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Scientists Examined Native Pollinator Exposure Risk to Neonicotinoids in Native Prairie Strips

samping flume and rain gage - corn field is in the backgroud
Sampling flume and attached rain gage used by the scientists to sample surface water runoff in a riparian strip adjacent to a corn field. The field in the background had a history of being planted with neonicotinoid-treated seeds. Photo Credit: Iowa State University.

Neonicotinoids were not detected in native prairie plants placed next to agricultural fields several years after discontinuation of neonicotinoid seed treatment. In addition, neonicotinoid concentrations were lower or absent in soils and runoff at sites with the native prairie strips.

Conservation practices such as native prairie strips, which are vegetated buffers along stream corridors, and grasslands with native plants interspersed throughout agricultural areas, provide refuge and food sources for terrestrial animals and pollinators. They also have been reported to serve the complimentary purpose of limiting offsite transport of water, sediment, and pesticides from agricultural fields, and thus have the potential to limit non-target aquatic organism exposure in downstream water sources.

Neonicotinoids are highly water soluble and can be transported offsite through runoff as documented in previous U.S. Geological Survey (USGS) studies by their frequent detections in streams across the United States and more specifically in areas of corn and soybean production in the Midwest.

Neonicotinoids are widely used insecticides that are commonly applied as seed coatings to protect agricultural crops from insect pest damage. Plants take in neonicotinoids and distribute them throughout plant tissues where target insects are exposed. These insecticides may be taken in by non-target insects, including pollinators, from plants in treated agricultural fields, or adjacent plantings such as native prairie strips that lie between agricultural fields and streams. Neonicotinoids are reported to cause a variety of effects to native pollinators including reduction in populations and reproduction, impairment of foraging success and development, and increased susceptibility to disease and parasites.

A previous USGS study in Colorado during 2013-2014, documented that native bees were exposed to pesticides collected in wheat fields and to a lesser extent in the adjacent grasslands depending on the proximity of grasslands to treated fields. In this current study, the scientists are setting out to understand if native prairie strips can limit the transport of neonicotinoids from agricultural fields and increase pollinator habitat without exposing them to contaminants through plant utilization.

Scientists measured neonicotinoid residues in local groundwater, surface water runoff, soil, and plants in native prairie strips adjacent to corn and soybean crop fields with a history of neonicotinoid-treated seeds during 2008 to 2013 in the Neil Smith Wildlife Refuge. Samples from six sites with the same crop management history, three with and three without in-field native prairie strips, were collected in 2015–16, 2–3 years after neonicotinoid (clothianidin and imidacloprid) seed treatments were last used.

Neonicotinoids were not detected from root, leaf, or flower tissues associated with the native prairie strips, indicating a low likelihood of exposure to native pollinators and other insects visiting these plants. Sites with native prairie strips had lower concentrations of neonicotinoids in groundwater, had less frequent detections of neonicotinoids in surface water runoff, and rarely had detectable neonicotinoids in soils located at the foot slope of the native prairie strip compared to sites without native prairie strips.

This study provides information about neonicotinoids in native prairie strips 2-3 years following the cessation of treated seed use. However, it does not address pesticide contents of plants during active pesticide use. Measuring neonicotinoid occurrence in pollinators and plants within native prairie strips in agricultural watersheds with current neonicotinoid use represents a potential next step to understand native pollinator exposure risk.

USGS is continuing to build a foundation to understand actual as opposed to perceived risks of pesticide exposure and effects for non-target aquatic and terrestrial organisms. Understanding the actual as opposed to the perceived risks of contaminants provides the information needed to better prioritize research and balance the economic and health needs of the Nation.

This work was supported by the USGS Toxic Substances Hydrology Program and U.S. Department of Agriculture National Institute for Food and Agriculture (IOW5249 and IOW5423). The U.S. Fish and Wildlife Service supported field experimentation and data collection at Neal Smith National Wildlife Refuge.

Reference

Hladik, M.L., Bradbury, S., Schulte, L.A., Helmers, M., Witte, C., Kolpin, D.W., Garrett, J.D., and Harris, M., 2017, Neonicotinoid insecticide removal by prairie strips in row-cropped watersheds with historical seed coating use: Agriculture, Ecosystems and Environment, v. 241, p. 160-167, doi:10.1016/j.agee.2017.03.015.

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