvalerate exposures of 0.1 and 0.2 microg/L. These response concentrations correlated closely with those for case-abandonment rates of fourth-instar B. americanus larvae (a sublethal effect of esfenvalerate exposure). Pupal mortality rates were approximately 16-fold higher than those observed in larvae. Adult female egg weight as a percentage of total body weight was significantly decreased following pupal esfenvalerate exposures of 0.05, 0.1, and 0.2 microg/L. These findings suggest that exposure to esfenvalerate may impair hemimetabolous insect emergence behaviors and may decrease fecundity in holometabolous aquatic insects.
authors.affiliation: Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Katherine R
authors.initials: KR
authors.lastname: Palmquist
authors.forename: Paul C
authors.initials: PC
authors.lastname: Jepson
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Jenkins
mesh_terms: D000818:Animals; D001681:Biological Assay; D049628:Body Size; D001835:Body Weight; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005260:Female; D007313:Insecta; D007306:Insecticides / Q000633:toxicity; D007814:Larva / Q000187:drug effects*; D009570:Nitriles / Q000633:toxicity*; D009758:Nymph / Q000187:drug effects*; D011722:Pyrethrins / Q000633:toxicity*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000494:pharmacology*
chemical_list: D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; D014874:Water Pollutants, Chemical; C017690:fenvalerate