Varroa and Feral Bees: Which is the Villain?

A very controversial point of view.

Associate Professor Patrick O’Connor, of the University of Adelaide, is obviously a lateral thinker (one suspects that he may also sometimes enjoy playing devil’s advocate). In a recent article for The Conversation (the conversation.com June 29th 2022), he explores the notion that the varroa mite could be viewed in a positive light as an effective form of biocontrol for feral honey bees.

Professor O’Connor argues that feral honey bees are a threat to our native biodiversity, as they are both abundant and effective competitors for nectar, depriving native birds, insects and mammals of this resource. He adds that feral bees can change the composition of the vegetative landscape, because they pollinate invasive species (which can be costly to control) and avoid some native plants.

The fight against varroa undoubtedly comes at a significant cost, at both government level, in terms of identifying and destroying infestations, effective surveillance and quarantine and support for affected industry, and for beekeepers, who face not only the loss of a substantial proportion of their colonies, but also increased labour and cost as a result of implementing a varroa management plan. And then there’s the estimated $14 billion of agriculture that is more or less dependent upon honey bees for pollination, coupled with the potential knock-on costs to consumers associated with decreased production or added expense. Alternatively, instead of treating the mite as a pest, Professor O’Connor reasons that if we treat it as a method of biocontrol, this would mean diverting funds otherwise earmarked for eradication and control to projects designed to help us live with varroa. He cites as potential examples increasing the use of native pollinators to assist agriculture, and deliberately releasing mites into feral honey bee hives in areas where native pollinators could benefit the most, such as environments recovering from bushfire. It is also suggested that the destruction of feral honey bees could in fact be beneficial for the commercial bee industry since they compete with managed hives.

Professor O’Connor acknowledges that evaluating the trade-off between potential environmental benefits versus costs to agriculture is not easy. But if we accept that it is almost inevitable that varroa will one day become entrenched in this country, he advocates that we should at least investigate the possibility of using the mite as a biological control, rather than simply committing all our resources to its exclusion. It’s an interesting and thought-provoking proposition.

Nevertheless, the impacts of feral honey bees are controversial and difficult to quantify. And it is an inescapable fact that, like it or not, much of our arable land has been converted to agriculture, and that feral bees are currently valuable pollinators of many crops. There is also evidence to suggest that the genetic diversity provided by feral honey bees may be beneficial; research published in PLOS ONE in 2012 showed that: ‘Colonies with genetically diverse populations of workers, a result of the highly promiscuous mating behavior of queens, benefited from greater microbial diversity, reduced pathogen loads, and increased abundance of putatively helpful bacteria.’

“We’ve never known how genetic diversity leads to healthier bees, but this study provides strong clues,” said co-author Heather Mattila, a researcher at Wellesley College. Hives with more uniform genetics were found to be 127 percent more likely to harbour harmful pathogens than those that were genetically diverse.

Writing in Natural Bee Husbandry, Andy Collins suggests that feral bee colonies are also favoured by being further removed from neighbouring colonies, compared to those in managed apiaries, and that vertical transmission of disease (i.e. from one generation to the next, as opposed to horizontal transmission between colonies) inevitably leads to the rise of less harmful variants of pathogens, since the host organisms must necessarily be able to reproduce in order to transmit the disease. He compares thriving wild colonies with managed colonies in the same area which are treated for varroa and plied with supplementary food to stave off starvation, and concludes that wild colonies benefit from seclusion. Free from the stress of outside interference, he believes this enables them to optimise adaptive behaviour and successfully cope with environmental challenges.

So, is the varroa mite destined to be a valuable method of biocontrol to save native ecosystems from the insidious feral honey bee? Or will feral bees themselves prove to be an essential reservoir of genetic diversity that may one day prove to be the answer to Colony Collapse Disorder?