Pesticides can impair brain growth in baby bumblebees

The study reveals how specific parts of bumblebee brains grew abnormally when exposed to pesticides during their larval phase.

Using micro-CT scanning, scientists from the Imperial College London observed specific parts of bumblebee brains. They identified how particular elements of bumblebee brains grew abnormally when exposed to pesticides during their larval phase.

Scientists found that pesticides impair baby bee brain development when exposed. This affects their ability to perform a simple learning task as adults.

The study shows that baby bees can also feel the effects of contaminated food- making them weaker at performing tasks later in life.

Lead researcher Dr. Richard Gill, from the Department of Life Sciences at Imperial, said: “Bee colonies act as superorganisms, so when any toxins enter the colony, these have the potential to cause problems with the development of the baby bees within it.”

“Worryingly in this case, when young bees are fed on pesticide-contaminated food, this caused parts of the brain to grow less, leading to older adult bees possessing smaller and functionally impaired brains; an effect that appeared to be permanent and irreversible.”

“These findings reveal how colonies can be impacted by pesticides weeks after exposure, as their young grow into adults that may not be able to forage for food properly. Our work highlights the need for guidelines on pesticide usage to consider this route of exposure.”

For the study, the colony was provided with a nectar substitute spiked with a class of pesticides called neonicotinoids. Once the young emerged as adults from their pupae, their learning ability was tested after three days and after 12 days.

Scientists then compared the results with young from colonies that were fed no pesticides, and those that were fed pesticides only once they had emerged as an adult.

Next, scientists tested if the bees could learn to associate a smell with a food reward. Based on this testing, scientists found that bees that were fed pesticides when they were developing as larvae showed significantly impaired learning ability compared to those that were not.

Later on, brain scanning was performed on almost 100 bees from different colonies. Scientists found that those who had been exposed to pesticides also had a smaller volume of an essential part of the insect brain, known as the mushroom body.

Moreover, bees that were presented to pesticides during larval improvement, yet not as grown-ups, indicated similar learning impairment and mushroom body volume reduction when tested at both three and 12 days as an adult.

Lead author of the study Dr. Dylan Smith, who researched as part of the Science and Solutions for a Changing Planet Doctoral Training Partnership at Imperial, said: “There has been growing evidence that pesticides can build up inside bee colonies. Our study reveals the risks to individuals being reared in such an environment, and that a colony’s future workforce can be affected weeks after they are first exposed.”

“Bees’ direct exposure to pesticides through residues on flowers should not be the only consideration when determining potential harm to the colony. The amount of pesticide residue present inside colonies following exposure appears to be an important measure for assessing the impact on a colony’s health in the future.”

The study is published in the journal Proceedings of the Royal Society B.

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