Bees are one of those species: you either love them or hate them. On the one hand, most of us are rather partial to the occasional honey-covered slice of bread made possible by the industrious insects, while on the other hand, others become rather scared when faced with their stripy appearance. Yet, the stinging insects are fundamental for much of agriculture: a third of all our food depends on bee pollination. However, bees are in danger. In recent years, beekeepers around the world have noticed that the valuable insects are vanishing at an alarming rate. One potential cause of this decline is the use of neurotoxin insecticides to protect crops. Bees ingest the toxin when consuming contaminated pollen and nectar, which damages their central nervous system and disrupts their ability to learn and form memories. And the insects’ memories are key to their frenetic lifestyle, allowing them to recall which plant species are currently blooming, where they are located, which blooms they have visited already and how to find their way home.
In order to investigate the connection between neurotoxin insecticides and memory and learning in bees, a team of researchers led by Harry Siviter from the Royal Holloway University of London, UK, began scouring the internet for any information about the impact of these toxins on bee memories. Compiling the knowledge from 23 publications, Siviter and his colleagues found that fewer bees were able to learn to associate a scent with the presence of food and retain the memory for up to 48 h after ingesting neurotoxins. This provided strong evidence that pesticide exposure has a negative effect on the insects’ learning ability and memory. And when the team addressed previous criticisms – that the doses of toxin that the bees were exposed to in the lab did not reflect the amount of toxin that they experience in the wild – the new analysis showed that even the smallest doses, which are similar to those in the wild, impaired the insects’ abilities to learn. The team also noted with concern that the bees’ abilities to learn and form new memories were severely affected by even the shortest exposures to the toxic insecticides. And it was also apparent that all groups of neurotoxic insecticide had similar impacts: they all impaired bee memory and learning.
Thanks to the wealth of previous research in this area, the European Union is instituting a near-total ban of one group of neurotoxins – known as the neonicotinoids – by the end of the year, but the others will still be in use in other parts of the world. This ‘meta’ study highlights that it is essential that we continue to monitor the environmental impact of plant protection products if we do not want to risk our land of milk and honey.