The short answer is:
When rigorously interrogated, there is no robust scientific evidence that honey bees harm wild bees. Furthermore, when honey bee colonies were in decline due to the demise of beekeeping, a population increase in wild bees did not occur.
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:
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:
community studies showed potential effects, both positive and negative, but did
not show direct or long-term effects of managed bees on plant community
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
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.”
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.
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
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:
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.
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.
I think two huge issues need to be considered here:
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".
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.
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.
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