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Researchers Study Tie Between Insecticides and Bee Health

“Just mentioning bees and pesticides in the same sentence is sure to get a buzz,” said Angus Catchot, an entomologist with the Mississippi State University Extension Service.

by Michigan State University
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beehiveBeekeepers often choose to place bee colonies near row crops, such as this cotton field in Lowndes County, Mississippi, because the plant blooms provide much-needed nectar during the hot summer months.Photo credit: MSU Ag CommunicationsMedia stories about bee health, agriculture practices and the role of pollinators in food production are a mixture of fact, propaganda and general misunderstanding, Catchot said.

“The plight of bees and beekeepers facing substantial losses over the past several years has motivated scientists all over the world to search for the causes,” he said. “As much as everyone wishes we could discover one simple fix or find one specific cause that could be eliminated, our research at MSU is discovering just how complex the relationship is between bees and the environment.”

Neonicotinoids: friend or foe?

One culprit suspected to be a serious threat to honeybee colonies is neonicotinoids, or neonics. In 2013, Europe banned their use for two years. The average consumer may wonder why the U.S. does not do the same, or why farmers would want to use something that might damage bees, when the pollinators seem to be in such a precarious position.

It helps to understand why neonics are important to row crop farmers in the mid-South, Catchot said.

“First, Mississippi’s major row crops -- corn, cotton and soybean -- do not require honeybees for pollination, but they are magnets for all kinds of insect pests above and below the ground,” he explained. “Neonics are used primarily as seed treatments, which means they coat the seeds and first address pests in the soil. Neonics are also systemic, which means they move through the plant as it grows from seed into seedling. But the insecticide is not permanently present in the plant.”

What research shows . . .

Catchot said the seed treatments provide protection for about 21 to 28 days after planting to give young plants a chance for survival. Unlike treatments applied after seedlings emerge, seed treatments prevent plant death or loss of vigor due to below-ground insect pests feeding on developing root tissue and provide a short-term residual effect in the plant as it emerges.

“Mid-South entomologists have conducted a lot of research on whether or not neonics are present in the nectar or pollen of our major row crops,” Catchot said. “Soybean is the crop bees prefer to forage on based on our surveys, and in soybean, we found zero occurrence of neonics in the flowers of the plant when the soybeans were planted with a neonic seed treatment.”

In cotton, they found no occurrence of neonics in the nectar and very low occurrence in the pollen.

“In corn, we did find low levels about 20 percent of the time, and they ranged from about three to six parts per billion, but they were more prevalent with chemical rates greater than what is typically used in the mid-South,” he said. “Based on our research, it does not appear very likely in our region of the country that bees are picking up neonics at any appreciable level from nectar or pollen in the major row crops we grow.”

Further research by Catchot’s group indicates 99 percent of the total amount of pesticide applied as a seed treatment in these three crops is gone before the plant produces flowers.

Why farmers use neonics . . .

Jeff Gore, an entomologist with the Mississippi Agricultural and Forestry Experiment Station and the MSU Extension Service, said neonics likely reduce the amount of insecticide in the environment.

“Before seed treatments, producers had to apply foliar insecticides to manage early-season pests in many crops,” Gore said. “Foliar applications also killed beneficial insects, leading to even more sprays as secondary pests surged in numbers. The method of delivery has changed, from being broadcast across entire fields or applied in the seed furrow separate from the seed.”

Neonics are also less toxic than many of their predecessors.

“Insecticides in the organophosphate and carbamate classes of chemistry were derived from research on nerve poisons,” Gore said. “As a result, they were not very selective and were highly toxic to almost all organisms with a nervous system, including people. The amount of this kind of insecticide applied to an individual field was 10 times greater or more than what is applied with neonics used as seed treatments.”

Capturing dust at planting . . .

One plausible opportunity for bees to encounter neonics is at planting.

Unlike older planters, which used a gravity-flow system that scattered seed through holes in a plate at the bottom of the hopper, more modern planters use a pneumatic system. Seeds go through tubes and into the ground, allowing for more precise seed placement and lower seeding rates -- a boon to farmers in a time when seed prices are constantly increasing.

When farmers load their planters, they add talc or graphite to the hoppers containing the seed to help the seed flow through the planter and avoid clogging up the seed tubes. The friction between the seed coatings, lubricants and tubes results in a dust that is exhausted out of the planter.

Gore said it is possible that some of this dust contaminated with seed coatings could drift onto wildflowers on the edge of fields where bees might forage. It is highly unlikely the neonic residue is in the soil from the previous crop and is moving in dust to surrounding wildflowers.

“Companies are working on exhaust systems for planters that will capture this dust so it can’t escape the planters,” he said. “Others companies are working on better seed-coat polymers to prevent the treatments from coming off in the first place.”

Gore said those developments should be available in the very near future.

“It’s a very complicated topic, and everyone wants to do the right thing when it comes to pollinators, but the decisions must be made on sound science, because this class of pesticides is extremely valuable to our farmers in this region,” Gore said.