Pesticide Exposure Causes Bumblebee Flight to Fall Short

Researchers at Imperial College London found that bees exposed to a neonicotinoid pesticide fly only a third of the distance that unexposed bees are able to achieve.
Susan Fourtané
Flight mill with bee/Danny Kenna, Imperial College London 

Flight behavior is crucial for determining how bees forage. Any reduction or alteration in normal flight performance resulting from pesticide exposure could lead to colonies going hungry, and thus pollination services can be severely impacted.

Foraging bees are essential pollinators for the crops the global population eat, and the wildflowers in the countryside, gardens, and parks. Any factor compromising bee flight performance could, therefore, impact this pollination service affecting the whole ecosystem.

"Not only could this reduce the abundance, diversity, and nutritional quality of food available to a colony affecting its development, but it could also limit the pollination service bees provide." -Dr. Richard Gill

Researchers at Imperial College London, one of the world's leading universities, published a study that reveals how exposure to a common class of neurotoxic pesticide, a neonicotinoid, reduces individual flight endurance --distance and duration-- in bumblebees.

During their research, the scientists noticed that bees exposed to the neonicotinoid imidacloprid in doses they would normally encounter in fields fly significantly shorter distances and for less time than bees not exposed, which could reduce the area in which colonies can forage for food by up to 80 percent.

How humans poison bees with pesticides 

Imidacloprid is the most well-known, highly controversial, and widely used representative of the neonicotinoid insecticides. Neonicotinoids are neuro-active insecticides chemically similar to nicotine. 

The level of toxicity of imidacloprid varies depending on the species the pesticide reaches. In spite of not being very toxic to birds and slightly toxic to fish --although this also varies with species--, imidacloprid is very toxic to honeybees and other beneficial insects.

Indirectly, the pesticide also enters the human bloodstream. Honey bees are affected by neonicotinoid residues in the nectar and pollen which bees forage on. Samples of pollen include a broad range of substances, including insecticides, fungicides, and herbicides. 

Imidacloprid has relatively low toxicity for humans, and most people are scarcely exposed to it. But it is not a healthy substance. Although you will have to consume 40 grams of pure imidacloprid for it to be lethal, it can accumulate in the organism.

How neonicotinoids work

Neonicotinoids work the same way as nicotine. They bind with niconinic acetylcholine, receptors that conduct impulses through the nervous system. Normally, acetylcholine is broken down after the impulse is conducted. But neonicotinoids are not broken down, and as a result, the nervous system will keep emitting impulses.

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This will also render the receptor useless, and as a result bees and other insects become paralyzed and die. Neonicotinoids produce their effect on the nervous systems of insects much more severely than those of mammals, which means that these insecticides are much more toxic to insects.

During the tests at Imperial College London, exposed bees seemed to enter a hyperactive-like state in which they initially flew faster than unexposed bees and therefore may have worn themselves out.

"Neonicotinoids are similar to nicotine in the way they stimulate neurons, and so a rush or hyperactive burst of activity does make sense. However, our results suggest there may be a cost to this initial rapid flight, potentially through increased energy expenditure or a lack of motivation, in the form of reduced flight endurance," said the first author of the study, Daniel Kenna, from the Department of Life Sciences at Imperial College London.

"Our findings take on an interesting parallel to the story of the Tortoise and the Hare. As the famous fable states, slow and steady wins the race. Little did Aesop know that this motto may be true for bumblebees in agricultural landscapes. Just like the Hare, being speedier does not always mean you reach your goal quicker, and in the case of bumblebees, exposure to neonicotinoids may provide a hyperactive buzz but ultimately impair individual endurance," Kenna said.

Bees' flight behavior when exposed to pesticides

Researchers at Imperial College London connected bees to a flight mill to test whether bees' flight behavior changed when exposed to pesticides. The researchers recorded how far the bees flew and for how long.

After the tests, the scientists found that bees exposed to a neonicotinoid pesticide flew only a third of the distance for a third of the time compared to unexposed bees. The video below shows a bee in a flight mill during the tests. The video was recorded by researcher Ilaria Pretelli from Imperial College London. 

The team tested the bees' flight using an experimental flight mill - a spinning apparatus with long arms connected to magnets. The bees had a small metal disc attached to their backs, which allowed the researchers to attach bees temporarily to the magnetic arm.

As the bees flew in circles, the team were able to accurately measure how far they flew and how fast under a controlled environment.

"Previous studies from our group and others have shown that bee foragers exposed to neonicotinoid pesticides bring back less food to the colony. Our study on flight performance under pesticide exposure provides a potential mechanism to explain these findings," said Dr Richard Gill, lead author of the study, and also from the Department of Life Sciences at Imperial College London.

"The negative effects of pesticide exposure on flight endurance have the potential to reduce the area that colonies can forage for food. Exposed foraging bees may find themselves unable to reach previously accessible resources, or incapable of returning to the nest following exposure to contaminated flowers," he said.   

"Not only could this reduce the abundance, diversity, and nutritional quality of food available to a colony affecting its development, but it could also limit the pollination service bees provide."

Bees dying, technology tries to regularize pollination 

In turn, the problem affecting bees' flight also affects crops. Currently, yields of many crop types are under severe threat due to lack of pollination caused by bee Colony Collapse Disorder (CCD).

The bee CCD is a phenomenon that occurs when the majority of worker bees in a colony disappear and leave behind a queen, plenty of food, and just a few nurse bees to care for the remaining immature bees and the queen.

Technology and the Internet of Things (IoT)  have found a way to come to the rescue and regularize pollination of crops. Deutsche Telecom has developed connected beehives to help boost bee numbers. The Bee Corp, NimbeLink and Verizon have been trialing LTE-M to connect beehives to smart AI-assisted platforms to improve management of honeybees. This is expected to regularize essential pollination of crops.

The bee Colony Collapse Disorder is a particularly vital element of the agricultural process which is often overlooked. Connected beehives stand to boost one-third of the world’s crop production.

Even though technology could help with pollination of crops, it can't solve the problem of humans contributing to the extermination of the remaining bees on the planet, a species already endangered. 

The Imperial College London study Pesticide Exposure Affects Flight Dynamics and Reduces Flight Endurance in Bumblebees by Daniel Kenna, Hazel Cooley, Ilaria Pretelli, Ana Ramos Rodrigues, Steve D. Gill, Richard J. Gill was published today in the journal Ecology and Evolution. 

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