Killing weed killers bees

Controversial weed killer : Glyphosate causes intestinal problems for bees

In the discussion about the pesticide - or, to put it more realistically: the weed killer - glyphosate comes up with another aspect. So far, there has been little evidence that the chemical in the concentrations that are common in agricultural practice could be dangerous for animals. This was also plausible from a molecular-biological point of view, because the substance intervenes in a metabolic pathway that animals do not have at all. However, a current study with bees shows that the herbicide can affect the animals indirectly. Because many of the intestinal bacteria that bees need for their metabolism and their defense against diseases work with exactly the same enzyme pathway that glyphosate attacks.

Plant-specific effect

In the research article, which appears in the journal "PNAS", Nancy Moran and Erick Motta of the University of Texas at Austin report that doses of glyphosate, which bees can find on agricultural land, inhibit important intestinal bacteria in insects. When young workers after contact with glyphosate bacteria of the genus Serratia exposed, they showed an increased mortality rate.

Glyphosate intervenes in the metabolism of plants by preventing an indispensable step in the production of important amino acids. Since plants have to produce all of their amino acids themselves, they perish if the dose of the poison is high enough. You will then not be able to produce vital proteins. Humans and animals, on the other hand, ingest the inhibited amino acids tryptophan and phenylalanine with their food. The metabolic pathway that glyphosate attacks is also absent from them. For these reasons, the herbicide is considered to be non-toxic for humans and animals in concentrations that can still occur in food.

Other forms of damage to health, such as the promotion of cancer, have not been proven at such rather low doses. However, a California court recently sentenced the manufacturer Monsanto (now part of Bayer AG) to pay almost $ 300 million to a former gardener who believes the herbicide is the cause of his cancer. Farmers and agricultural workers in South America, for example, also frequently complain of damage, which they attribute to having been exposed to glyphosate for a long time and in high doses.

Sensitive, insensitive

Some microorganisms use the same metabolic pathway as plants to produce those amino acids. This includes the intestinal bacterium, which is important for bees Snodgrassella alvi. The Austin biologists found that these microbes were clearly sensitive to glyphosate. However, it was also noticeable that some variants (strains) were resistant to glyphosate, although the metabolic pathway was also blocked here. They apparently have an alternative, as yet unknown method for the production of the amino acids. Other bees' intestinal bacteria use other routes from the start and are insensitive to the herbicide.

The authors of the study conclude that glyphosate-induced "disturbances in the intestinal communities can be a factor that makes bees susceptible to environmental stressors such as poor nutrition and pathogens".

Glyphosate, sold as an active ingredient in the “Roundup” product, is the most important herbicide of all. Since it also damages crops, it is usually applied in conventional agriculture before sowing. It takes a few weeks until it is sufficiently degraded. It can also be used without this restriction on areas where genetically modified plants grow that are insensitive to glyphosate.

Indirect effect

Glyphosate has completely or partially replaced predecessor substances such as alachlor and cyanazine, which have undisputed negative health effects on animals and humans. It is unclear how significant the new findings on glyphosate are.

A few years ago, the Danish biologist Charlotte Katholm had shown that glyphosate affects bacteria isolated from bees' intestines in laboratory tests. Julia Jones, an expert on the intestinal flora of bees at Uppsala University, says that an influence of this herbicide on colonization with intestinal bacteria has already been observed. For the first time, however, the new study clearly shows the connection between a herbicide, its effect on the intestinal bacteria of bees, and a pathogen. "It will be important now to understand what other herbicides and pesticides are problematic for the microbial communities in the bee intestine and how they relate," says Jones. One also needs to find out how combinations of environmental factors affect the health of bees and the health of other pollinators.

Orientation problems

Vincent Doublet, until recently at the German Center for Integrative Biodiversity Research in Halle, says that research now needs to be carried out into the broader meaning of glyphosate: "It has also been observed that bees that have been exposed to glyphosate do not find their way back to the hive well, and you have to ask yourself whether that has something to do with the intestinal bacteria, ”says the biologist from the University of Exeter. Overall, the influence of intestinal bacteria on insects is certainly significant and complex. And in addition to honey bees, bumblebees and solitary wild bees, which are also important pollinators, are likely to react to the herbicide via their intestinal bacteria. But also completely different phenomena are possibly much more strongly determined by these beneficial bacteria in the intestine than previously known: "In fact, studies have shown that some types of bacteria can protect insects against toxins". It is possible that some insect pests are not resistant to insecticides because of mutations in their own genes, but because of such microbial helpers.

Diverse influence of microbes

The Federal Institute for Risk Assessment did not want to comment on possible implications when asked. A spokesman pointed out studies on ruminants. Glyphosate would not have had any influence on their rumen bacteria, at least in the laboratory. When asked, the Federal Environment Agency (UBA) pointed out that the "ecotoxicological studies required in the course of the environmental risk assessment of pesticides" of bees and other invertebrates did not take into account the composition of their intestinal bacterial communities. A spokesman for the UBA said at the moment whether effects "would occur at all here at environmentally relevant concentrations and whether these effects occur on a scale relevant for the assessment".

It is very unlikely that glyphosate residues will negatively affect the human intestinal flora. The reason for this assumption is, among other things, that in the human intestine there are usually enough amino acids available to the bacteria from the breakdown of food.

The importance of bacteria in the intestines, but also on the skin and mucous membranes of animals and humans, seems to be very great overall. Termites, for example, would not be able to break down their food at all without special bacteria. The same applies to ruminants and horses. Even in humans, a large part of the plant food can only be used by intestinal bacteria. In addition, the microorganisms also influence the development of the immune system and deliver, directly or indirectly, messenger substances that seem to affect almost all important life processes, from susceptibility to cancer and vascular diseases to the psyche.

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