November 10, 2021 | The diversity and abundance of freshwater aquatic insects plunges when commonly used neonicotinoid (neonic) insecticides leach into waterways, finds research published in the Proceedings of the National Academy of Sciences. While this is the latest study exploring the effects of neonicotinoids in the field at real-world exposure levels, it is far from the first to show unacceptable hazards to wildlife and ecological health. To determine how neonicotinoids affect critical aquatic species near the bottom of the food chain, researchers created a series of 36 experimental ditches, split into four groups of nine. Mimicking a pulse that may come from a nearby insecticide application, each group of ditches was dosed every two weeks for a period of three months. Scientists collected over 55,000 insects over the course of the experiment. However, overall abundance, biomass, and diversity of insects collected declined in dosed ditches over the three-month period. By the end of the study, compared to the control group overall insect biomass declined by 11, 4, and 50 percent along a gradient of increasing amounts of neonic dosing. “We saw dramatic declines in all the species groups studied, such as dragonflies, beetles and sedges,” said study author Henrik Barmentlo, PhD, both in absolute numbers and in total biomass. “In the most extreme scenario, the diversity of the most species-rich group, the dance flies, even dropped to a single species.” Dr. Barmentlo notes that these effects have major trophic impacts for other wildlife, like birds that rely upon these insects. “So it is quite possible that these bird species suffer from a lack of insects, or in other words: food,” he said. Amphibians are likely to feel the full effect of neonicotinoid contamination, as they are not only exposed through water, but also rely upon a healthy insect population for sustenance. [Barmenio, S. Henrik et al. Experimental evidence for neonicotinoid driven decline in aquatic emerging insects. Proceedings of the National Academy of Sciences. 118 (44):e2105692118. 2021.]
