Effects of esfenvalerate on native macroinvertebrates representative of Pacific Northwest streams Public Deposited



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  • Aquatic insects are essential components of healthy stream ecosystems, contributing to nutrient cycling, trophic dynamics and other ecological functions. Aquatic insect species, particularly those in the orders Ephemeroptera, Plecoptera and Trichoptera (EPT taxa) are however, extremely sensitive to insecticide contamination. Given that urban and agricultural use of synthetic pyrethroid insecticides are increasing, there is concern that aquatic contamination by these compounds may pose a risk to aquatic insect species. The overarching hypothesis of this research is that specific aquatic insect life history attributes may increase their susceptibility to synthetic pyrethroid insecticides, through an exacerbation of toxic effects and/or enhancement of exposure. The goals of this work were (a) to determine if egg morphology affects esfenvalerate sensitivity, (b) to ascertain the impact of dietary exposure to esfenvalerate among different functional feeding groups, (c) to determine the effect of esfenvalerate intoxication on larval caddisfly case maintenance, and (d) to establish the effects of late-stage esfenvalerate exposure on emergence. Four different aquatic insect species were utilized during the course of these studies; Cinygmula reticulata McDonough (Ephemeroptera: Heptageniidae), Hesperoperla pacifica Banks (Plecoptera: Perlidae), and Brachycentrus americanus Banks (Trichoptera: Brachycentridae) were used in the majority of the experiments. Baetis sp. (Ephemeroptera: Baetidae) egg clutches were utilized as a surrogate for the difficult-to-obtain C. reticulata eggs. Esfenvalerate toxicity testing with aquatic insect eggs indicated that 48h esfenvalerate exposures ranging between 0.07 and 0.5 μg/L caused significant Baetis sp egg mortality. Exposure to lower concentrations immediately preceding hatch resulted in behavioral aberrations in first instar mayflies. The gelatinous clutch structure of caddisfly eggs proved to be the most susceptible egg morphology tested, with significant within-clutch mortality occurring following esfenvalerate exposures of 0.035 μg/L. No toxic effect was observed in H. pacifica eggs exposed to up to 1.0 μg/L esfenvalerate. Esfenvalerate-contaminated food caused adverse effects in both C. reticulata and B. americanus insects, but not in H. pacifica nymphs. A significant decrease in growth was observed in small C. reticulata nymphs reared on 0.05 μg/L esfenvalerate-exposed algae, and a decrease in egg production in final-instar nymphs reared on 0.1 μg/L esfenvalerate-exposed algae. Diet items exposed to esfenvalerate concentrations ranging between 0.5 to 1.0 μg/L induced case-abandonment in fourth-instar B. americanus larvae. None of the aquatic insect species differentiated between esfenvalerate-contaminated and clean food sources during feeding. 48h waterborne exposures of 0.05, 0.1, 0.2, and 0.4 μg/L esfenvalerate also caused fourth-instar larvae to abandon cases, and impaired their ability to rebuild these protective structures. Finally, C. reticulata emergence was disrupted by esfenvalerate exposures ranging from 0.005 to 0.015 μg/L, resulting in significant mortality. B. americanus pupal exposures of 0.05, 0.1, and 0.2 μg/L esfenvalerate significantly reduced successful adult emergence and resulted in decreased egg weight of emerged females. A comparison of life stage esfenvalerate sensitivities of C. reticulata and B. americanus reveals that analogous life stages did not exhibit the same relative susceptibilities, with final-instar nymphs the most sensitive C. reticulata life stage tested, and egg clutches as the most sensitive B. americanus life stage.
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