The global decline in insects has now been clearly documented. What is the reason for the dramatic decline, however, is far less clear. A number of factors are likely to 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 commonly used crop protection product worldwide is glyphosate. In a study just published in Science Journal Science has appeared, a team led by behavioral biologist Anja Weidenmüller from the University of Konstanz shows that starving bumblebees that have been fed glyphosate in a meager diet are less able to regulate the temperature in their nest than animals that have not been exposed to the herbicide. According to the scientists, this could lead to the brood developing worse. In extreme cases, the bumblebee colony could even die because there are no more offspring.
For their study, the researchers examined 15 bumblebee colonies. Each of these colonies was split in half. The animals in one half were fed sugar water, and those in the other half were fed sugar water laced with glyphosate at a concentration of five milligrams per liter. It turned out that the pesticide had a negative effect on the bumblebees in two ways: On the one hand, the glyphosate bumblebees spent less time looking after their brood. On the other hand, the animals were no longer able to keep the temperature in the nest constant when there was a lack of food at the same time. In their study, the researchers demonstrated that the animals did not manage to keep the temperature above 28 degrees Celsius for a quarter of the study period. They don’t know why that is.
Glyphosate also has a negative effect on honey bees
However, it is clear that a drop in temperature in the nest can be harmful to the brood. The ideal temperature range for the offspring is between 28 and 35 degrees Celsius. Normally, the adult animals ensure that the temperature always stays in this range by generating heat through contraction of their muscles. If for some reason they don’t manage to do this and the temperature drops below 28 degrees Celsius, 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 particularly bad. Unlike bees, for example, where the entire hive hibernates, bumblebee colonies are only annual: only the queen hibernates. If it does 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 that occur under agricultural conditions,” says Randolf Menzel, a biologist at Freie Universität Berlin. If animals die in the laboratory at a high dose, that doesn’t prove that the same thing happens in nature, where the insects may be exposed to much lower concentrations.
Glyphosate alone may not be deadly, but it still harms pollinators
It has long been thought that glyphosate is harmless to insects and other animals because it is a herbicide and also blocks an enzyme found only in plants, fungi and microorganisms but not in animals. But there are now numerous indications that the agent also indirectly harms pollinators. “Glyphosate alone is not lethal,” 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 the plants. Such a mixture is used, for example, in the “Roundup” product. “Recently, scientists were able to show that Roundup causes a massive increase in mortality in bumblebees,” says Hochkirch. While glyphosate alone is not deadly, it does have a negative impact on pollinators. “For example, it has already been shown that there are effects on learning behavior, sleeping behavior and development in honey bees.”
According to the authors of the study, the negative effects of glyphosate on pollinating insects have so far been underestimated. Their investigation indicates that it could also weaken the animals, which are threatened from many different angles, and thus contribute to insect mortality.