SUMMARY: Glyphosate affects the care of bumblebee brood | News

KONSTANZ / ULM (dpa-AFX) – The controversial herbicide glyphosate may threaten the breeding success of bumblebees. According to a German study, the herbicide could make bumblebees less able to maintain the temperature in the nest when food is scarce. Without enough heat, brood is at risk, and with it the survival of an entire colony of wild bees, the team writes in Science.

In recent years, research has repeatedly provided evidence of how glyphosate affects honeybees (Apis mellifera) – for example, cognition or the immune system. However, little is known about the effects of the herbicide on the nearly 20,000 species of wild bees.

A team led by biologist Anja Weidenmller of the University of Konstanz has now investigated the dark bumblebee (Bombus terrestris), one of the largest and most common bumblebee species in Germany. They set up 15 bumblebee colonies in the laboratory, each of which divided the mesh into two halves: one half of the box contained pure sugar water, while the other half contained sugar water enriched with glyphosate.

As the group observed, glyphosate exposure did not kill the insects directly. However, these colonies maintained nest thermoregulation less well when the food supply was limited. For optimal brood development, the temperature in the nest must be between 28 and 35 degrees Celsius.

“Bumblebee colonies are under very much pressure to grow as fast as possible in the short term,” Weidenmller quotes in a statement from his university. If they cannot maintain the required incubation temperature, brood develops more slowly or not at all. This limits colony growth: “Only when they reach a certain colony size in a relatively short growth phase are they able to produce sexually mature colony specimens like Queens and Drones.”

Insects generate heat by tensing the flying muscles. It costs a lot of energy, therefore especially this time is closely related to the supply of food. If this was limited in the experiment, the thermoregulatory ability of the bumblebees was reduced by 25 percent. “They can’t keep their offspring warm for so long,” concludes Weidenmller.

For biologist Vincent Doublet at the University of Ulm, this is an important finding because temperature regulation has so far been neglected in research. “The study shows that small effects at an individual level can have large consequences for the entire colony,” says Doublet, who was not involved in the work.

How glyphosate achieves this effect is still unclear. A study in honeybees found that the herbicide alters their gut flora and makes them more susceptible to certain pathogens. “It goes without saying that glyphosate also affects the bumblebee microbiome and ensures, for example, that they are less able to utilize nutrients and thus become weaker,” speculates the biologist.

Since the weedkiller impairs the cognitive abilities of honeybees, similar effects are also possible with bumblebees: “They may just not notice that the temperature in the nest is dropping.” Ultimately, various mechanisms may also interact.

The study shows Doublet that herbicides do not necessarily have to be directly fatal to insects to have dramatic consequences. Until now, approval of such measures has often been based on experimentation with well-fed honeybees living under the best conditions. In this way, complex interactions of various stress factors such as food supply, weather and pathogens are not recorded.

Lead author Weidenmller points out: “The combination of resource scarcity in cleared farm landscapes and pesticides can be a huge problem for the reproduction of bee colonies.” The new pesticides would need to be further investigated before they could be approved. So far, it has only been checked how many animals have died within 24 or 48 hours after feeding or contact with the substance: “Sub-lethal effects, i.e. effects on non-lethal organisms but differing e.g. in the physiology or behavior of animals be noticeable, may have significant negative effects and should be taken into account in future authorizations of plant protection products. “

Since last September, the use of the herbicide glyphosate in Germany has been restricted. A complete national ban on glyphosate is not possible under European law as the active substance is approved throughout the EU by the end of 2022. Plant protection products containing glyphosate should be approved with a transition period until December 31, 2023, according to the Federal Ministry of Agriculture.

Glyphosate was developed by the American company Monsanto. Since 2018, it belongs to the Bayer./fm/DP/mis chemical-pharmaceutical group

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