There is a great deal of discussion about the many chemicals used in farming and what impacts they have on both ourselves and other animals, particularly insects.
Pesticide is the broad term used for substances intended to control organisms that are considered harmful or undesirable. Within this group are insecticides, designed to target insects; herbicides, designed to control plants; and fungicides, used against fungi. Different products target different biological processes and contain different active ingredients. They can therefore have very different effects on organisms that were never intended to encounter them.
One of the most widely discussed is glyphosate, an active ingredient used in many herbicides. It is familiar to most people through products such as Roundup.
Honeybee colonies and beekeeper in a flowering oilseed rape field.
What is Glyphosate?
Glyphosate is designed to kill plants. It works by blocking an enzyme called EPSPS within the shikimate pathway, a metabolic pathway plants need to produce particular aromatic amino acids. Once this pathway is disrupted, the plant can no longer maintain normal growth and function and eventually dies.
Glyphosate is used extensively to control weeds, but its agricultural use has not been confined to spraying unwanted plants. Glyphosate-based products have also been used as pre-harvest treatments in some cropping systems, meaning that application may take place close to harvest on crops destined for the human food chain.
The Food Safety Authority of Ireland (FSAI) confirms that glyphosate-containing herbicides may be used as pre-harvest treatments. Glyphosate residues can therefore occur in food. These residues are regulated through legally established Maximum Residue Levels (MRLs). On a side note, there are currently no requirements to label foods where glyphosate-containing herbicides have been used during their production. For more information on glyphosate in food and how residues are regulated in Ireland, see the Food Safety Authority of Ireland guidance on glyphosate.
This is also an area where agricultural practice and product authorisations have changed. In Ireland, glyphosate can no longer be used specifically for harvest management or desiccation of crops. Teagasc notes, for example, that its previous use to aid the harvesting of oilseed rape is no longer permitted. However, pre-harvest application remains possible in certain circumstances for weed control. Teagasc provides further guidance on the changes to glyphosate labels and permitted pre-harvest use in Ireland.
Why would glyphosate affect a honeybee?
Honeybees do not themselves possess the shikimate pathway that glyphosate is designed to inhibit. On that basis, glyphosate has historically been considered comparatively low-risk to honeybees in terms of acute toxicity. In other words, unlike an insecticide designed to interfere directly with insect physiology, glyphosate has no obvious biological target within the honeybee itself.
And, broadly speaking, glyphosate is not highly acutely toxic to honeybees. Its reported LD50 — the dose required to kill half of the bees in a toxicity test — is greater than 100 micrograms per bee. This relatively low acute toxicity helped establish the idea that glyphosate was comparatively pollinator-friendly.
But mortality answers only one question: Did the bee die?
It does not necessarily tell us whether a living bee continues to behave and function normally.
Over recent years, research into glyphosate and honeybees has reported sublethal effects involving functions such as learning, memory, navigation, sucrose responsiveness, sleep and physiological regulation. These observations raise a more complex question about a herbicide that does not directly target bee biology:
What happens to a honeybee that survives glyphosate exposure?
Research from a team at Virginia Tech, published in the Journal of Experimental Biology in 2025, examined that question in an especially practical way — by looking at what exposed forager bees actually do.
What is sublethal glyphosate exposure?
Sublethal exposure means exposure to a substance at a level that does not kill the organism but may still alter its physiology or behaviour. This distinction is particularly important in honeybees.
A worker bee may survive exposure yet experience a change in her ability or motivation to forage, navigate, learn, communicate or respond normally to food. For a solitary animal, such behavioural changes affect only that individual (and their offspring). In a honeybee colony, however, thousands of workers collectively perform the tasks required to keep the colony functioning. Because of this, small changes in individual behaviour can therefore become biologically important when they occur repeatedly across a workforce.
How did researchers test glyphosate exposure in honeybees?
Researchers Laura McHenry, Roger Schürch, Margaret Couvillon and colleagues at Virginia Tech trained honeybee foragers from three colonies to visit artificial feeders.
The bees were divided between two feeders offering the same sucrose reward. The control group received ordinary sucrose solution. The treatment group received the same solution containing glyphosate at a concentration of 5 mg acid equivalent per litre.
This concentration was chosen carefully. According to the researchers, it falls within the range of glyphosate residues previously found in bee-collected nectar three to seven days following application at maximum label specifications. It is comparable with concentrations used in other studies of sublethal glyphosate effects.
The researchers followed 40 control bees that were not exposed to glyphosate and 46 glyphosate-exposed bees. They recorded every visit they made to the feeders during a three-hour experimental period. They also examined recruitment-related behaviour within the colony and later analysed the brains of a subset of the experimental bees.
The primary question was straightforward:
Would bees exposed to a sublethal concentration of glyphosate continue to forage at the same rate as unexposed bees?
Glyphosate-exposed honeybees foraged 13.4% less
Bees collecting the glyphosate-containing sucrose solution made approximately 13.4% fewer feeder visits than bees collecting untreated sucrose solution. The control bees averaged an estimated 31.76 feeder visits during the experimental period. Compared with 27.52 visits in the glyphosate treatment group. However, the researchers did not find a decline in all the behaviours they measured.
Glyphosate exposure did not significantly alter:
dance frequency;
the number of waggle runs within dances; or
the bees’ persistence in returning to a food source after it stopped providing a reward.
in short, the study showed that while the exposed bees were performing less feeder visits, they were still capable of returning to the feeder, entering the colony and participating in recruitment behaviour.
The researchers describe a particularly interesting possible scenario. Foragers encountering glyphosate-contaminated nectar might reduce their foraging frequency while recruitment continues normally. That could result in reduced total nectar inflow while exposure to glyphosate residues within the colony continues.
Honeybee collecting pollen from Sunflower
Why does 13.4% less foraging matter to a honeybee colony?
A honeybee colony depends on repeated individual actions, such as forager bees collecting food. A successful forager leaves the hive, travels to a food source, collects nectar or pollen, returns to the colony, unloads what she has gathered and then repeats the process. Other bees may subsequently be recruited to profitable forage through communication within the colony.
A reduction in foraging by one worker would have little measurable effect at colony level. But a colony’s foraging force consists of thousands of workers. If a similar reduction in activity occurred across a substantial number of them, the cumulative effect could mean less food entering the hive.
The scale becomes clearer when we look at pollen alone. A honeybee colony may consume between 12 and 34 kg of pollen each year, gathered through thousands upon thousands of individual foraging trips. If a substantial proportion of the colony’s foragers made fewer trips, the cumulative reduction in incoming food could become significant over the course of a season. You can read more about the importance of pollen to honeybee nutrition in our guide to pollen and honeybees.
The present experiment did not measure whole-colony honey production or demonstrate that colonies exposed to glyphosate collect precisely 13.4% less food. Those would be different questions requiring colony-level studies. What it demonstrates is more fundamental: Sublethal glyphosate exposure changed the foraging behaviour of individual honeybees.
Honeybee using its proboscis to drink liquid.
Glyphosate exposure was linked with changes in honeybee brain chemistry
The researchers then investigated whether the behavioural change was accompanied by measurable differences in the bees’ neurochemistry.
After three days, they analysed the brains of experimental bees for several biogenic amines and related compounds: octopamine, tyramine and dopamine, together with the amino acid precursor tyrosine. Biogenic amines are chemical signalling molecules involved in regulating many aspects of insect physiology and behaviour. In honeybees, compounds including octopamine and tyramine are associated with behaviours involved in foraging and responsiveness to food-related stimuli.
The findings were more subtle than simply showing that glyphosate increased or decreased one neurotransmitter. Tyramine levels showed an interaction between glyphosate exposure and the number of feeder visits made by the bees. In the glyphosate-treated bees, octopamine levels were also significantly associated with levels of its precursors tyramine and tyrosine — relationships that were not detected in the control bees.
In other words, glyphosate exposure was associated with changes in the balance and relationships between chemical signalling compounds involved in honeybee behaviour. Despite the fact that honeybees lack the pathway glyphosate was designed to target, they are negatively affected by glyphosate. How this mechanism works, and exactly what is responsible for these non-target effects in honeybees remains poorly understood.
No research have yet established exactly how glyphosate produces these effects. As a beekeeper, I think this is extremely worrying, especially as products containing glyphosate are still sold as being ‘Safe for insects’.
Conclusion – What does this research tell us about glyphosate and honeybees?
We know that glyphosate was never designed to kill insects. Its primary biological target is a pathway that honeybees do not possess. The herbicide also remains relatively low in acute toxicity to bees. However, this research has proven that the bee does not remain unaffected by glyphosate.
When researchers looked beyond whether exposed honeybees survived and instead measured how those living bees behaved, they found a significant reduction in foraging. When they subsequently examined the bees’ brains, they also found altered relationships among neurochemicals involved in behavioural regulation.
This experiment doe not tell us exactly what happens to a full-sized colony that is exposed to glyphosates, what are the long-term effects or even if glyphosates can enter the human food chain through honey. But it adds another important piece to our understanding of what happens to honeybees exposed to a sublethal dose of glyphosate.
A colony of honeybees depends upon workers being able to perform highly organised, repetitive tasks: finding food, collecting it, navigating, returning home and repeating that activity throughout the day. This research has shown that a chemical such as glyphosate does not have to kill those workers outright to have a detrimental effect. Altering foraging behaviours and brain function may be enough to disrupt the normal functioning of a honeybee colony.
Key Takeaways
Glyphosate is a herbicide that targets the shikimate pathway in plants and microorganisms; honeybees do not themselves possess this pathway.
Glyphosate has relatively low acute toxicity to honeybees, but low mortality does not mean that exposure has no effect on bee physiology or behaviour.
Virginia Tech researchers found that honeybees exposed to 5 mg glyphosate acid equivalent per litre made approximately 13.4% fewer foraging trips than control bees.
The researchers did not detect significant effects on every behaviour examined, including waggle-dance frequency and persistence at a previously rewarding food source.
Glyphosate exposure was also associated with altered relationships among biogenic amines involved in regulating honeybee behaviour.
The precise biological mechanism through which glyphosate produces these non-target effects in honeybees remains unresolved.
Further scientific reading
McHenry, L.C. et al. (2025). Sublethal glyphosate exposure reduces honey bee foraging and alters the balance of biogenic amines in the brain. Journal of Experimental Biology, 228(9), jeb250124.
Hanna Bäckmo is an award-winning beekeeper, entrepreneur, hobby gardener and internationally published writer. Originally from a small island in Sweden, she now lives in East Cork with her son, two dogs, a flock of rescue chickens and lots of bees. Hanna is the founder of Hanna’s Bees, producing a unique range of natural and sustainable honey, propolis, and beeswax products sold in Ireland’s leading Gift & Artisan food stores and select US outlets. With 70 colonies of Native Irish honeybees, she is a passionate bee-advocate and educator and is an Ambassador for the Native Irish Honeybee.
Curious about the world of bees and honey? Join our newsletter to learn something new each week.
In order to make just one single gram of wax, the bees will need to produce approximately 1100 flakes of wax. The wax-flakes are initially clear and odourless. It is only later that the wax will adopt its characteristic colour and smell.
I am often asked if it is true that you should never use metal spoons with honey. There’s a widespread belief that honey should never come into contact with metal. Some people are even insisting that only wooden utensils should be used. But where does this idea come from, and is there any truth to …
How does Glyphosate affect honeybees? New research on foraging and brain chemistry
There is a great deal of discussion about the many chemicals used in farming and what impacts they have on both ourselves and other animals, particularly insects.
Pesticide is the broad term used for substances intended to control organisms that are considered harmful or undesirable. Within this group are insecticides, designed to target insects; herbicides, designed to control plants; and fungicides, used against fungi. Different products target different biological processes and contain different active ingredients. They can therefore have very different effects on organisms that were never intended to encounter them.
One of the most widely discussed is glyphosate, an active ingredient used in many herbicides. It is familiar to most people through products such as Roundup.
What is Glyphosate?
Glyphosate is designed to kill plants. It works by blocking an enzyme called EPSPS within the shikimate pathway, a metabolic pathway plants need to produce particular aromatic amino acids. Once this pathway is disrupted, the plant can no longer maintain normal growth and function and eventually dies.
Glyphosate is used extensively to control weeds, but its agricultural use has not been confined to spraying unwanted plants. Glyphosate-based products have also been used as pre-harvest treatments in some cropping systems, meaning that application may take place close to harvest on crops destined for the human food chain.
The Food Safety Authority of Ireland (FSAI) confirms that glyphosate-containing herbicides may be used as pre-harvest treatments. Glyphosate residues can therefore occur in food. These residues are regulated through legally established Maximum Residue Levels (MRLs). On a side note, there are currently no requirements to label foods where glyphosate-containing herbicides have been used during their production. For more information on glyphosate in food and how residues are regulated in Ireland, see the Food Safety Authority of Ireland guidance on glyphosate.
This is also an area where agricultural practice and product authorisations have changed. In Ireland, glyphosate can no longer be used specifically for harvest management or desiccation of crops. Teagasc notes, for example, that its previous use to aid the harvesting of oilseed rape is no longer permitted. However, pre-harvest application remains possible in certain circumstances for weed control. Teagasc provides further guidance on the changes to glyphosate labels and permitted pre-harvest use in Ireland.
Why would glyphosate affect a honeybee?
Honeybees do not themselves possess the shikimate pathway that glyphosate is designed to inhibit. On that basis, glyphosate has historically been considered comparatively low-risk to honeybees in terms of acute toxicity. In other words, unlike an insecticide designed to interfere directly with insect physiology, glyphosate has no obvious biological target within the honeybee itself.
And, broadly speaking, glyphosate is not highly acutely toxic to honeybees. Its reported LD50 — the dose required to kill half of the bees in a toxicity test — is greater than 100 micrograms per bee. This relatively low acute toxicity helped establish the idea that glyphosate was comparatively pollinator-friendly.
But mortality answers only one question: Did the bee die?
It does not necessarily tell us whether a living bee continues to behave and function normally.
Over recent years, research into glyphosate and honeybees has reported sublethal effects involving functions such as learning, memory, navigation, sucrose responsiveness, sleep and physiological regulation. These observations raise a more complex question about a herbicide that does not directly target bee biology:
What happens to a honeybee that survives glyphosate exposure?
Research from a team at Virginia Tech, published in the Journal of Experimental Biology in 2025, examined that question in an especially practical way — by looking at what exposed forager bees actually do.
What is sublethal glyphosate exposure?
Sublethal exposure means exposure to a substance at a level that does not kill the organism but may still alter its physiology or behaviour. This distinction is particularly important in honeybees.
A worker bee may survive exposure yet experience a change in her ability or motivation to forage, navigate, learn, communicate or respond normally to food. For a solitary animal, such behavioural changes affect only that individual (and their offspring). In a honeybee colony, however, thousands of workers collectively perform the tasks required to keep the colony functioning. Because of this, small changes in individual behaviour can therefore become biologically important when they occur repeatedly across a workforce.
How did researchers test glyphosate exposure in honeybees?
Researchers Laura McHenry, Roger Schürch, Margaret Couvillon and colleagues at Virginia Tech trained honeybee foragers from three colonies to visit artificial feeders.
The bees were divided between two feeders offering the same sucrose reward. The control group received ordinary sucrose solution. The treatment group received the same solution containing glyphosate at a concentration of 5 mg acid equivalent per litre.
This concentration was chosen carefully. According to the researchers, it falls within the range of glyphosate residues previously found in bee-collected nectar three to seven days following application at maximum label specifications. It is comparable with concentrations used in other studies of sublethal glyphosate effects.
The researchers followed 40 control bees that were not exposed to glyphosate and 46 glyphosate-exposed bees. They recorded every visit they made to the feeders during a three-hour experimental period. They also examined recruitment-related behaviour within the colony and later analysed the brains of a subset of the experimental bees.
The primary question was straightforward:
Would bees exposed to a sublethal concentration of glyphosate continue to forage at the same rate as unexposed bees?
Glyphosate-exposed honeybees foraged 13.4% less
Bees collecting the glyphosate-containing sucrose solution made approximately 13.4% fewer feeder visits than bees collecting untreated sucrose solution. The control bees averaged an estimated 31.76 feeder visits during the experimental period. Compared with 27.52 visits in the glyphosate treatment group. However, the researchers did not find a decline in all the behaviours they measured.
Glyphosate exposure did not significantly alter:
in short, the study showed that while the exposed bees were performing less feeder visits, they were still capable of returning to the feeder, entering the colony and participating in recruitment behaviour.
The researchers describe a particularly interesting possible scenario. Foragers encountering glyphosate-contaminated nectar might reduce their foraging frequency while recruitment continues normally. That could result in reduced total nectar inflow while exposure to glyphosate residues within the colony continues.
Why does 13.4% less foraging matter to a honeybee colony?
A honeybee colony depends on repeated individual actions, such as forager bees collecting food. A successful forager leaves the hive, travels to a food source, collects nectar or pollen, returns to the colony, unloads what she has gathered and then repeats the process. Other bees may subsequently be recruited to profitable forage through communication within the colony.
A reduction in foraging by one worker would have little measurable effect at colony level. But a colony’s foraging force consists of thousands of workers. If a similar reduction in activity occurred across a substantial number of them, the cumulative effect could mean less food entering the hive.
The scale becomes clearer when we look at pollen alone. A honeybee colony may consume between 12 and 34 kg of pollen each year, gathered through thousands upon thousands of individual foraging trips. If a substantial proportion of the colony’s foragers made fewer trips, the cumulative reduction in incoming food could become significant over the course of a season. You can read more about the importance of pollen to honeybee nutrition in our guide to pollen and honeybees.
Food coming into the hive is closely connected with activity inside it, including brood rearing and colony development. I explain this relationship in more detail in my guide to feeding honeybees and understanding the colony’s changing food requirements.
The present experiment did not measure whole-colony honey production or demonstrate that colonies exposed to glyphosate collect precisely 13.4% less food. Those would be different questions requiring colony-level studies. What it demonstrates is more fundamental: Sublethal glyphosate exposure changed the foraging behaviour of individual honeybees.
Glyphosate exposure was linked with changes in honeybee brain chemistry
The researchers then investigated whether the behavioural change was accompanied by measurable differences in the bees’ neurochemistry.
After three days, they analysed the brains of experimental bees for several biogenic amines and related compounds: octopamine, tyramine and dopamine, together with the amino acid precursor tyrosine. Biogenic amines are chemical signalling molecules involved in regulating many aspects of insect physiology and behaviour. In honeybees, compounds including octopamine and tyramine are associated with behaviours involved in foraging and responsiveness to food-related stimuli.
The findings were more subtle than simply showing that glyphosate increased or decreased one neurotransmitter. Tyramine levels showed an interaction between glyphosate exposure and the number of feeder visits made by the bees. In the glyphosate-treated bees, octopamine levels were also significantly associated with levels of its precursors tyramine and tyrosine — relationships that were not detected in the control bees.
In other words, glyphosate exposure was associated with changes in the balance and relationships between chemical signalling compounds involved in honeybee behaviour. Despite the fact that honeybees lack the pathway glyphosate was designed to target, they are negatively affected by glyphosate. How this mechanism works, and exactly what is responsible for these non-target effects in honeybees remains poorly understood.
No research have yet established exactly how glyphosate produces these effects. As a beekeeper, I think this is extremely worrying, especially as products containing glyphosate are still sold as being ‘Safe for insects’.
Conclusion – What does this research tell us about glyphosate and honeybees?
We know that glyphosate was never designed to kill insects. Its primary biological target is a pathway that honeybees do not possess. The herbicide also remains relatively low in acute toxicity to bees. However, this research has proven that the bee does not remain unaffected by glyphosate.
When researchers looked beyond whether exposed honeybees survived and instead measured how those living bees behaved, they found a significant reduction in foraging. When they subsequently examined the bees’ brains, they also found altered relationships among neurochemicals involved in behavioural regulation.
This experiment doe not tell us exactly what happens to a full-sized colony that is exposed to glyphosates, what are the long-term effects or even if glyphosates can enter the human food chain through honey. But it adds another important piece to our understanding of what happens to honeybees exposed to a sublethal dose of glyphosate.
A colony of honeybees depends upon workers being able to perform highly organised, repetitive tasks: finding food, collecting it, navigating, returning home and repeating that activity throughout the day. This research has shown that a chemical such as glyphosate does not have to kill those workers outright to have a detrimental effect. Altering foraging behaviours and brain function may be enough to disrupt the normal functioning of a honeybee colony.
Key Takeaways
Further scientific reading
McHenry, L.C. et al. (2025). Sublethal glyphosate exposure reduces honey bee foraging and alters the balance of biogenic amines in the brain. Journal of Experimental Biology, 228(9), jeb250124.
Read the original peer-reviewed research in the Journal of Experimental Biology.
Hanna Bäckmo
Curious about the world of bees and honey? Join our newsletter to learn something new each week.
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