It is well known that bees are suffering a serious decline in their populations worldwide. Throughout the past decade, beekeepers have been reporting annual hive losses of more than 30%, sometimes even as much as 50%. Although there are several possible contributing factors—such as habitat loss and parasites—concern has been raised that exposure to pesticides, in particular the neonicotinoid family, could be playing a significant role.

Now, a new study has confirmed that these insecticides do indeed seriously harm bees, even at levels lower than those accepted for use in agriculture. According to the research, neonicotinoids damage bumblebees’ brain cells and subsequently result in colony growth deficits. Although this doesn’t prove that these chemicals are solely to blame for the worldwide decline in bees, the researchers say that the work demonstrates beyond doubt that their consumption causes brain dysfunction and poor colony performance.

Pollinators, such as insects, birds and bats, provide essential ecosystem services. Approximately 80% of all flowering plant species are pollinated by animals, with insects being the main contributors, and they also provide us with a wide variety of food, such as fruits, nuts and vegetables. It’s estimated that insect pollinators bring in around $215 billion each year to worldwide economies, and one in every three bites of food consumed is thought to depend on pollinators, in particular bees.

Unfortunately, the world is witnessing a decline in our insect pollinators, in particular bees, which has been blamed on a variety of factors. One contentious suspect is the neonicotinoid family of insecticides, which are a relatively new type of pesticide that has rapidly become the most widely used in the world.

Neonicotinoids are systemic pesticides, meaning that they are taken up by the plant and transported to all its tissues, including the pollen and nectar. They work by causing excessive excitation of nerves, eventually leading to paralysis and death. Unfortunately, bees have a genetic vulnerability to these pesticides and are less able to detoxify them than many other insects.

The amount of neonicotinoid that ends up in the nectar and pollen consumed by bees is around 2.5 parts per billion (ppb). Although it’s known that bees are susceptible to these chemicals, there has been a lot of debate over whether this amount is enough to harm them. To find out more, UK researchers fed bumblebees several different neonicotinoids at this level and investigated the effect on their brains.

As described in The FASEB Journal, they found that some neonicotinoids rapidly shut down the energy-making factories in the bees’ brain cells, the mitochondria. At even lower than 2.5 ppb, the brain cells became overly sensitive to a normally innocuous level of one of the main neurotransmitters in the nervous system. This causes brain cells to begin to malfunction, which can affect the bee’s ability to learn and form important memories, such as their route home.

To investigate whether this could be affecting colonies as well as individual bees, the researchers exposed nests in the wild once again to 2.5 ppb. Compared with untreated colonies, those exposed to neonicotinoid showed significant reductions in nest size, condition and number of bees. Although this finding contrasts with studies conducted by the industry, previous work has been the subject of criticism due to poor study design and small sample sizes.

[Via University of St Andrews, FASEB]