DNR says it will look harder at insecticides' effect on Minnesota deer

·4 min read

Nearly 2,000 hunters who signed up to participate in a pilot study to gauge the prevalence of neonicotinoids in Minnesota's deer population haven't heard the last from researchers who launched the project in 2019.

Based on this week's surprising announcement that the insecticides have infiltrated deer in just about every corner of the state, the Department of Natural Resources is on a quest to determine if the so-called "neonics" are detrimental to the health of the state's most-sought-after game animal. Discussions already have begun with wildlife officials in North Dakota to collaborate on a research paper showing dispersal of the chemicals in deer from both states. In North Dakota, 52% of deer spleens checked for neonics have tested positive.

In addition, the DNR will soon receive a deeper analysis of the neonic levels and specific types of neonics found in the deer spleens provided by Minnesota hunters.

What the DNR already knows but didn't say this week in its news release is that some whitetails in the study carried neonic concentrations greater than .33 parts per billion — the level at which fawn survival decreased in a study on captive deer in South Dakota. Phase one of the Minnesota study found neonic levels as high as 6.1 parts per billion, the DNR wrote in letters this week to the hunters who provided spleen samples.

"I can't hardly wait to see what's next,'' said Judy Hoy, a Montana wildlife rehabilitator and researcher whose early work on neonicotinoids paved the way for the deer studies in South Dakota and Minnesota.

Hoy said correlations she has long drawn between neonics and birth defects in deer, birds and other animals have been "trashed'' by other scientists. But she said she was vindicated by the national research paper that came out of the South Dakota State University Wildlife and Fisheries Captive Facility in March 2019. Researchers in that study fed neonics to captive fawns and adult female deer. Adverse effects included shortened jawbones, reduced organ weights, decreased foraging, genital abnormalities and reduced fawn survival, researchers reported.

Michelle Carstensen, DNR's wildlife health program supervisor, said some Minnesota whitetails "absolutely'' have concentrations of neonics associated in the South Dakota study with reduced fawn survival.

"We don't want to get ahead of ourselves ... we're trying to really understand what this means for deer,'' she said.

Eric Michel, a research scientist who worked on the South Dakota study before taking a job with the Minnesota DNR, said Minnesota's initial research on wild deer doesn't say anything right now about whether neonics are affecting the state's whitetail population. But the goal of continued research is to find out, he said.

Within the next month or two, a laboratory at Michigan State University will complete deeper screening of a subset of spleens already tested for neonics. In the original screening, 61% of 800 spleen samples were found to be contaminated. Now, for a cost of $100 per sample, 57 of those spleens with varying concentrations of neonics are receiving more sensitive work-ups at Michigan State. The added molecular analysis will show precise concentrations and specific types of neonics — the most widely used class of insecticides worldwide.

Carstensen said the big surprise so far is the prevalence of the chemicals in deer living far away from agricultural areas, where neonics reign as the chief pesticide in row crops. Part of the foundation for testing deer spleens was a DNR study that simulated springtime spills of crop seeds treated by neonics. Using trail cams in 2016 and 2017, researchers documented consumption of the coated seeds by 12 species of birds and 13 species of mammals. Deer were observed eating large amounts of seeds in short amounts of time and the study authors said the results called for researchers to revisit "previously held assumptions about the safety of neonicotinoid seed treatments.''

Carstensen said the initial spleen testing shows that every part of Minnesota has deer carrying the insecticides. Even in Deer Permit Area 197, a northern forested area around Leech, Cass and Winnibigoshish lakes, five of the eight spleen samples collected from hunters were found to contain neonics.

"It's from Harmony to Bovey,'' she said. "How the heck are deer everywhere getting exposed?' It's got to be something we're doing.''

The agency plans to enlist hunters again this fall in the collection of more deer spleens for continued study. The research is entirely about deer health, not human health, Carstensen said. The concentrations found in deer spleens have been far below the U.S. Environmental Protection Agency's allowable levels for consumption of other foods, like fruit or beef, that may have neonicotinoid residue.

In addition, Carstensen said the DNR still is researching and not pointing the finger at agriculture for the spread of neonics. The pesticides are found in hundreds of other products, she said, including insect control treatments for homes, gardens, yards, orchards, wineries and for pets.

Most of the focus on effects of neonicotinoids on. The pesticides were put into use starting in 1994 — highly toxic to insects. But the European Union banned all outdoor use of neonics in 2018 after a large number of scientific studies found harm to pollinators.

Tony Kennedy • 612-673-4213

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