Do Honey Bees Harm Wild Bees?

  • Concern has grown in recent years that managed bees might have a negative effect on wild bees.  For example, major UK national newspaper, The Daily Mail, featured an article titled: 
  • “Beekeepers are blamed for fuelling the decline of wild bees by breeding insects purely for honey and reducing easy access to pollen”(25th Jan 2018), and on the same date in The Daily Telegraph: "Urban beekeeping is harming wild bees, says Cambridge University".
    But are these concerns balanced and valid?
  • In December 2017, a scientific paper was published which reviewed all 146 available scientific studies from 1900 to 2016, examining the effects of managed bees (both managed honey and bumble bee colonies) on wild bees.  
  • The topics covered by the papers were: competition over finite resources (nectar, pollen, nest sites); impact on plant communities and spreading of pathogens.
  • Despite most of the papers suggesting that managed bees have a negative effect on wild bees, many studies to date do not show direct or causal relationships between managed bees and wild bees. That is, studies lack controls or experimental manipulations, or do not measure critical parameters such as wild bee fitness, or population-level.  Other factors, such as the relative effects of habitat loss or pesticide exposure on wild bee populations (versus effects of managed bees) are unknown and potentially confounding.  These factors are not considered within the reports.  Further, some studies indicate that managed bees had a positive effect on native plant communities.



The Study

An important review:
"Do managed bees have negative effects on wild bees?: A systematic review of the literature" by Rachel E. Mallinger, Hannah R. Gaines-Day and Claudio Gratton at the University of Florida(1), was published in December 2017.

The studies covered the following topic areas:

  • Competition over finite resources such as nectar and pollen, or for nesting habitat:
    72 of the studies addressed competition, the majority of studies (59) focusing on competition from managed honey bees Apis spp, 17 focusing on managed bumble bees.  
  • Plant communities: for example, managed bees might affect resource availability for wild bees by changing plant community composition, for example, by helping to pollinate and spread plants that out-compete native plant species essential for wild bee survival.
    41 of the studies addressed plant communities,  36 of which focused on honey bees, and 6 focusing on managed bumble bees. 
  • 6 of the studies examined both competition and plant communities, (2 honey bee studies, 5 bumble bee studies).
  • The spreading of pathogens:  could movement of managed bees across regions (especially outside their native ranges) encourage the spread of diseases through the contamination of pollen, faeces, or contact on shared foraging resources?
    27 studies addressed spread of pathogens, with studies being more evenly split between those studying managed honey bees (n = 15) and managed bumble bees (n = 10)



Findings

Mallinger et al found that whilst most of the studies claimed a negative impact of managed bees on wild bees, most of the studies failed to produce causal links, and in some areas, results were mixed:

“These conclusions may support the use of the precautionary principle when employing managed bees, particularly in or near areas with species of conservation concern. However, most of these studies did not measure wild bee fitness, population, or community-level responses including reproductive rates, survival, abundance, or diversity, making it difficult to draw long-term or broad-scale conclusions about the effects of managed bees. Furthermore, some studies found positive effects of managed bees, particularly on native plant communities, indicating that in some contexts, managed bees may aid in restoration or conservation efforts.”

In other words, in environmentally sensitive areas, some caution might be advisable before introducing managed bee colonies, however, it’s also clear that the studies drew conclusions without properly establishing cause and effect relationships, and there is some evidenc that managed bees my have a positive effect on native plant communities. 

With reference to competition for food resource, Mallinger et al say:

"Like the previous reviews, we conclude that there is evidence for the presence of competition between managed bees and wild bees, though there is little evidence that this competition can lead to wild bee population declines.

For instance, the majority of competition studies examined how managed bees affect wild bee foraging behaviors, in particular visitation rates to different flowers.

How changes in wild bee foraging behaviors translate to variation in wild bee abundance or diversity was rarely studied. Since many bees are generalist flexible foragers and can partition resources in the presence of other bee species, changes in foraging behaviors may not necessarily have population-level effects.

In order to fully assess the effects of competition on wild bee populations, more studies that include measures of wild bee reproductive success or abundance as a function of managed bees are needed.

While it may be more challenging to document long-term or direct effects of competition on wild bees, relatively recent studies provide good examples of how wild bee fitness or population-level responses can be evaluated."

With reference to impact on plant communities, the review states that they found: 

 “most plant community studies showed potential effects, both positive and negative, but did not show direct or long-term effects of managed bees on plant community composition”.

On this point, they conclude:  

"Thus, based on the literature we reviewed, the overall effects of managed bees on wild bees via changes in plant communities remains speculative".

On pathogens, whilst they acknowledge that the literature to date suggests that managed bees can transmit pathogens to wild bees, and that these pathogens may be contributing to wild bee population declines, Mallinger et al also point out: 

“However, these studies have similar limitations to those on the other topics, including that they do not show direct, long-term, or population and community-level effects of managed bees on wild bees.”

Important Considerations Missing From The Studies

It seems that whilst looking for impacts of managed honey bee colonies and bumble bee colonies on wild bees, researchers have neglected to take into account other important environmental factors:

“While our review found a substantial amount of research on the interactions between managed bees and wild bees, the relative effects of managed bees compared to factors such as habitat loss or pesticide exposure on wild bee populations are unknown and potentially confounding.”

Study Conclusion

This nails it for me from the paper:

"Our review found that the majority of studies reach the conclusion that managed bees negatively affect, or have the potential to negatively affect, wild bees through competition, changes in plant communities, or transmission of pathogens.

However, there was significant variability in study results, particularly in the areas of competition and plant communities, with some studies finding no or even positive effects of managed bees.

We also found that many studies to date do not show direct or causal relationships between managed bees and wild bees. That is, studies lack controls or experimental manipulations, or do not measure critical parameters such as wild bee fitness, population-level, or community-level responses to managed bees.

While such studies can be logistically challenging, thereby limiting their number, recent studies provide examples of novel approaches, large-scale experiments, and/or the use of long-term data in order to better understand the effects of managed bees".

My Comment

When seeking to find out whether or not managed bees have any form of impact on wild bee populations, reproductivity or health, I think it's important to ensure the questions have been properly examined and researched, so that the real problems are identified, questions and answers are relevant and adequate, and research output is scientifically robust. 

Conservation-minded scientists cannot demand robust science from vested interests if they are not going to adhere to such principles themselves.

Here are my personal observations and specific comments relating to the subject matter covered in the review:

Competition

I agree with Mallinger et al: research must do more to establish cause and effect, rather than speculate, and in my own personal experience, I see no evidence for competition as being a causal factor in wild bee decline.

  • I have observed various wild species of solitary bee engaging in territorial behaviour to great effect, apparently taking control of patches of flowers and chasing off competition from other bee species (example: wool carders chasing off bumble bees and various solitary species).  I have literally observed bumble bees physically removing honey bees and shunting solitary species from flowers.  Likewise, I have observed mason bees shunting honey bees and smaller solitary species and flies.
  • In the UK, until the very recent upturn in the number of beekeepers and beehives (post 2010), beekeeping was on the decline.  In fact, in England the managed honey bee population fell from 182,000 registered colonies in 1965 to 179,000 in 1985, then 15,000 beekeepers managing just under 80,000 colonies in 2008. During this time period, wild bee populations did not increase in response, but actually declined, and some species became seriously threatened (with some extinctions).
  • In addition, personal observations of seeing lots of bees on one plant in one year but not in the next year, does not demonstrate cause and effect - (I have seen and heard such complaints - for every person who says "since the honey bees arrived, I see fewer bumble bees on my XYZ plant", there are many who report no such effects - that includes myself.  However, I have found bumble bees to be less active in my garden as soon as the comfrey in the verges around the corner is in full bloom, which huge numbers of Bombus seem to prefer to what's on offer in my small patch.  I felt uncomfortable about the bumble bee numbers until I discovered the reason - on the other hand, bumble bee predators could have been the problem otherwise).
  •  I recall BBC Radio presenter, Verity Sharp interviewing a range of views, as she and her husband installed bee hives in  their garden. She and her husband made a very valid point: without the attention to bees and installing hives in the first place, they would not have contemplated turning over their garden and lawn to flowers for pollinators.  From their personal observation, they now see far more wild bees in their garden than ever before, not merely the honey bees. 

    As an aside from this, the bees campaign was initiated primarily by beekeepers and myself - not conservation organisations.  In the UK, there was a very small team including myself, who generated the momentum from 2008/09 onwards.  Most UK conservation organisations refused point blank to be involved in the campaign, until 2012 following the release of the EFSA report that independent campaigners and beekeepers campaigned so hard for.  

Plant Communities

In line with the researcher's recommendations, I tend to advise caution against setting up bee hives in environmentally sensitive areas. 

A few years ago, a visitor to this website who happened to live next to an SSSI (Site of Special Scientific Interest) was considering installing a bee hive.  My advice was not to do it.  Beekeepers have a tendency to plant additional flowers in their gardens. The seeds from the cultivated plants could easily blow into the SSSI, thus out-competing vulnerable wildflowers to the detriment of the species that depend on them, and potentially even changing soil structure and pH balance.  Although competition for nectar and pollen is not established, applying the precautionary principle in such a scenario would seem like common sense.  You can read more about it here.

Pathogens

I think two huge issues need to be considered here:

  • Biosecurity - certainly, because of relaxed border controls across Europe, the transmission of parasites and diseases (even between managed colonies) has become easier -for example,  Varroa mite - was first detected in Britain in 1992 and came over with imported bees. 

    It appears that with the relaxing of borders, lessons had not been learned from the past. 


Phil Chandler, the Barefoot Beekeeper, referring to the native Black Bee in Britain, (honey bee Apis mellifera mellifera), and the beginning of the importation of bees from overseas, with the introduction of the Isle of Wight disease in the early 1900s, comments:

"However, she [the Black Bee] had an Achilles heel, which almost caused her extinction - a fatal susceptibility to viruses carried by an internal parasite that was imported along with Italian bees. The Black Bee was decimated by "Isle of Wight Disease", as it became known".

From:  http://www.biobees.com/blackbees.php

Secondly, previous work on commercially-reared bumble bees has pointed to the need for those commercial companies to take better care - for example, ensure bees are not fed contaminated pollen.  I whole-heartedly agree with Mallinger et al, that growers using commercially reared bumble bees in greenhouses can take more stringent methods to ensure bees don't escape into the wild.  However, with regard to general use, it would be better to have a healthy environment that enables wild bees to thrive, such that the commercial rearing of bumble bees is not necessary.

Other Glaring Omissions

Whilst I can't claim to have read all the studies Mallinger et al have examined for the purpose of this review,  I have to say that I have previously looked at a few of them, and have remained unconvinced.

  • I have yet to find a study that adequately takes into account the environmental factors, as pointed out by the Mallinger et al, especially over time.  For example, no consideration was given to pesticide levels in the environment, with a very detailed examination of floral abundance and variety.  Researchers need to be very clear in their knowledge of honey bees and beekeeping.
  • I have yet to find a study that actually compares what happens to the populations of the wild bees in various locations, versus the populations of the managed bees at the same time - especially with regard to the honey bee colony.  For example, are the managed honey bee colonies performing as well as can be expected?  If wild bee populations have suffered, how do we know that the honey bee populations have not suffered too, or the colony hampered in some way for the long if not short term?  Do their hive products reveal evidence of chemical contamination?

Please focus on the real problems

Other insects and invertebrates are suffering declines. We already know that habitat loss and degradation is a serious problem. Perhaps researchers should ask whether the problems being faced by so many invertebrates - including aquatic species, actually has a common factor, such as pollution from insecticides, intensive agriculture.  
Clearly, there is a wider, environmental problem here. 

However, for the sake of wildlife, it's important, please, to focus on the right issues - with robust research.  

(1)  Copy and paste this link in your browser to see the full study - it's freely available for viewing: https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0189268

Worldwide Insect Decline - Read







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