Pesticide contamination may be the cause of abnormal brain development in bumblebee larvae, according to a new paper published recently. The researchers scanned the brains of 92 worker bees using microCT technology and found that the brain regions of learning-related insects did not grow properly, which could undermine the bee’s ability to serve the bee population as adults.
Bees, as pollinators, are known to make important contributions to the health of countless ecosystems, helping plants to reproduce, grow and produce food. Sadly, the number of many species is declining, in part because of human behaviour, such as spraying crops with pesticides.
Lead researcher Dr Richard Gill, of the Life Sciences Department at Imperial College London, said: “Bee colonies are superorganisms, so when any toxin enters the bee population, they can cause problems with the development of their larvae. Worryingly, in this case, when the larvae are fed with pesticide-contaminated food, this can lead to less growth in part of the brain, resulting in smaller and less functional parts of older adult bees. This appears to be a permanent and irreversible effect. “
Researchers have provided many bumblebee populations with a pesticide-contaminated nectar alternative. The researchers tested the larvae’s ability to learn by examining whether they could learn to link a smell to food rewards. When they were considered adult bees, the researchers again tested their ability to learn. At this time, bee food has been nine days without pesticide contamination.
The team then scanned the brains of 92 worker bees using a microcomputed tomography technique. Some bees were chosen because they were exposed to pesticides from the larvae stage, while others were fed pesticides after they were considered adult. The last group was completely free from exposure to hazardous substances.
The researchers found abnormal brain structures in bees exposed to pesticides. Compared to other specimens, an area of the insect brain called a “mushroom body” (related to an individual’s ability to learn) is reduced in volume. Compared to other bees, those who came into contact with pesticides from the larval stage were impaired in their ability to learn during both tests. In addition, when the larvae’s brains were scanned for a second time, the larvae did not improve – when they were not exposed to the substance for several days. This suggests that the negative effects of pesticides on brain formation may be permanent.
According to the researchers, pesticide damage may make them perform as badly as adult bees, potentially increasing the risk of bee colonies collapsing. The study’s authors say their work highlights the importance of imposing new guidelines on pesticide use.
The paper has been published in the Proceedings of the Royal Society B.