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Study focuses on bee deaths

Wednesday, February 29, 2012

There has been a "buzz" in recent years about the serious decline of honeybee populations in the United States.

Nature's pollinators have been mysteriously dying off in large numbers, posing a potential threat to the future of the food system.

According to a study from the U.S. Department of Agriculture, honeybees pollinate approximately 80 percent of the nation's flowering crops, responsible for one-third of the food Americans eat.

They are a crucial component of food production and their absence would be felt by producers, consumers and the environment.

As the United States loses roughly one-third of its honeybee hives each year, scientists are scrambling for answers as to what's causing these dramatic losses.

A group of researchers from Purdue University may have identified one of the factors that have left bees dead near agricultural fields in spring of 2010 and 2011.

The study, published in PLoS One journal this month, investigated the potentially harmful effects agricultural pesticides have on bee populations, and the routes of exposure bees have to the chemicals.

Pesticide exposure has received a great amount of attention from the scientific community in recent years, and the Purdue study has further validated the significance of the focus.

In response to reports of bee deaths at Indiana apiaries in the spring of 2010 and 2011, bees and hives from the apiaries were analyzed during a two-year period.

"We got these reports of dead bees, and initially we noticed that they all displayed symptoms of neurotoxic poisoning," Associate Professor of Entomology at Purdue University Christian Krupke said.

Krupke also co-authored the study.

The Purdue researchers sampled the dead bees to screen for a long list of pesticides, including insecticides, fungicides and herbicides.

In the dead and dying bees they collected, they consistently found thiamethoxam and clothianidin, two common neonicotinoids better known as Cruiser and Ponco.

Neonicotinoids are a class of insecticides commonly used to coat corn, soybean and other annual crop seeds prior to planting.

These compounds act on the insect nervous system, causing paralysis and ultimately, death.

Almost all of the corn seed planted in North America is coated with neonicotinoids, bringing the insecticide to more than 90 million acres on corn along in the United States.

"We started wondering how this stuff was getting from these seeds to the insects," Krupke said.

The research team first looked at soil, finding neonicotinoid insecticides more than two years after treated seed was planted in the soil.

Next, they examined dandelions, a popular source of pollen among honeybees in the spring months during planting season. The team found low levels of neonicotinoids on the dandelion heads as well.

They also found that bees collected corn pollen when it was available, and that corn pollen contained neonicotinoids.

The most concentrated sources of the toxic insecticide, however, were found in talc following use in planters.

Talc is an anti-caking agent used to lubricate treated seeds in planters to prevent the seeds from sticking together and ensure consistent planting.

In the process, it removes and adheres to some of the material used to coat seeds.

Most of this talc exits planters through exhaust fans, taking high levels of neonicotinoids from the seeds with it.

In the United States, about 5 million pounds of talc are used annually for planting corn seeds alone.

The team of researchers sampled the talc, finding concentrations of the neonicotinoids in the parts per thousand range of concentrations.

To put this in perspective, this is more than 700,000 times the contact lethal toxicity for bees.

Krupke said there really isn't a quick fix to the bee deaths associated with neonicotinoids, but there are steps that can be done to control the problem in the short term.

"When you clean out a planter, this talc material you're cleaning should be treated as a very toxic insecticide," he said.

He also suggested farmers should avoid cleaning the planters near blooming trees or flowering plants of any kind.

In the future, more extensive methods must be considered to help protect honeybees.

"There may be a way to develop a method of filtering and then disposing this talc without having it leave the planter," Krupke said.

This would require changes to existing planting technologies and the seed application process.

Krupke also questions whether insecticides must be applied to every kernel of corn.

"There's no independent data that suggests we need to treat each and every kernel, and there's not really even an option for growers who want untreated seeds," he said.

"This is an area where we need to generate more comparative data, because that would be a really good way to cut down on neonicotinoid levels."

Although the problem has become more serious in recent years, Krupke is optimistic for the future.

"I think this is a solvable problem," he said.

"I hope that by getting more people thinking about the issue and potential solutions, we can figure out a way to improve the situation for everybody."

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