World’s most used weedkiller may cause bee deaths globally

25 Sep 2018

Image: Austinphotog1974/Shutterstock

The world’s most widely used herbicide may be taking a toll on the health of honeybees.

Glyphosate, the active ingredient in Monsanto’s Roundup weedkiller, may be harming bees.

According to research from the University of Texas at Austin, honeybees exposed to glyphosate lose some of the beneficial bacteria in their gut. This loss leaves the insects more susceptible to infection and death from harmful bacteria.

Glyphosate interferes with a crucial enzyme found in plants and microorganisms, but not animals. It kills plants by blocking the enzyme used to make key amino acids.

Is weedkiller harming bees?

The findings were published in the journal Proceedings of the National Academy of Sciences.

Evolutionary biologist Prof Nancy Moran took approximately 2,000 bees from a hive and fed some a sugar syrup and others a syrup dosed with glyphosate. Three days after they returned to the hive, the bees who had ingested the glyphosate had lower levels of the beneficial Snodgrassella alvi bacterium than the other insects. The team found that young worker bees exposed to glyphosate died more often when they were later exposed to a common bacterium.

Researchers said some of the findings were confusing. Bees that got the most glyphosate had a more normal-appearing microbiome after three days than those with lower doses. Moran said it is not clear whether this is because more bees with the larger dose died, leaving those who better withstood the weedkiller behind.

Further tests showed bees that consumed glyphosate had five times less of the bacterium. In a petri dish, most strains of S alvi either slowed or stopped growing after a high dose of glyphosate. Moran also noted that the gut microbiome of bumblebees is similar to that of the honeybee, so they may also be affected.

Researcher Erick Motta said: “We demonstrated that the abundances of dominant gut microbiota species are decreased in bees exposed to glyphosate at concentrations documented in the environment.”

Monsanto responds

A spokesperson for Monsanto said that claims glyphosate had a negative impact on honeybees “are simply not true”. They added: “More than 40 years of robust, independent scientific evidence shows that it [glyphosate] poses no unreasonable risk for humans, animal and the environment generally.”

A chemist at RMIT University, Oliver Jones, told The Guardian that he believes the doses used in the research “were rather high” and added: “The paper shows only that glyphosate can potentially interfere with the bacteria in the bee gut, not that it actually does so in the environment.”

Moran noted that the study is not enough evidence to concretely conclude that glyphosate is having population-level impacts on honeybees. She added that there “really is a lot of [glyphosate] in both agricultural and urban areas”.

“At the moment, there are no guidelines that you should avoid spraying glyphosate on or near bees, since it’s considered completely innocuous,” she added. The researchers say rules around its use should be drafted.

Another recent study showed that bumblebees had acquired a taste for a class of pesticide known as neonicotinoids, eventually preferring food laced with the chemical to unaltered food. While the study may not be entirely conclusive, it does demonstrate that some widely used chemicals could be affecting ecosystems in ways we have not yet discovered.

Ellen Tannam was a journalist with Silicon Republic, covering all manner of business and tech subjects