Glyphosate may not kill a honey bee outright. But research is raising a different question: what happens to the bee that survives exposure and carries on foraging?
Updated August 2026: This article was originally published in May 2025 as Glyphosate Is Messing with Bee Brains — And It Doesn’t Take Much. It has been substantially revised and expanded to include additional research into glyphosate exposure, honey-bee foraging behaviour and brain neurochemistry.
When we talk about pesticides and bees, the most obvious question is often the simplest one:
Does it kill them?
For glyphosate, the answer has helped shape perceptions of the herbicide for decades. Glyphosate has relatively low acute toxicity to honey bees compared with insecticides designed specifically to kill insects. Bees also lack the shikimate pathway — the biological pathway glyphosate targets in plants.
But perhaps “Does it kill them?” is the wrong question.
A growing body of research is examining what happens when bees encounter glyphosate at doses that don’t kill them. Researchers have reported effects involving learning, memory, navigation, immune function and other aspects of bee biology.
Two studies looking inside the heads of honey bees — using very different experiments — add another dimension.
One found that glyphosate contact altered gene expression in Africanized honey bees.
Another found that honey bees exposed to glyphosate through a food source made 13.4% fewer foraging trips, while researchers also detected changes in the balance of important neurochemicals in their brains.
The bees were still alive.
But were they unaffected?
What Happens Inside a Bee After Glyphosate Exposure?
In a 2024 study, researchers investigated what happened to gene expression in the heads of Africanized honey bees (Apis mellifera) following direct contact with glyphosate.
They collected 180 marked, 21-day-old bees and divided them into three groups: a lethal-dose group, a sublethal-dose group and an untreated control group.
The sublethal dose was 2.5573 micrograms of glyphosate per bee. The lethal treatment was 100 times higher at 255.73 micrograms per bee.
Researchers then analysed gene expression after one hour and again after four hours.
What they found was striking.
After one hour, 57 genes showed differential expression compared with controls. The researchers reported that these changes involved processes including signalling, communication and metabolism.
After four hours, 38 genes were differentially expressed, with many associated with immune response.
Perhaps surprisingly, the sublethal treatment produced more differentially expressed genes than the lethal treatment at the one-hour measurement: 53 compared with 11.
That doesn’t mean a lower dose was necessarily “more toxic”. Gene expression is complex, and the number of genes responding is not itself a measure of toxicity.
But it does demonstrate something important.
Not killing the bee did not mean nothing was happening inside it.
Changing Gene Expression Is Not the Same as Changing DNA
There is an important distinction here.
The researchers did not show that glyphosate was rewriting the bees’ DNA or causing genetic mutations.
They measured gene expression.
Genes contain biological instructions, but cells continually regulate which genes are switched up or down in response to what is happening around them. Changes in gene expression can therefore alter biological processes without changing the underlying DNA sequence.
That is what makes these findings interesting.
The bees survived the sublethal exposure, yet their biological response to that exposure could be detected at the molecular level.
The researchers concluded that glyphosate exposure altered the expression of genes associated with processes involving behaviour, metabolism and immune response.
But another study asked a different question.
Rather than looking only at what was happening inside the bee, researchers wanted to know whether glyphosate exposure might change what the bee actually did.
Glyphosate-Exposed Bees Foraged 13.4% Less
A 2025 study published in the Journal of Experimental Biology examined honey-bee foraging behaviour following sublethal glyphosate exposure.
Researchers at Virginia Tech trained honey bees to visit artificial feeding stations.
One group received ordinary sucrose solution. Another received the same sucrose solution containing glyphosate at 5 mg acid equivalent per litre.
The researchers described this concentration as field-realistic. It was selected partly because it falls within the range of glyphosate residues previously measured in bee-collected nectar several days after glyphosate had been applied at maximum label rates.
The bees weren’t confined to laboratory cages. They were trained foragers flying freely between their colony and artificial feeders.
Researchers recorded every feeding visit over a three-hour experimental period.
The result?
Bees collecting the glyphosate-containing solution foraged 13.4% less than control bees.
The difference was statistically significant.
That might not sound dramatic when we’re talking about one bee making a few fewer trips.
But honey-bee colonies depend on thousands of individual workers repeatedly leaving the hive to collect nectar and pollen.
And that raises an obvious question:
What happens if a substantial proportion of a colony’s foraging workforce begins bringing home less food?
The study did not answer that question. It did not demonstrate reduced honey production, colony collapse or impaired pollination at colony level.
Those would require further research.
But it did demonstrate something more fundamental.
Exposure that didn’t kill the bees changed their foraging behaviour.
Then Researchers Looked Inside Their Brains
The Virginia Tech researchers went further.
After the experimental exposure and two subsequent days of behavioural observations, researchers collected a subset of the bees on Day 3 and analysed several substances involved in brain signalling: octopamine, tyramine and dopamine, along with their amino-acid precursor, tyrosine.
These biogenic amines play important roles in insect behaviour.
Octopamine, for example, is involved in processes associated with learning, memory, responsiveness to food and foraging behaviour. Tyramine is both a neurotransmitter itself and a precursor to octopamine. Dopamine also plays roles in motivation and behaviour.
The findings were nuanced.
The researchers did not simply find that glyphosate universally raised or lowered all these brain chemicals.
Instead, they found an interaction between glyphosate treatment and the number of feeder visits. Among bees that made sufficiently large numbers of visits during the experimental period, brain tyramine levels increased more with each additional visit in glyphosate-exposed bees than in controls.
They also found relationships between octopamine and its precursors tyrosine and tyramine in glyphosate-exposed bees that were not apparent in control bees.
The researchers described the overall effects on bee behaviour and physiology as subtle but significant.
And that may be precisely the point.
Not Everything Changed
There is another important part of the study that shouldn’t be overlooked.
The researchers examined several behaviours besides foraging frequency.
They looked at whether bees continued returning to a previously rewarding feeder and at aspects of the famous honey-bee waggle dance used to recruit other bees to food sources.
They did not find a significant glyphosate effect on those measures.
There was also a limitation involving the waggle-dance analysis: video from two of the three experimental colonies was not good enough to reliably identify individual bees, leaving researchers with recruitment data from only one colony.
So this wasn’t an experiment in which everything researchers measured changed after glyphosate exposure.
It was more specific than that.
The clearest behavioural finding was that exposed bees foraged less.
And the brain analysis provided evidence that glyphosate exposure was associated with changes in neurochemical relationships that could help researchers investigate why.
Glyphosate Doesn’t Need to Kill a Bee to Matter
This brings us back to the problem with judging effects on pollinators primarily through mortality.
A bee can survive pesticide exposure and still potentially be affected in ways that matter.
Can it navigate properly?
Can it learn and remember where food is?
Does it respond normally to nectar?
Does it communicate normally with other bees?
Does it forage as frequently?
Does its immune system respond differently?
And what happens when these small effects are multiplied across thousands of bees in a colony?
The Virginia Tech study wasn’t starting from scratch. Its authors pointed to earlier research associating sublethal glyphosate exposure with altered sucrose responsiveness, impaired associative learning and memory, reduced navigational ability, altered sleep patterns, immune dysregulation and other physiological effects.
No single experiment answers the entire question.
But collectively, they challenge a remarkably persistent assumption:
If the bee doesn’t die, the chemical hasn’t harmed it.
What About Real-World Exposure?
This is where caution matters.
Neither of these studies proves that honey bees flying around New Zealand are experiencing these particular biological effects.
The 2024 study used controlled topical doses of glyphosate.
The 2025 experiment used an artificial sucrose feeder containing 5 mg acid equivalent per litre.
Laboratory and semi-field experiments allow researchers to isolate an exposure and observe its effects. Real landscapes are considerably more complicated.
The concentration a bee encounters will depend on where glyphosate is used, how much is applied, how recently it was sprayed, what plants are flowering, weather conditions, the bee’s foraging range and numerous other factors.
But exposure itself isn’t hypothetical.
Bees forage across agricultural land, orchards, roadsides, parks, gardens and other places where glyphosate-based herbicides may be used.
And glyphosate residues have repeatedly been detected in honey.
We Have Found Glyphosate in New Zealand Honey
This question is particularly relevant to No More Glyphosate NZ because we have been independently testing New Zealand honey.
Our testing has detected glyphosate in a number of honey samples, including mānuka and clover honeys.
Finding glyphosate in honey does not tell us what concentration individual bees encountered while foraging, nor does it demonstrate that New Zealand bees experienced the behavioural or neurochemical effects observed in these studies.
But it does tell us something important.
Somewhere between the environment, the foraging bee and the finished jar of honey, glyphosate entered the system.
Which leads to a question we think deserves considerably more attention:
If glyphosate is reaching the honey, what are the bees encountering before it gets there?
The Bigger Question for Pollinator Protection
Honey bees don’t operate as isolated individuals.
A colony functions because thousands of bees collectively perform highly specialised jobs — nursing larvae, maintaining the hive, communicating information and repeatedly travelling through the surrounding landscape in search of food.
A small change in one bee may mean very little.
A small change affecting many bees repeatedly could mean considerably more.
That is why research into sublethal pesticide effects matters.
Regulatory toxicology has traditionally placed considerable emphasis on whether a pesticide kills an organism at a particular dose. Mortality is important. But survival alone doesn’t tell us whether an animal is functioning normally.
For a pollinator, functioning normally means considerably more than simply remaining alive.
It means finding flowers.
Remembering where they are.
Returning to the hive.
Communicating that information.
And going back out again.
So, What Might It Be Doing to Us?
There is one question from the original version of this article that we think is still worth asking:
If glyphosate can alter gene expression in the tiny head of a bee after sublethal exposure, what might it be doing to us?
The bee research cannot answer that question.
Bees are not humans, their biology is different from ours, and findings from a bee experiment cannot simply be extrapolated to human health.
But that doesn’t make the question invalid.
It makes it a question requiring its own evidence.
And perhaps that’s the larger lesson from the bee research.
For decades, much of the reassurance surrounding glyphosate has rested on what it supposedly doesn’t do. Bees don’t possess glyphosate’s target pathway. Glyphosate isn’t an insecticide. Exposure doesn’t necessarily kill them.
Yet researchers continue to find biological effects outside that simple model.
Gene expression.
Brain chemistry.
Learning and navigation in earlier studies.
And now, measurable changes in foraging behaviour.
The question therefore isn’t simply whether a bee survives contact with glyphosate.
It’s whether that bee is still functioning as it should.
Because for a honey bee — and ultimately for the colony and the ecosystems depending upon it — being alive and being unaffected are not necessarily the same thing.
Resources & References:
If we want to protect pollinators, we have to start looking beyond visible harm. The following studies and articles offer deeper insight into what glyphosate is really doing—not just to the landscape, but to the very biology of bees.
Sublethal glyphosate exposure reduces honey bee foraging and alters the balance of biogenic amines in the brain.
The researchers found that bees exposed to glyphosate at 5 mg acid equivalent/L made 13.4% fewer foraging trips than controls and identified changes in relationships among brain biogenic amines.
Full study: Journal of Experimental Biology
Glyphosate contact alters the expression of genes in the head of Africanized Apis mellifera bees
This study investigates the effects of glyphosate exposure on the gene expression in the heads of Africanized honey bees (Apis mellifera). Bees were exposed to both lethal and sublethal doses of glyphosate through contact, and their gene expression profiles were analyzed after one and four hours. The results revealed significant alterations in gene expression, particularly in genes associated with neural function, immune response, and metabolism. These findings suggest that even brief contact with glyphosate can disrupt critical biological processes in honey bees, potentially impacting their health and the broader ecosystem services they provide.
Full Text: Observatório de la Economía Latinoamericana
Bee declines driven by combined stress from parasites, pesticides, and lack of flowers
This comprehensive review highlights that bee populations are declining due to a combination of stressors: exposure to pesticides, parasitic infections, and the loss of floral resources. The authors emphasize that these factors often interact synergistically, exacerbating their individual effects. For instance, pesticide exposure can impair bees’ immune systems, making them more susceptible to parasites. The study underscores the need for integrated approaches to mitigate these stressors and protect pollinator health.
PubMed Link: https://pubmed.ncbi.nlm.nih.gov/25721506/
Related articles on nomoreglyphosate.nz
Glyphosate-Based Weedkillers Harm Bee Fertility, Study Finds
A 2025 study found that exposure to a glyphosate-based herbicide reduced the proportion of living sperm in male bumblebees without significantly affecting survival — another example of why simply asking whether exposure kills a bee may miss important sublethal effects.
Read the article
How Does Glyphosate End Up in Honey Without Killing the Bees?
If glyphosate residues are reaching honey, how are they getting there while the colonies remain alive? We look at how bees can encounter glyphosate in the landscape, carry residues back to the hive, and experience exposure that may be too low to cause immediate death.
Read the article
Even the Beekeepers Know: Glyphosate Is Everywhere
New Zealand honey is promoted as natural, pure and health-giving — yet our independent testing has repeatedly detected glyphosate residues. This article examines the uncomfortable contradiction between honey’s healthy image and contamination originating in the wider environment.
Read the article
Where Have All the Pollinators Gone?
This article explores the troubling decline in bee and pollinator populations across New Zealand and the world. It highlights the role of glyphosate-based herbicides in habitat destruction, direct toxicity, and weakened ecosystems—and asks whether our chemical habits are pushing nature’s essential workers to the brink.
Read the article
Why Raising MRLs Threatens Public Health
With MPI proposing higher glyphosate residue limits on food crops, this article breaks down what MRLs really mean—and why raising them could put everyday New Zealanders at greater risk. It questions the science behind these limits and asks whether our regulators are protecting health or just aligning with industry convenience.
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Further reading:
The following books are linked to Amazon.com for your convenience. If you decide to purchase through these links, we may earn a small commission — at no extra cost to you.
Toxic Legacy: How the Weedkiller Glyphosate Is Destroying Our Health and the Environment
In her book Toxic Legacy, Dr. Stephanie Seneff presents a comprehensive review of glyphosate’s potential health impacts, arguing that its widespread use is linked to numerous chronic diseases, including autism. She emphasizes the need for a reevaluation of glyphosate’s safety.
Link: Toxic Legacy – Book Review
Whitewash: The Story of a Weed Killer, Cancer, and the Corruption of Science
By Carey Gillam
Investigative journalist Carey Gillam explores the history of glyphosate, its widespread use, and the controversies surrounding its safety assessments, shedding light on its potential risks to both human health and the environment.
Link: Whitewash [amazon.com]
Pollinator Protection: A Bee and Pesticide Handbook
By Kim Flottum
This handbook offers practical guidance on safeguarding pollinators from pesticide exposure, discussing the interplay between agricultural practices and bee health.
Link: Pollinator Protection [amazon.com]
Pollinators and Pollination: Nature and Society
By Jeff Ollerton
Jeff Ollerton provides an in-depth look at the vital role of pollinators in ecosystems and agriculture, discussing the challenges they face and the importance of their conservation.
Link: Pollinators and Pollination [amazon.com]
The Forgotten Pollinators
By Stephen L. Buchmann and Gary Paul Nabhan
This book highlights the essential services provided by pollinators and the threats they encounter, emphasizing the need for their protection to maintain biodiversity and food security.
Link: The Forgotten Pollinators [amazon.com]
Pollinators, Predators & Parasites: The Ecological Roles of Insects in Southern Africa
By Clarke Scholtz, Jenny Scholtz, and Hennie de Klerk
Focusing on the diverse roles of insects, this book examines their contributions to ecosystem functioning, including pollination, and the impacts of environmental changes on their populations.
Link: Pollinators, Predators & Parasites [amazon.com]
We’re only beginning to understand the true cost of glyphosate exposure. But the science is clear: if it’s changing the biology of bees, the ripple effects are already underway.
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