What are the effects of agrochemicals on the ongoing global decline of insects? Biologists at the University of Konstanz found that poor learning was impaired in bumblebees exposed to glyphosate. Their study was published in the journal General Environmental Science.
“With the global decline of insects continuing at alarming rates, we need to carefully examine the contribution of agrochemicals, beyond evaluating the death rate,” says Morgane Nouvian, biologist and fellow at the Zukunftskolleg (Institute for Advanced Studies for early career researchers) at the University of Konstanz.
With Anja Weidenmüller and James J. Foster he investigated the effect of long-term exposure to glyphosate on locomotion, phototaxis—which is movement in response to light—and learning abilities in bumblebees. For researchers, non-lethal health effects are just as important to insect conservation as lethal ones, as they reduce an individual’s chances of reproduction and survival.
A year later, Weidenmüller discovered that the collective thermal behavior of bumblebee colonies constantly exposed to glyphosate is affected when resources are scarce. In studying their ability to regulate the temperature of their brood, he found that these bumblebees could not keep their brood warm for long. And he warns that if they can’t maintain the required chick temperature, their chicks will develop more slowly, or not at all.
Absence of aversive learning
In their current study, biologists tested more than 400 bumblebee workers. Konstanz scientists showed that bumblebees chronically exposed to glyphosate could not associate a possible threat (aversive stimulus) with a visual cue during a different learning task. “From what we’ve seen, they’re not learning anymore,” Nouvian said.
In contrast, a control group of bumblebees not exposed to glyphosate showed better learning abilities. “The ability to associate a noxious stimulus with particular cues is a basic requirement for survival,” Nouvian said.
“Through this adaptive behavior, the animals have a better chance of avoiding encounters with poisons, predators and parasites. This is why the impairment of learning that we have shown, due to exposure to glyphosate, can increase the mortality rate of foragers. Such depletion of workers has an obvious effect on the success of the colony, although it remains experimental,” as it remains experimental.
As for the locomotion and phototaxis experiments, exposure to glyphosate slightly reduced the walking speed of the bumblebees but as they got used to the training equipment, and left the phototactic drive unaffected. However, it has a reduced attraction to ultraviolet light compared to blue light.
In their study, the biologists warned that even a small change in UV sensitivity could have big implications for these pollinators, which could affect their navigation and their search efficiency.
Risk assessment is attempted
Glyphosate is currently approved for use in the EU until 15 December 2023, when the decision-making process of the Glyphosate Renewal Group (GRG) application for renewal should be completed according to information from the website of the European Community.
On 6 July 2023, the European Food Safety Authority (EFSA) published a press release concluding that it “did not identify any critical areas of concern in its peer review of the risk assessment of the active ingredient glyphosate in relation to the risk it poses to humans and animals or the environment.” At the same time, EFSA reported “some data gaps […] as issues that cannot be completed or outstanding issues […].”
At the end of their study, the scientists proposed their assay—the so-called yAPIS, a fully automated, high throughput apparatus—as a way to investigate the effect of agrochemicals on insects, especially pollinators, more systematically.
In particular, this method can complement the mortality rates assessments currently used to evaluate the toxicity of agrochemicals, by providing data about their potential non-lethal effects.
Morgane Nouvian et al, Glyphosate impairs poor learning in bumblebees, General Environmental Science (2023). DOI: 10.1016/j.scitotenv.2023.165527
Awarded by the University of Konstanz
Citation: Study shows glyphosate impairs learning in bumblebees (2023, July 25) retrieved on July 25, 2023 from https://phys.org/news/2023-07-glyphosate-impairs-bumblebees.html
This document is subject to copyright. Except for any fair dealing for the purpose of private study or research, no part may be reproduced without written permission. Content is provided for informational purposes only.