Bumblebees exposed to the world鈥檚 most popular type of weedkiller found it harder to learn and remember colours linked to rewards 鈥� which could undermine their ability to find food for the colony.
at the University of Turku in Finland and her colleagues investigated how glyphosate, in this case in the herbicide Roundup Gold, affected buff-tailed bumblebees (Bombus terrestris) in colour-based learning and memory tests.
Over five rounds, bees chose between different-coloured artificial flowers, five containing a sugar reward and five a bad-tasting quinine solution.
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Unexposed bees got better at finding the reward in each of the five rounds. But in bees exposed to the herbicide, learning fell to effectively zero after three rounds.
In a memory test two days later, using the same set-up but with flowers containing only water, unexposed bees performed near the level they had in the fifth round of training. Meanwhile, the bees exposed to the weedkiller seemed to choose colours at random, suggesting they had retained nothing.
The effect on memory was similar when bees were exposed to the weedkiller after the training session.
In another test, the bees had to discriminate between 10 odours, but their performance in this task wasn鈥檛 affected by the weedkiller.
鈥淧ollinators rely heavily on their visual system to be successful in their complex foraging environment, which includes unrewarding flowers that closely resemble, or even mimic, rewarding ones and inconspicuous hide-and-wait predators,鈥� says Helander. 鈥淢oreover, the survival and success of bumblebee colonies are highly dependent on the foraging success of their first brood workers.
鈥淚f this success is diminished, it will ultimately decrease the number of pollinators and thus their ability to pollinate flowering plants. That would be detrimental to both pollinator and plant populations,鈥� she says.
Recent research has found that bumblebees exposed to glyphosate can struggle to effectively . Another study demonstrated that they show while foraging, leading to residues in the pollen they collect.
The new research used lower doses than much of the previous work looking at glyphosate鈥檚 effects, representing a more realistic test of how bees might be affected in a real-world context using a small amount of a commercial product.
Commercial formulations include other chemicals to enhance the product鈥檚 impact, says Helander, and these may be even more toxic than glyphosate itself.
鈥淗erbicides can indirectly harm bees by removing flowers from the environment,鈥� says at the University of Texas at Austin. 鈥淭his new research demonstrates that glyphosate can impair bumblebee learning and memory, adding to a growing body of evidence showing that the herbicide can also have direct negative effects on pollinators.鈥�
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