Bee Alert: Is a Controversial Herbicide Harming Honeybees?


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Recent court cases have focused on the possible effects of glyphosate, found in Monsanto’s Roundup, on humans. But researchers are now investigating whether this commonly used herbicide could also be having adverse effects on the health and behavior of honeybees.

A University of Texas study reported evidence that glyphosate disrupts microorganisms in the guts of bees.

In recent years, a number of studies have concluded that glyphosate could also be hazardous to bees. Although the herbicide does not appear as toxic to bees as some other pesticides (notably neurotoxins known as neonicotinoids), researchers have found that glyphosate may impact bees in more subtle ways — for example, impeding the growth of bee larvae, diminishing bees’ navigational skills, altering their foraging behavior, or even disrupting their gut microorganisms, known as the microbiome.

 The research is controversial because defenders of glyphosate use have long argued that it is benign in the environment. The herbicide is uniquely designed to target an enzyme that plants need to grow. That enzyme is essential to the so-called shikimate pathway, a metabolic process required for the production of certain essential amino acids and other plant compounds. However, the shikimate pathway is also used by some bacteria and other microorganisms, raising the possibility that glyphosate could have widespread and unexpected effects on a variety of natural organisms.

 In a September study in the Proceedings of the National Academy of Sciences, Nancy Moran, an evolutionary biologist and entomologist at the University of Texas, Austin, and her coworkers found evidence that glyphosate disrupts microorganisms found in bees’ guts.

 In a second study, published in 2015 in the same journal, Farina’s team used harmonic radar to track how long it took honeybees to find their way back to their hives. They found that exposure to relatively low doses of glyphosate appeared to hinder the bees’ ability to navigate back to the hive, and concluded that glyphosate “impairs the cognitive capacities needed to retrieve and integrate spatial information for a successful return.”

 In other research, scientists have found that glyphosate appears to interfere with the growth and survival of honeybee larvae. For example, in a study published last year in the Journal of Agricultural and Food Chemistry, Pingli Dai of the Institute of Apicultural Research in Beijing, China, and his colleagues found that elevated exposures to glyphosate can lower both the weight of bee larvae and the larval survival rate. This study also showed that glyphosate markedly decreased the diversity and richness of bacteria in the larvae’s intestines, indicators of reduced resilience.

 Meanwhile, Moran, at the University of Texas, says her lab has done follow-up confirmatory experiments using antibiotics to target the honeybee gut bacteria, with similar results on bee mortality as in the previous experiments. She emphasizes that these results have little to say so far about how important a factor glyphosate might be in the declines in bee populations. “We have to say that we don’t know at this point,” she says. “Our results suggest that it is worth studying further, which is what we are doing, and hope others will do also.”