White-tailed deer spleens in MN indicate exposure to insecticides

In a 2019 Minnesota Department of Natural Resources (MDNR) Ungulate Research study, scientists found insecticides in 61 percent of whitetail deer spleens examined. This percentage has increased to 94 in a follow-up to the recently published study, based on collections made in 2021.

The insecticides MDNR is testing the state’s white-tailed deer for are called neonicotinoids, or neonics for short. They are widely used in agriculture, but are also present in about 500 registered household products, says one of the study’s authors, MDNR scientist Eric Michel. Field & Stream. While neonics are designed to target specific receptor sites in the insect’s brain, recent research shows that the chemical has an impact on non-target species as well. “That’s kind of where we come in,” says Michel. “We’re specifically looking at white-tailed deer, but other game birds and non-game birds have been shown to be affected by neonics.”

MDNR has been asking hunters across the North Star State to extract and submit the spleens of deer they harvest since 2019, and during the program’s first year, MDNR tested 799 spleens. In the most recent 2021 survey, researchers collected 496 samples.

The 2021 results came only from the southwestern part of Minnesota where farmland transitions to forest, but Michel says the issue of neonics in deer spleens isn’t exclusive to agricultural parts of the state. “We’re finding deer that have been harvested in far northeastern Minnesota that have neonic concentrations in their spleens,” he says. “We are talking about as far as the Boundary Waters area, an area that is very remote. What we are asking is, how is it going there? How are these deer being exposed?”

Biologists in Minnesota are finding more insecticides in white-tailed deer than ever before
This young hunter submitted his deer spleen to the MDNR for testing after a successful hunt. MDNR

The 2021 results reported a significant increase in the average level of neonics in the spleens of the deer examined. Using a risk threshold established in a 2019 survey of captive deer in South Dakota, the authors determined that 64 percent of samples met or exceeded the threshold in the previous year’s round.

Neonics are applied through seed treatment, foliar spray, granular distribution and tree injection. By 2008, according to the Minnesota Department of Agriculture, “neonicotinoids accounted for 80 percent of seed treatments and 24 percent of all insecticide use globally. In North America, of the 133 million acres of corn, soybeans, wheat, cotton and sorghum treated with insecticides, over 98 percent were treated with neonicotinoids.” Meanwhile, a 2020 University of Minnesota study found widespread neonics in Minnesota’s surface water.

Michell, who also worked on the South Dakota study, hopes that further research will uncover the source of neonic exposure for deer living in areas that are far from farmland. “The boundary waters are very remote,” he says. “Going back to that South Dakota study, we had some samples that came from the Badlands, and they had evidence of neonic exposure. It is not just about agriculture. There’s something bigger here.”

Read more: Ohio Town Proposes Urban Hunting to Reduce Growing Deer Population

When it comes to eating deer that may have been exposed to neonics in one way or another, Michell says hunters shouldn’t be alarmed. “We’re not concerned about human consumption of venison in relation to neonic proliferation or exposure,” he says. “We’re conducting this study purely from a deer herd health standpoint.”

MDNR will continue sampling this fall, but only in two hunting permit areas. Michel also hopes to collect more samples at different times throughout the year to better understand how seasonal neonic exposure may affect deer.

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