Native Bees are Exposed to Neonicotinoids and Other Pesticides

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Native bees foraging in grasslands and agricultural fields provide ecosystem services through pollination and may play a greater role in the future as honey bee populations decline worldwide. It is unclear how the widespread use of pesticides may affect native bees as they move across the broader agricultural landscape.

USGS scientists initiated a field-based reconnaissance study to determine the exposure of native bees to pesticides. A total of 54 composite samples of native bees were collected over two field seasons from traps in northeastern Colorado in both grasslands and wheat fields. The samples were then tested for 122 different pesticides and 14 pesticide breakdown products.

Nineteen pesticides and breakdown products were detected in native bees from all sites sampled in 2013 and 2014. The neonicotinoid insecticide, thiamethoxam, was the most frequently detected pesticide (present in 46 percent of the samples). Native bees in the non-agricultural grasslands were determined to have at least one of the pesticides measured, which indicates they were potentially exposed to pesticides applied to nearby agricultural areas. Pesticide concentrations and detections were generally less in bees collected in grasslands with a smaller percentage of active agriculture within 1 kilometer, which is the maximum foraging distance for native bees. As a result, it seems that the land cover surrounding the agricultural fields could be an important factor for consideration in conservation planning.

Although overall toxicity of these pesticides to native bees is unknown, the chemicals do not have to kill the bees to have an effect. For example, neonicotinoids can cause a reduction in population densities and reproductive success, and impairing the bees' ability to forage. Insecticides and fungicides can also increase a bee's susceptibility to disease and parasites.

The pesticide residues documented in native bees in this preliminary field-based reconnaissance study provides critical information necessary to design more focused research on exposure, uptake, and accumulation of pesticides relative to land use, agricultural practices, and pollinator conservation efforts on the landscape.

This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), USGS Wildlife: Terrestrial and Endangered Resources program and the U.S. Department of Agriculture Farm Service Agency.