Declines in populations of bees, mayflies, butterflies and birds have been reported in the recent years and environmental quality is a primary cause. Loss of habitat is also contributing to reductions of grassland birds but the quality of habitat including availability of food and clean water are also causal. Sixty-three years ago, Rachel Carson wrote about a similar phenomenon regarding DDT in her seminal book Silent Spring.
What is causing these changes today? One reason is the use of neonicotinoid pesticides, often shortened to “neonics,” both in agriculture on field crops, vegetables, fruit, and trees, but also in urban settings on lawns, and in homes and garden centers. Neonicotinoid use has become widespread over the last 25 years and is exacerbated by their ready solubility in surface and ground water systems. Five neonicotinoid pesticides are registered for use in Wisconsin: Clothianidin, Dinotefuran, Acetamiprid, Imidacloprid, and Thiamethoxam. Clothianidin, Imidacloprid, and Thiamethoxam are used in production agriculture while Dinotefuran and Acetamiprid are used primarily on turf, in greenhouse operations and homes.
Many seeds and most corn seed today are coated with these compounds as a prophylactic measure to protect seed from insect damage. One corn seed can carry about a milligram of neonicotinoids and the lethal dose for one bee is ~5 nanograms. The coating on one seed can potentially kill as many as 100,000 bees and a typical corn field is planted with 30,000 corn seeds. In 2024, four million acres of corn were grown in Wisconsin of the 91.5 million acres cultivated in corn in the U.S. In addition, corn production has nearly doubled in the U.S. in the last 20 years to meet the demands of the Renewable Fuel Standard to produce ethanol. The North Central region, which includes Wisconsin, is the primary locus of corn production in the U.S.
Neonic effects permeate all biota. Water washes off the neonic seed coating into soil and water systems, negatively affecting the soil organisms, insects, wildlife, and plants that make use of this water to live. The chemicals can also be sprayed on plants or added in granular form to soil. These compounds travel systemically in the plant and can be present in the flowers and nectar and pollen that insects like bees and butterflies seek. The tainted water ends up in streams and rivers and lakes, ground water systems, and in some wells. Recent surveys by the Wisconsin Department of Natural Resources identified neonicotinoids in our water across the state where agricultural activity is found. Five percent of wells tested were also found to contain these chemicals.
The presence of neonicotinoids on seed and in our water systems is impacting wildlife both directly and indirectly. Birds such as cranes readily eat the coated corn seed. The Mississippi River Watershed encompasses much of Wisconsin with the Wisconsin River as a major tributary. Studies on mayfly tissues in the Upper Mississippi River have demonstrated the widespread presence of neonicotinoids. Mayfly emergence has also declined in recent years all pointing to neonicotinoids as the cause. Mayfly larvae are an important food source for fish and other wildlife, spreading the impact of neonics.
Impacts on human health are still under study but existing findings are worrisome. Neonicotinoids target the nervous system of many organisms including humans. The WI Department of Human Health Services has issued a health advisory that recommends a limit in drinking water of 0.2 parts per billion (ug/L) Imidacloprid with higher thresholds for other neonics. Nine percent of WI ground water samples tested exceed this limit for Imidacloprid.
Where do we go from here? Several states have imposed regulations to limit neonicotinoid use mostly at the residential level. New York and Vermont recently enacted the most stringent laws in the United States to ban most uses of these pesticides unless the need is justified. In 2018 the European Union banned outdoor uses of the three primary neonicotinoids Clothianidin, Imidacloprid, and Thiamethoxam. Acetamiprid can still be used until 2033, but recent studies have brought new concerns about its safety. Despite acknowledging many environmental impacts such as the decline of bees and birds, the EPA has yet to issue comprehensive final rules for neonic use. Elected officials in Wisconsin recently attempted to limit use of neonicotinoids on DNR lands and to pass a set of bills to protect pollinators in Wisconsin without success.
Studies on corn and soybean production have shown that neonicotinoid use has little benefit to growers. The provinces of Ontario and Quebec, Canada limit use on these crops to certain situations and requires proof of need in a growing season. Growers in Quebec went from 100% to a few percent use of the coated corn seed without negative impacts on production. The Practical Farmers of Iowa as well as many academic researchers in the United States have made similar conclusions. Despite these findings, the percentage of coated corn seed continues to increase and is now estimated at over 90%, while soybean is over 50% in the United States. Seed companies can be owned by the same company that produces the neonicotinoids, so promoting their use is good for business. The cost to the farmer may be as much as $20 an acre for the coating. Some companies coat their GMO (Genetically Modified Organism) seed to provide traits such as herbicide resistance that can interest growers. Flea and tick treatments for pets can contain neonicotinoids and may also be marketed by the same company that produces the chemicals.
As an informed public, we all need to question the value of these pesticides that are increasing in our water systems and contributing to the decline of insects and wildlife, in some cases for use in a prophylactic manner. We need to consider alternatives to situations where there may be a real need and consider stringent laws to protect the environment and human health for the long term.
— Sally Leong is a retired biochemist and emeritus faculty member of the University of Wisconsin, Madison. As a new grandmother, Sally wants to ensure that safe and healthy soil and water are available to all life for generations to come. South Central Wisconsin Farmers Union is a member-driven chapter committed to enhancing the quality of life for family farmers, rural communities, and all people through educational opportunities, cooperative endeavors, and civic engagement in Rock, Green, and Lafayette Counties.
