The use of neonicotinoid pesticides is pervasive in agricultural regions, including the Prairie Pothole Region of North America. There is increasing concern that these pesticides are having harmful effects on non-pest organisms, with particular concern for bees and other pollinators. There use can also potentially have large impacts on freshwater ecosystems, and aquatic insects have been shown to be particularly vulnerable. Neonicotinoids are highly water soluble, and can be transported readily to nearby surface waters.
To investigate the potential impacts of neonicotinoids on prairie wetlands, we conducted an outdoor mesocosm experiment. Twenty 1200 L tanks were inoculated with a homogenized mixture of sediment from nearby wetlands to a uniform consistency of 5 cm depth, and the tanks were filled with water to 925 L in May 2016. After allowing the wetland communities to establish and stabilize, imidacloprid was applied as three repeated pulses, one week apart, into four different treatment types, to simulate pulsed additions into wetlands via rainfall events. Imidacloprid was added at 0.2, 2, and 20 µg/L to each of five replicate tanks, along with 5 control tanks. Plexiglas floating conical emergent traps (diameter 63 cm) were placed on the water surface and adult aquatic insects emerging were captured, identified and enumerated.
Results/Conclusions
Total chironomid emergence was significantly reduced in both the 2 and 20 µg/L treatments compared to control tanks, but no significant difference was observed between the lowest level treatment (0.2 µg/L) and controls. Chironomid diversity, as measured by Shannon’s Index was also significantly reduced in the 20 µg/L treatments compared to control. Treatment pulses were added in June 2016, differences in both mean abundance of emerging chironomids and diversity were observable through August 2016. Our results suggest that repeated short-term contamination of wetland ecosystems by neonicotinoids at low concentration levels could have significant impacts on prairie pothole wetland invertebrate communities, which could have cascading impacts through wetland ecosystems.