Kuechle, K. J., E. B. Webb, D Mengel and A.R. Main. 2022. Seed-treatments containing neonicotinoids reduce aquatic insect abundance in managed floodplain wetlands.
Neonicotinoid insecticides are commonly used as seed-treatments on major agricultural row crops (e.g., corn). Indeed, neonicotinoid treated agricultural crops are often planted directly in floodplain wetlands managed for wildlife, specifically waterfowl. Numerous studies have documented impacts of neonicotinoids to aquatic invertebrates in laboratory and mesocosm settings; however, there is limited information on impacts to aquatic invertebrates in field settings. We investigated invertebrate community response to planting of neonicotinoid-treated seed in managed wetland ecosystems in Missouri. In 2016, we sampled water, sediment, and aquatic invertebrates from 22 paired wetlands during spring (pre-wetland drawdown) and fall (post-wetland flood-up) followed by a third sampling period (spring 2017). During summer, portions of study wetlands were planted with either seed treated corn (treated) or untreated corn (control). Water and sediment concentrations of the three most common neonicotinoids were used to calculate overall neonicotinoids toxicity equivalents (NI-EQs) based on an additive model of neonicotinoids toxic equivalency factors. Mean total NI-EQs for sediment (0.58 μg/kg) were an order of magnitude greater than water (0.02 μg/L). Water quality parameters and insecticide concentrations were used to evaluate effects of neonicotinoid and fungicide concentrations on aquatic macroinvertebrates using a series of generalized linear mixed effects models. Results indicate an overall decrease in aquatic insect richness and abundance with increasing NI-EQs in both wetland water and sediments, as well as a similar negative relationship with sediment fungicide concentration. Post-treatment, treated wetlands had lower insect richness and abundance compared to untreated wetlands, but a recovery in abundance and richness followed in spring 2017. Our results have implications for aquatic invertebrates and wetland-dependent species (e.g., migrating waterbirds) as neonicotinoids, although below lethal concentrations, are impacting wetland ecosystems. Research results will be useful to wetland managers in making decisions regarding use of neonicotinoid seed-treatments, and potentially, provide broader considerations of the role agricultural production has in future wetland management and conservation planning.