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New research has found that the most widely used weed killer in the world damages beneficial bacteria in the bees' intestines and makes them more vulnerable to deadly infections.
Previous studies have shown that pesticides such as neonicotinoids are harmful to bees, whose pollination is vital for about three quarters of all food crops. Glyphosate, manufactured by Monsanto, targets an enzyme that is found only in plants and bacteria.
However, the new study shows that glyphosate damages the microbiota that bees need to grow and fight against pathogens. The results show that glyphosate, the most widely used agricultural chemical to date, could contribute to the worldwide decline of bees, as well as to habitat loss.
"We have demonstrated that the abundance of dominant species of gut microbiota decreases in bees exposed to glyphosate at concentrations documented in the environment," said Erick Motta and colleagues at the University of Texas in Austin. They found that young worker bees exposed to glyphosate exposure died more often when they were subsequently exposed to a common bacterium.
Other research, from China and published in July, showed that honey bee larvae grew more slowly and died more often when exposed to glyphosate. An earlier study, conducted in 2015, showed that exposure of adult bees to the herbicide at levels found in the fields "compromises the cognitive abilities necessary for a successful return to the hive".
"The greatest impact of glyphosate on bees is the destruction of the wildflowers they depend on," said Matt Sharlow, of the Buglife Conservation Group. "Evidence so far suggests that direct toxicity to bees is quite low, however the new study clearly demonstrates that the use of pesticides can have significant unintended consequences."
Professor Dave Goulson, from the University of Sussex, said: "It seems now that we need to add glyphosate to the list of problems that bees face. This study is also further evidence that large-scale application of large quantities of pesticides has negative consequences that are often difficult to predict. "
However, Oliver Jones, a chemist at RMIT University in Melbourne, Australia, said, "In my opinion, the doses of glyphosate used were rather high. The paper only shows that glyphosate can potentially interfere with bacteria in the bee gut, not that it actually does so in the environment.
A spokesman for Monsanto said, "The claims that glyphosate has a negative impact on bees are just not true. No large-scale studies have found a link between glyphosate and the decline in the bee population. More than 40 years of solid and independent scientific evidence show that this poses no unreasonable risk to humans, animals and the environment in general.
The new research, published in the Proceedings of the National Academy of Sciences, has shown that some of the key beneficial bacteria in the intestines of bees have the enzyme targeted by glyphosate. Exposure to glyphosate also affected the ability of new worker bees to develop a normal intestinal biome.
Glyphosate exposure to intestinal bacteria has also been demonstrated in a pilot study in rats. "Intestinal bacteria play a vital role in maintaining good health, in organisms as diverse as bees and humans," said Goulson. "The discovery that these bacteria are sensitive to the most used pesticide in the world is therefore worrying."
People are widely known to consume glyphosate residues in foods – such as breakfast cereals for children – but the health impact is controversial. In August, a US court sentenced Monsanto to pay $ 289 million in damages after a jury decided that the weed killer had caused the cancer of a terminally ill man. The company filed documents to dismiss the case on September 19.
The weedkiller, sold under the name of Roundup, won a five-year lease in the EU in 2017. In 2015, the International Agency for the Fight against Cancer, IARC, declared that glyphosate was "probably carcinogenic for the man. conclusions. Monsanto insists that glyphosate is safe.
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