Ivermectin impacts the life history strategy of Chaetopteryx villosa

Freshwater ecosystems are exposed to a wide range of pollutants, including veterinary pharmaceuticals. Among those pharmaceuticals, ivermectin, an antiparasitic compound, has received increasing attention over the last decades due to its high ecotoxicity, with effects being reported in the sub ng/L range. While several orders have been investigated for their sensitivity to ivermectin, Trichoptera, a species-rich and ecologically significant insect order, have largely been overlooked. Here we assessed acute (7 days) and sub-chronic (5 weeks) (mortality, feeding rate, growth and fatty acid (FA) profile) effects induced by ivermectin in Chaetopteryx villosa, a common Trichoptera species in central Europe. Tested ivermectin concentrations ranged from 10 to 10,000 ng/L and 75 to 2,400 ng/L in case of the acute and sub-chronic toxicity test, respectively. LC₅₀ values declined from 2.81 µg/L after 7 days of exposure to 0.74 µg/L after five weeks. Moreover, ivermectin exposure resulted in a strong concentration-dependent reduction in growth assessed by changes in their dry weight (i.e., of 60 % at 300 ng/L, 54 % at 600 ng/L, 100 % at 1,200 ng/L compared to the ivermectin-free control), an observation likely driven by a significantly reduced feeding activity. Moreover, concentrations of individual FAs in C. villosa larvae were significantly reduced at 300 and 600 ng/L, while lower concentrations tended to increase concentrations of several FAs. Similarly, ivermectin significantly affected FA profile and the relative contribution of saturated, monounsaturated and polyunsaturated FAs. Overall, our results demonstrate concentration- and time-dependent effects of ivermectin on key life-history traits of C. villosa potentially leading to effects in aquatic food webs through the shift in FA profiles.