Consuming a mixture of sugar syrup and glyphosate, the active ingredient in Monsanto’s Roundup herbicide, alters honey bees’ microbiomes, and these changes increased mortality among insects exposed to pathogenic bacteria, according to a study published yesterday (September 24) in PNAS.
Glyphosate is the most commonly used herbicide worldwide. It acts by blocking a key plant enzyme used in the production of amino acids. Researchers are divided on whether the chemical is safe to animals at the levels it is usually used as a herbicide. However, some bacteria are known to produce this enzyme, and the new study demonstrates what some researchers have suspected: glyphosate may harm animals indirectly by killing their resident microbes.
Nancy Moran of the University of Texas at Austin and colleagues found that glyphosate consumption can lower the levels of the common bee symbiont Snodgrassella alvi by up to five times in the guts of honey bees, and high levels of the herbicide thwarted growth of S. alvi in vitro. Moreover, bees were more susceptible to infection by Serratia marcescens, a bacterium commonly present at low levels in beehives, after drinking the glyphosate–sugar water cocktail: only 12 percent of the insects survived, compared with 47 percent of infected bees that had not been fed glyphosate.
Given these findings, more research is warranted to determine whether the proposed mechanism of honey bee morbidity contributes significantly to issues of colony collapse and overall rates of honey bee decline worldwide, University of Illinois bee geneticist Gene Robinson tells Science.
Moreover, the current study raises the possibility that glyphosate may alter the gut microbiome of other animals, including humans, Moran tells Science.