Glyphosate affects bumblebee care

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According to a study, the controversial herbicide glyphosate may jeopardize the breeding success of bumblebees. The herbicide can reduce the ability of ground bumblebees to maintain the temperature in the nest when food is scarce. Without enough heat, however, the brood is endangered and with it the survival of the entire wild bee colony, German researchers write in the journal Science.

In recent years, studies have repeatedly shown how glyphosate affects honeybees — on cognitive abilities or the immune system, for example. But little is known about the herbicide’s effects on the nearly 20,000 wild bee species.

The team led by biologist Anja Weidenmüller from the University of Konstanz has now examined dark ground bumblebees, one of the largest and most abundant bumblebee species in Germany. They set up 15 bumblebee colonies in the lab, each divided into two halves (pictured below) by a net: The feeder of one half contained pure sugar water, while the sugar water of the other half was laced with glyphosate.

Poorer thermoregulation in the nest
As the group noted, exposure to glyphosate did not kill the insects directly. However, these colonies were worse at maintaining nest thermoregulation when food supplies were limited. For optimal development of the brood, the temperatures in the nest should be between 28 and 35 degrees Celsius.

“Bumblebee colonies are under very high pressure to grow as quickly as possible in a short period of time,” Weidenmüller said in a statement from her university. If they cannot maintain the necessary incubation temperature, the brood will develop more slowly or not at all. This limits the growth of the colony: “Only when they reach a certain colony size in the relatively short growth phase are they able to produce the sexually mature individuals of a colony, namely queens and drones.”

The insects generate heat by tightening their flight muscles. But that costs a lot of energy, which is why this time is closely linked to the food supply. If this was limited in the experiment, the bumblebees’ ability to thermoregulate decreased by 25 percent. “They can no longer keep their offspring warm for that long,” sums up Weidenmüller.

“Small effects, big consequences for the colony”
For the biologist Vincent Doublet of the University of Ulm, this is a significant result, because the research has neglected heat regulation so far. “The research shows that small effects on an individual level can have major consequences for the entire colony,” said Doublet, who was not involved in the work.

How glyphosate achieves this effect is still unclear. A study with honeybees has shown that the herbicide alters their gut flora and makes them more susceptible to certain pathogens. “It goes without saying that glyphosate also affects the microbiome of bumblebees, for example making it more difficult for them to absorb nutrients and thus become weaker,” speculates the biologist.

Interactions are underestimated
The research shows Doublet that herbicides do not necessarily have to be directly fatal to insects to have dramatic consequences. Until now, the approval of such agents has often been based on experiments with well-fed honeybees living under the best conditions. Complex interactions of various stressors such as food supply, weather and pathogens would not be captured in this way.

Source: Krone

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