Bumblebees have had a mixed 2022 so far. Despite their success in being declared fish by the US Supreme Court, it has also been discovered that they are capable of feeling pain. Now the results of a new study found that a common pesticide can even affect their fine-color vision and long-term memory.
Glyphosate-based herbicides are the most commonly used type of pesticide in the world. However, more than 80 percent of flowering plant species and 35 percent of the world’s most important crops rely on pollinators including bumblebees. Glyphosate has already been found to negatively affect the temperature regulation in bee colonies and now scientists are looking at the effect on bumblebee vision.
In the experiment, the bumblebees (Bombus terrestris) were exposed to Roundup, a herbicide containing glyphosate. To test the effects of the herbicide on bee cognition and memory, they were presented with a 10-color discrimination task. A total of 20 artificial flowers were present with two flowers of each color. Five of those colors were positively associated with a sweet sugary treat and the other five colors were associated with a quinine-based solution that the bees do not like.
Over a period of five learning bouts, the control group quickly learned which colors were associated with the sugar reward and which were not, and were even able to remember the color combinations after three days. By contrast, the group of bees exposed to Roundup prior to the task struggled to learn the colors of the reward flowers and forgot everything they had learned two days later.
“We focused on the cognitive traits of the bees because these traits determine the successful foraging and social behavior of social insects and therefore their fitness. I am really worried. Even one very small acute dose had a harmful effect on the bumblebees,” said Associate Professor Marjo Helander from the University of Turku in a statement.
The researchers also conducted a simpler two-color task and a 10-type odor challenge and found that the bees remained unaffected. This suggests that while exposure to glyphosate-based herbicides does not make the bees completely color-blind or affect their sense of smell it does affect their fine-color discrimination and long-term memory. This lack of fine-color vision is hugely damaging to foraging rates, individual fitness, and bumblebee colony survival.
“The results are quite worrying considering the importance of colour vision for bumblebees. Even small disturbances in colour vision can be catastrophic in terms of foraging and nesting success," said Docent Olli Loukola from the University of Oulu.
The paper is published in Science of The Total Environment.