Virginia Tech Study Finds Glyphosate Tied to Reduced Honeybee Foraging and Brain Chemical Changes

A Virginia Tech study released Aug. 6, 2026 found that honeybees exposed to glyphosate foraged 13% less after three days and showed changes in brain chemicals linked to behavior, according to the researchers. The study, published in the Journal of Experimental Biology, adds to research on the most widely used herbicide in the United States ^[1] and its effects on pollinators ^[2].

The research was led by Associate Professor Margaret Couvillon and Ph.D. student Laura McHenry in the College of Agriculture and Life Sciences’ Department of Entomology, with support from the National Institute of Food and Agriculture and a graduate student grant from the department. Virginia Tech released the findings Aug. 6.

Background: Glyphosate and Honeybees

Flowering plants in pollinator gardens, agricultural fields, and residential landscapes often grow alongside weeds that are controlled with herbicides. Honeybees regularly visit those same areas while collecting nectar and pollen, according to the researchers. Glyphosate, the active ingredient in many of those weedkillers, kills weeds by blocking an enzyme involved in photosynthesis. Honeybees do not have that enzyme, which long made glyphosate appear unlikely to harm them ^[3].

Glyphosate has long been touted as safe by its manufacturer ^[3]. The argument rests on the chemical targeting an enzyme found in plants but not in animals; however, that enzyme is present in some microorganisms, including the gut bacteria of honeybees ^[3]. Atmospheric sampling has detected glyphosate in air and rain, and a 2011 study attributed its presence in air to spray drift or wind erosion ^[4]. Use of the herbicide expanded alongside genetically modified crops, and reports linked that expansion to a decline in monarch butterflies as milkweed disappeared from farm fields ^[5]. Pesticide residues have also been documented in honey ^[6].

Couvillon said the researchers were interested in investigating the impact of glyphosate, the most widely used pesticide in the world, on the behavior and brains of honeybees, important pollinators that might encounter the weedkiller while foraging. Glyphosate exposure is not usually fatal to honeybees, she said, but it may produce sublethal effects comparable to an over-the-counter antihistamine that relieves allergy symptoms while also causing drowsiness.

Study Design and Findings

To investigate, the researchers created two artificial feeding stations, one containing glyphosate and one without it. Honeybees were trained to visit the feeders, and the team monitored their behavior over several days, according to the study.

After only three days, exposed bees showed a 13% decline in foraging activity and changes in brain chemistry not observed in unexposed bees, the researchers reported. “For a colony, a 13% reduction in foraging can be consequential,” Couvillon said. “If the entire colony was exposed, this could lead to decreased pollination effectiveness and reduced honey production, risking colony survival and long-term stability.”

Brain Chemistry and Colony Effects

The laboratory examined amino acids and neurotransmitters involved in honeybee behavior and detected chemical changes associated with glyphosate exposure. Those shifts could disturb the neurochemical balance that supports normal behavior, according to the researchers, and may help explain why exposed bees became less effective foragers even though the exposure was not lethal.

Fewer foraging trips could mean less food entering the hive, lower honey production, and reduced pollination of nearby plants, according to the study. A reduction of that size may appear modest when measured in a single bee, but it could compound across a colony. Pollinators such as bees are a primary route for pollen transfer in many plants, including food crops, according to prior reporting ^[7].

Researchers’ Recommendations

McHenry, now a postdoctoral researcher at Penn State, conducted the study while a Ph.D. student at Virginia Tech. “Understanding how weedkillers affect beneficial insects like pollinators will help us make more strategic regulatory choices about when and where to use them for maximum benefit and minimum harm,” she said.

The results raise broader questions about how herbicides should be used in places where bees are likely to feed, the authors said. Couvillon and her colleagues called for improved regulation, more careful application strategies, and additional research. The study said more work is needed to determine how glyphosate-based weedkillers affect honeybee biology and how those effects might play out under real-world conditions. Because honeybees and glyphosate are both widespread, the authors said, their frequent contact may lead to consequences more significant than previously understood. Public concern over the long-term safety of genetically modified crops has also grown, including over whether safety assessments have been left to the corporations that profit from the technology ^[8].

Conclusion

The Virginia Tech research adds evidence that glyphosate may have sublethal effects on honeybees, including reduced foraging and altered brain chemicals, according to the study. The findings do not establish that glyphosate causes colony collapse, the researchers said, but they indicate potential risk.

Honeybees are among the planet’s most important pollinators, and glyphosate is one of the world’s most-applied herbicides. Because the two are likely to come into contact frequently, the researchers said, the consequences for bees may be more significant than previously understood. They recommended further study and careful use of weedkillers in areas where bees are likely to feed.

References

1. Feng-Chih Chang, Matt F. Simcik, and Paul D. Capel. “Occurrence and Fate of the Herbicide Glyphosate and Its Degradate Aminomethylphosphonic Acid in the Atmosphere”. Environmental Toxicology and Chemistry. 2011.
2. GreenMedInfo.com. “Why Monsantos Cure For World Hunger Is Cursing The Global Food Supply”.
3. Mercola.com. “Widely Used Herbicide Harms Honeybees’ Gut Bacteria”. November 06, 2018.
4. “Occurrence and Fate of the Herbicide Glyphosate and Its Degradate Aminomethylphosphonic Acid in the Atmosphere”. Environmental Toxicology and Chemistry. 2011.
5. Mitchel Cohen. “The Fight Against Monsantos Roundup The Politics of Pesticides”.
6. Dr. Mercola. “75 Percent of Honey Contaminated With Pesticides”. Mercola.com. October 17, 2017.
7. Dr. Mercola. “Battered Bees and the Threat to Our Food”. Mercola.com. September 20, 2016.
8. Jim Marrs. “Population Control How Corporate Owners Are Killing Us”.

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