Effects Of Glysophate On Honey Bees

Research suggests this commonly used herbicide may hamper beneficial gut bacteria, leaving honey bees more vulnerable to disease.

In my campaigning to help the bees, I have tended to focus on the issues of habitat loss and insecticides (primarily neonicotinoids).  True, at times I mention other issues, including diseases and GMO, but one area I have never really covered in depth is the use of the pesticide glysophate and its impact on bees. 

Fortunately, other websites have been doing excellen work in that area, such as weedkillercrisis.com - it’s a great relief – so thanks guys!  

What's The Fuss About Glysophate?

It’s not rocket science that weed killers are pollutants, and that killing ‘weeds’ also means killing wildflowers (and yes, many wildflowers provide food for bees and other pollinators).  However, one particular study listed on the aforementioned website caught my eye, and I felt it was worth highlighting. 


This study specifically draws attention to the harm glysophate can cause to the natural defences against pathogens that exist in the honey bee gut, thereby increasing the susceptibility of bees to disease.  

This is truly alarming!  Cocktails of pesticides (both insecticides and herbicides) are used on many farms (and sometimes on public land).  As it is, neonicotinoids already exhibit multiple ways in which they can increase vulnerability to disease in honey bees (that’s aside from occasions when bees suffer acute poisoning directly).  From the study I will outline below, it seems that herbicide glysophate presents yet another insidious way in which bees can be harmed, by making them more vulnerable to pathogens.

In the case of glysophate, I should just point out that it’s the world’s biggest selling herbicide poison

In highlighting this study, I would also point out that in field conditions, glysophate has been detected in bee hives and honey samples, indicating that glysophate can be inadvertently collected and transported back to the hive by foraging bees (1, 2).

Effects Of Glysophate On Honey Bees:  The Study

Glyphosate perturbs the gut microbiota of honey bees; Erick V. S. Motta, Kasie Raymann, Nancy A. Moran. Proceedings of the National Academy of Sciences Oct 2018, 115 (41) 10305-10310; DOI: 10.1073/pnas.1803880115.

Key Points:

  • Bees rely on bacteria in the gut (‘friendly bacteria’ if you like) that are not only beneficial to the growth of the bee, they are important in the natural defence against pathogens (harmful bacteria) that enter the gut.  In particular, honey bees rely on their gut microbial community to perform a variety of beneficial functions including:

    - food processing
    - regulation of the immune system 
    - defence against pathogens.

  • Therefore, if the gut microbial community is hampered, harmed or distorted in some way, this can, (not surprisingly) have negative consequences on bee health.
  • The herbicide glyphosate is expected to be non-harmful to animals and bees, because it is supposed to target an enzyme found only in plants and micro-organisms.

    Yet the scientists found otherwise.

  • In their study, the scientists exposed bees to glyphosate concentrations that were chosen to mimic environmental levels, and may be encountered by bees foraging on flowering weeds.

    They state:

“Exposing bees to glyphosate alters the bee gut community and increases susceptibility to infection by opportunistic pathogens.” 


“Since bee gut symbionts affect bee development, nutrition, and defence against natural enemies, perturbations of these gut communities may be a factor making bees more susceptible to environmental stressors including poor nutrition and pathogens”.

What do they mean by 'opportunistic pathogens'

An opportunistic pathogen is one that is capable of causing disease only when a host's resistance is lowered.

Here is an example: Serratia marcescens.

Serratia marcescens bacteria is an opportunistic pathogen commonly found in the bee gut.  Ordinarily, the beneficial bacteria would keep it in check, preventing it from causing disease and ultimately death.  

This is unfortunately not necessarily the case in young worker bees exposed to glysophate.  The scientists state:

“Glyphosate exposure of young workers increased mortality of bees subsequently exposed to the opportunistic pathogen Serratia marcescens. 

For bees with a conventional gut microbiota, glyphosate treatment resulted in increased mortality after Serratia challenge”.

In simple language, glysophate increased the number of deaths in young bee workers.  Why?  Because glysophate hampers the bee’s resistance to this particular bacteria (Serratia marcescens) that is commonly found in bees, by hampering beneficial bacteria that fight pathogens.

As an aside, here are a few more interesting notes about Serratia marcescens and its effects on human health:

  • Serratia marcescens is an opportunistic pathogen whose clinical significance has been appreciated only in the last four decades.
  • It has emerged as an important nosocomial healthcare-associated pathogen and a frequent source of outbreaks of hospital infection  in both adult and paediatric patients. 
  • Serratia marcescens is implicated in a wide range of serious infections including pneumonia, lower respiratory tract infection, urinary tract infection, bloodstream infection, wound infection and meningitis. The organism has also been described as an important cause of ocular infection with high incidence in contact lens-related keratitis.

Source: http://antimicrobe.org/b26.asp

Hidden Enemy Of Bees

What really gets me, is that seemingly, manufacturers of pesticides can avert blame because let’s face it, the harm these toxins cause is sometimes indirect. 

First the bee gets the exposure to the toxin.  It doesn’t kill immediately, but through its sub-lethal effects of hampering the bee’s ability to deal with a pathogen that it could otherwise have dispensed with, it is certainly the instigator or facilitator of the death.

But not officially. 

The official killer is the disease itself, not the facilitator.  The facilitator remains distant from the crime of indirectly poisoned bees.

And thus, the regulatory system, already designed to allow poisons to pass through without much challenge, fails to adequately take into account the sub-lethal effects and ultimate threat these toxins pose, especially when used over large areas of land.

It’s not that I’m against business – or even big business necessarily. 

It’s not that I’m against farmers or deliberately wanting to make their lives harder. 

But in my view, big agro-chemical companies have had their way far too long.  I don’t see any evidence of them developing better alternatives, merely recycling their obnoxious poisons, with tweaks. 

Nothing ground breaking.  Nothing to really  help.  And until regulators force their hand, we’ll get nothing new, nothing better, just more of the same. 

We must help the regulators come to the same conclusion - as soon as possible. 

In the meantime, I'll continue to shop organic, and grow my own fruit and veg where I can!


(1) Mukherjee I (2009) Determination of pesticide residues in honey samples. Bull Environ Contam Toxicol 83:818–821.

(2) Thompson HM, et al. (2014) Evaluating exposure and potential effects on honeybee brood (Apis mellifera) development using glyphosate as an example. Integr Environ Assess Manag 10:463–470.