Widely Used Herbicide Harms Honeybees’ Gut Bacteria

Written by Dr. Karen Shaw Becker

honeybee

Story at-a-glance -

  • Glyphosate, the active ingredient in Roundup herbicide and the most used weed killer worldwide, may be disturbing specialized bee gut microbiota that is necessary for proper growth and defense against pathogens
  • Bees fed glyphosate had five times less of the bacterium Snodgrassella alvi as those fed sugar syrup
  • Snodgrassella alvi bacteria exposed to glyphosate in a petri dish also stopped growing or had slowed growth
  • The change appeared to make the bees more susceptible to infections; while 47 percent of bees fed sugar syrup survived infection with a pathogenic bacterium called Serratia marcescens, only 12 percent of the glyphosate-fed bees were as fortunate

Glyphosate, the active ingredient in Roundup herbicide and the most used weed killer worldwide, has long been touted as safe for the environment by the company that makes it. A key reason behind the argument for glyphosate’s purported safety is that it targets an enzyme called 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the shikimate pathway — an enzyme found in plants but not in animals.

Animals lack the shikimate pathway, however EPSPS is found in some microorganisms, including the gut bacteria of many species, such as honeybees. Bee gut bacteria commonly contains the EPSPS enzyme targeted by glyphosate, and research published in Proceedings of the National Academy of Sciences (PNAS) suggests the chemical may be disturbing this specialized bee gut microbiota that is necessary for proper growth and defense against pathogens.1

Glyphosate May Be Harming Bees by Disturbing Their Gut Microbiota

Honeybees, as major pollinators of flowering plants, have many opportunities to come into contact with glyphosate while foraging. It’s also believed that pesticides that exist on pollen and nectar collected by bees may be stored inside their nest, affecting nest mates in varying ways.2 One way appears to be via a disturbance to the gut microbiota.

In honeybees, eight bacterial species dominate. In newly emerged worker bees, the gut bacteria aren’t acquired until the bee has a chance to interact with other worker bees in its first few days of life. It’s known that bees without normal microbiota have a number of health problems, from reduced weight gain and altered metabolism to increased risk of premature death.

For the featured study, 2,000 bees were fed either a sugar syrup or a syrup containing glyphosate at levels similar to those found in the environment. Those fed glyphosate had five times less of the bacterium Snodgrassella alvi as those fed the sugar syrup. Snodgrassella alvi bacteria exposed to glyphosate in a petri dish also stopped growing or had slowed growth.3

The change appeared to make the bees more susceptible to infections. In fact, while 47 percent of bees fed sugar syrup survived infection with a pathogenic bacterium called Serratia marcescens, only 12 percent of the glyphosate-fed bees were as fortunate. Researchers explained:4

“We found the microbiome was affected by glyphosate exposure during and after gut colonization, and that glyphosate exposure during early gut colonization increased mortality of bees exposed to an opportunistic pathogen.”

The findings were concerning enough that the researchers recommended farmers and homeowners avoid spraying glyphosate on plants that bees may frequent. Study author Erick Motta, a graduate student at The University of Texas at Austin, said, “We need better guidelines for glyphosate use, especially regarding bee exposure, because right now the guidelines assume bees are not harmed by the herbicide … Our study shows that’s not true.”5

Glyphosate Also Influences Honeybee Navigation

Beyond harming gut bacteria, glyphosate may also be causing other disturbances to honeybees, including harming their ability to navigate. When honeybees were fed a sugar solution containing traces of glyphosate (0.500 μg per animal), changes were noted in their navigation, including spending more time performing homeward flights than control bees or bees treated with lower concentrations, and also performing more indirect homing flights.

Further, after a second release, bees fed the control solution had more direct homeward flights while the glyphosate-treated bees did not. Researchers explained in the Journal of Experimental Biology:6

“These results suggest that, in honeybees, exposure to levels of GLY [glyphosate] commonly found in agricultural settings impairs the cognitive capacities needed to retrieve and integrate spatial information for a successful return to the hive. Therefore, honeybee navigation is affected by ingesting traces of the most widely used herbicide worldwide, with potential long-term negative consequences for colony foraging success.”

Bees May Be Exposed to Nearly 100 Different Pesticides

Glyphosate is only one of a number of pesticides that bees may come into contact with on a regular basis. In a study of 91 honeybee colonies owned by commercial beekeepers, researchers detected 93 different pesticides, and the more pesticides detected, the higher the risk of colony death — regardless of the pesticide doses.7 Study author Dennis vanEngelsdorp, Ph.D., an assistant professor of entomology at the University of Maryland, said in a statement:

“Our results fly in the face of one of the basic tenets of toxicology: that the dose makes the poison. We found that the number of different compounds was highly predictive of colony death, which suggests that the addition of more compounds somehow overwhelms the bees’ ability to detoxify themselves.”8

High levels of fungicides, in particular, were noted inside the hives, and while it’s often believed that fungicides (like glyphosate) is “safe” for bees, the study actually found the chemicals were linked to a higher risk of colony death. It’s becoming increasingly clear that there may be no such thing as a “safe” pesticide when it comes to protecting bees and other pollinators.

Bee Populations on the Decline

Both commercial and wild bees have been declining worldwide in recent years. There are more than 4,000 bee species native to North America and Hawaii, but only about 1,500 of them have available data to assess their numbers.

Of those, more than half are declining and nearly 1 in 4 is imperiled and at increasing risk of extinction, according to an analysis by the Center for Biological Diversity.9 “A primary driver of these declines is agricultural intensification, which includes habitat destruction and pesticide use,” the analysis explained, adding:10

“Sublethal impacts caused by pesticides include decreased fitness, reduced brood rearing and reduced female production, all of which lead to smaller populations that can eventually cause local to large-scale extinctions.”

The use of such chemicals should be seriously questioned in light of the priceless benefits bees and other pollinators bring to society. One of every three bites of food is dependent on bees for pollination, and 90 percent of wild plants also depend on insect pollination to survive. Currently, however, more than 40 percent of insect pollinators, including native bees, are highly threatened.

If you want to give them a helping hand, eliminate the use of chemical pesticides in your backyard and grow native, non-GMO plants, especially those that provide nectar and larval food for pollinators.

Click Here and be the first to comment on this article
Post your comment