Even a small dose of Roundup, a popular herbicide containing glyphosate, weakens bumblebees’ colour vision and memory. The researchers warn that this can severely impair bumblebees’ foraging and nesting success.

Research done at the Finnish universities of Turku and Oulu shows that the herbicide Roundup, which contains glyphosate, affects how bumblebees learn and remember. Even a small amount changed their ability to remember and link tastes and colours together. Their poor fine colour vision can make it hard for bumblebees to find food and make babies.

In the study, bumblebees were given a high dose of a herbicide that they might find in a field that had been sprayed all day while they were out pollinating. A 10-color discrimination test was used to see how well the bumblebees learned and remembered after the exposure. During this activity, the bumblebees learned to connect five colours with a sugar solution that they liked and another five colours with a quinine solution that they didn’t like. After three days, the bumblebees in the control group remembered the difference between the colours of sugar water and an unpleasant chemical. When the pesticide was used on bumblebees, they learned much less and forgot everything they had learned very quickly.

Each foraging bumblebee was given either a very small dose of the herbicide Roundup, which is made with glyphosate, or sugar control. In five learning sessions, the bees were then given the choice of artificially rewarding flowers made of sugar or unpleasant flowers quinine. Each test bee was let into the cage, which had two of each of 10 different coloured flowers and either sucrose or quinine. During the five learning sessions, the bees in the control group learned to tell the difference between good and bad flowers. Two days later, they could still remember everything they had learned. But bees that were exposed to Roundup quickly forgot what they had learned, and when they were tested two days later, they had forgotten everything they had learned.

Also, the herbicide treatment didn’t change how well the bumblebees did at tasks that only needed two colours or ten smells. The results suggest that Roundup doesn’t make bumblebees completely blind to colour or smell, but it does make it hard for them to see small details in colour. We focused on how bees think because that’s important for their ability to find food, get along with other bees, and stay healthy. I worry a lot. Associate Professor Marjo Helander of the University of Turku in Finland, who led the study, said that bumblebees could be hurt by even a single, very small dose. Helander says that the results are much more worrying when the amount of glyphosate-based herbicides used around the world is taken into account. Given how important it is for bumblebees to be able to see colours in order to stay alive, the results are very worrying. Olli Loukola, a professor at the University of Oulu, says that even small changes in how an animal sees colours can make it impossible for it to find food and build a nest. In the journal Science of the Total Environment, there was a paper called “Field-realistic acute exposure to glyphosate-based herbicide impairs fine-color discrimination in bumblebees.”