The influence of a neonicotinoid insecticide on aquatic organisms and their interactions

Jesse C Miles, Purdue University

Abstract

Pesticides are one of the most powerful tools used in agriculture to reduce pest populations, protecting crop yield. Of the large number of patented chemical pesticides, neonicotinoids are now the most widely used globally. Neonicotinoids are merited for their application as a prophylactic seed coating and chemical structure that is highly specific to invertebrates. In the US alone, public data has estimated 33-44% of soybeans, and 79-100% of corn acreage were treated with neonicotinoids in 2011. Research on these compounds has examined their potential effects on non-target organisms, namely pollen feeding insects. Most studies, however, have focused on terrestrial species and their ecosystems. The low soil binding and high water solubility of these compounds, paired with their prophylactic use, puts aquatic environments at high risk for contamination via runoff events. Our study sought to assess the potential threat of these compounds to wetland ecosystems via a three-step, hierarchical approach: 1) Determine basic toxicity levels (LC50s) of clothiainidin, a neonicotinoid compound, to a representative suite of wetland organisms, 2) Test behavioral responses of organisms at sublethal levels of the same compound, and 3) Use a replicated mesocoms experiment to determine the impacts of this compound on wetland community food webs. We found a wide range of LC50 values among the species tested. For invertebrates (i.e. Daphnia, odonates, hemipterns, Orconectes, Graphoderus) toxicity values ranged from 0.015 ppb to 46.04 ppb. However, freshwater snails and amphibian larvae showed high tolerance to the chemical with no mortality observed at the highest dissolvable concentration of the insecticide (327 ppm). To test sublethal responses, we measured feeding behavior, movement, and response to stimulus across concentration levels. Our results were both species- and dose-dependent. We observed reduced the feeding rates of water bugs (Belostoma flumineum) in a dose dependent manner but had no effect on crayfish feeding. For amphibian larvae ( Lithobates pipiens), clothiainidin exposure reduced activity levels but only at the highest dissolvable concentration of the insecticide (327 ppm). Lastly, the crayfish O. propinquus exhibited reduced responsiveness to stimulus with increasing clothiainidin concentration. In our community-level experiment we used three clothianidin concentrations (0 ppb, 10 ppb, and 500 ppb). We observed high invertebrate predator mortality with increases in the clothianidin concentration and mortality was 50% higher at 500 ppb compared to 0 ppb. With increased predator morality, prey survival increased by 50% in the highest clothianidin treatment. These mortality increases, paired with low overall prey mortality with predators absent indicate a reduction in predator pressure as levels of clothianidin increase. Our tiered approach demonstrates that laboratory based experiments can be successfully used to make predictions at larger, community level processes. Collectively, our results suggest that exposure to neonicotinoids in aquatic ecosystems could lead to altered food web dynamics and, in turn, modified ecosystem function.

Degree

M.S.

Advisors

Hoverman, Purdue University.

Subject Area

Ecology|Environmental Health

COinS