Role of pesticides on honeybee health examined

Mississippi State researchers look at honeybee health effects of pesticides in field settings; herbicides also threat.

Because bees are important to the success of crops, honeybee health is important to Mississippi State University.

Jeff Gore, a Mississippi Agricultural & Forestry Experiment Station researcher at the Delta Research & Extension Center in Stoneville, Miss., participated in a recent U.S. Department of Agriculture-Agricultural Research Service study of pesticide toxicity to honeybees. The study was conducted in Stoneville at the USDA-ARS Jamie Whitten Delta States Research Center. It was part of ongoing efforts to protect the population of pollinators.

Researchers tested 42 commonly used pesticides in a realistic field setting to determine their toxicity levels for honeybees. The pesticide study examined 40 insecticides, one herbicide and one fungicide.

USDA senior investigator YuCheng Zhu and colleagues found that 26 pesticides killed nearly all bees that came into direct contact with them. However, seven pesticides — including glyphosate, which is used in Roundup and other weed control products — killed practically no bees.

“There are many chemicals that have been used in agriculture that were once thought safe for bees,” said Jeff Harris, MSU Extension Service bee specialist and Experiment Station researcher. “This study was important to determine what impact these pesticides have on honeybee health.”

Harris said the study was also important in the way it tested toxicity.

“Many times chemicals are tested for acute dermal toxicity, when different doses are touched to the body of the bee. Others look at acute oral toxicity, when the chemical is put in the bees’ food,” he said. “The big question is what happens in the environment, and this study tried to address that question.”

John Adamczyk, research leader with the USDA-ARS lab in Poplarville, Miss., said the study looked at acute toxicity, or whether these pesticides killed bees when they were exposed to realistic doses of the chemicals in an agricultural setting.

“This study gives us a baseline,” Adamczyk said. “We were looking at the acute kill, and we were able to put these chemicals in a sort of order based on toxicity.”

Adamczyk said the study produced no surprises. The chemicals tested were found to have toxicity similar to what the manufacturers and the Environmental Protection Agency stated.

The study applied chemicals as spray to mimic application methods used by farmers. They tested those commonly used in agricultural settings and simulated a situation where an adult bee in a cotton field is accidentally sprayed.

Researchers found that many — but not all — of the neonicotinoids, organophosphates and pyrethroids tested killed nearly all of the bees these chemicals touched. However, a few pesticides, including glyphosate and acetamiprid, killed practically no bees in the test.

A few chemicals were found to be more toxic than originally assumed when used at field application concentrations. One pesticide that was considered a high risk for bees was found to be only an intermediate risk when used at the labeled rate.

Adamczyk said this study that created baseline data was just the tip of the iceberg, and much more work needs to be done.

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Herbicide threat to bees

People who care about honeybees know that insecticides and pollinators are usually a bad mix, but it turns out that herbicides used to control weeds can spell even bigger trouble for bees.

"When farmers burn down weeds before spring planting, or people spray for goldenrod, asters and spring flowers, or when power companies spray their rights-of-way, they’re killing a lot of potential food sources for bees and wild pollinators," Harris said.

He said the direct effect of these chemicals on bees is so much less of an issue than their loss of food supply.

“Before we got back into bees, I sprayed pastures by the barrel to kill weeds. As a cattle farmer, weeds are a nuisance,” Johnny Thompson, vice president of the Mississippi Beekeeping Assn. and a cattle and poultry farmer, said. “I’m trying to grow grass for the cows to eat and not weeds, but as a beekeeper, those weeds are not weeds. That’s forage for the bees.”

Today, Thompson said he uses a brush mower more than he sprays herbicides to keep the food supply for bees intact on his land.

“If you kill everything the bee has for food, you may as well go in and spray the hive directly. The bees are going to die,” he said. “All the emphasis is being put on insecticide, but the greater risk to bees are the herbicides.”

Thompson has made management changes for the sake of his bees’ food supply, but he recognizes the tension between current agricultural management practices and pollinators’ best interests.

Crops in the field, especially soybeans, are great sources of bee forage, and farmers and beekeepers can coordinate to protect both of their interests.

Farmland is not the only place bees find food. Yards, roadsides, golf courses and power line rights-of-way are other places bees forage when plants are allowed to bloom naturally.

“We need to stop looking at them as weeds and instead look at these plants as forage,” Thompson said. “I can manage around the insecticides, but if herbicide use means there’s nothing for a bee to eat, there’s no reason to put a hive in an area.”

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