The global decline in insects is now well documented. However, the reason for the dramatic decline is much less clear. A number of factors likely contribute, most of which are human-related. Habitat loss likely plays a role, pathogens, invasive species, climate change and of course the use of chemicals in agriculture.
The most widely used crop protection product worldwide is glyphosate. In a study just published in Science Journal Sciences A published team led by behavioral biologist Anja Weidenmüller from the University of Konstanz, has shown that hungry bumblebees fed glyphosate in their meager forage are less able to regulate temperature in their nests than animals not exposed to the herbicide. According to scientists, this can lead to worse brood development. In extreme cases, the bee colony can die because there are no longer offspring.
For their study, the researchers examined 15 colonies of bumblebees. Each of these colonies was divided into two halves. The animals were fed in the first half of the water with sugar, and the other half of the water was fed sugar with glyphosate at a concentration of five milligrams per liter. It was found that the pesticide had a negative effect on bees in two ways: On the one hand, bumblebees glyphosate spend less time caring for their brood. On the other hand, animals were no longer able to maintain a constant nest temperature when there was a shortage of food at the same time. In their study, the researchers showed that the animals were unable to maintain the temperature above 28°C for a quarter of the study period. They don’t know why.
Glyphosate also has a negative effect on honey bees
However, it is clear that hypothermia in the nest can be detrimental to the brood. The ideal temperature for offspring is between 28 and 35 degrees Celsius. Usually, adult animals ensure that the temperature always remains in this range by generating heat through the contraction of their muscles. If for some reason they cannot do this and the temperature drops below 28 ° C, then there is a high risk that the offspring, or at least part of them, will die.
For bumblebees, the death of the offspring in a year is especially bad. Unlike, say, bees, where the entire hive is hibernating, bumblebee colonies are only annual: only the queen hibernates. If you do not survive the cold season and there are no offspring, the colony will disappear.
“The strength of the current study also lies in the fact that it examined the effects of glyphosate doses that are comparable to those under agricultural conditions,” says Randolph Menzel, a biologist at the Free University of Berlin. If the animals died in the laboratory at a high dose, this does not prove that the same thing happens in nature, where insects may be exposed to much lower concentrations.
Glyphosate alone may not be fatal, but it can still harm pollinators
It has long been believed that glyphosate is harmless to insects and other animals because it is a herbicide and it also inhibits an enzyme found only in plants, fungi and microorganisms but not in animals. But there are now numerous indications that the agent is indirectly harming pollinators. “Glyphosate alone is not fatal,” says Axel Hochkirch, a conservation biologist at the University of Trier. However, so-called wetting agents are often added, which ensure that the herbicide is evenly distributed on the stems and leaves of plants. This combination is used, for example, in the “Roundup” product. “Scientists were recently able to demonstrate that the Roundup report leads to an exponential increase in bumblebee mortality,” Hochkirch says. While glyphosate alone is not fatal, it does have a negative effect on pollinators. “For example, it has already been shown that there are effects on learning behavior, sleep behavior, and development in honeybees.”
According to the study authors, the negative effects of glyphosate on pollinating insects have been underestimated so far. Their investigations indicate that it can also weaken animals, which are threatened from many different angles, thus contributing to the death of insects.