In the backwaters of beekeeping, a bitter debate is raging between the proponents of the so-called ‘mite-bomb’ theory and its opponents who claim it is stuff and nonsense. It isn’t the friendly sort of discussion beeks may have over tea and cake; discussing if you need matchsticks under the crown board when overwintering bees, goodness no, it is a debate with firmly entrenched opinions which each think the other side is either flat earthers or in the pocket of chemical companies.
In short, critics of those beekeepers who choose not to manage mite populations and allow them to die to say those actions kill other beekeepers’ hives. They claim varroa mites travel from the collapsing hives to nearby apiaries and overwhelm healthy hives leading to their demise as well.
This article in Bee Culture provides a more detailed narrative.
I’m not in the business of telling beekeepers how to manage their bees. So, I don’t intend to provide commentary on differing opinions on bee husbandry.
However, I do find the process of how varroa mites move from one hive to another fascinating and if you do too, read on.
The role of cuticular hydrocarbons in hives
Cuticular what now?
Insects’ cuticles, the outer layer, are coated with a layer of hydrocarbons – hence the name cuticular hydrocarbon. Its primary role is to stop the insect drying out. However, it also plays another important role in insects as a means of communication.
There is extensive research demonstrating that the chemicals signatures of these hydrocarbons play and important role in social insects’ communication mechanisms.
For example, in 2003 a study published in Nature described how researchers observed that ants could identify not only the tasks its nestmate was undertaking but also use that information to decide what task it needed to complete.
The context of honey bees you won’t be surprised to find out that forager bees have a different chemical signature that nurse bees.
How does varroa select the bees they hitch a ride on?
To understand how varroa move from a collapsing colony to a new one is it important to understand if varroa has a way to distinguish between different types of bees.
Work done by Dr Cervo and the team determined that given a choice varroa mites had a preference to attach themselves to nurse bees. From the mite’s perspective, a nurse bee will inevitably lead to new brood cell and a juicy fresh larva to raise more varroa on.
As a colony starts to collapse the population decreases to the point that the bees hydrocarbon signature becomes less distinct; resulting in phoretic varroa choosing both nurse and forager bees.
The other consequence of the declining colony population is an increased insistence of robbing.
Varroa will also readily attach themselves to these robbing bees and therefore make their way into other hives.
There is no question that mites have a mechanism that allows them to move from hive to hive, especially, if they have exploited their hosts to the point of colony collapse.
Intervention free beekeeping?
From my perspective, the real mite-bomb debate isn’t treatment or treatment free beekeeping but rather interventionless or interventionist beekeeping.
Being treatment free doesn’t mean you can’t make interventions in the colony to reduce the impact of varroa on your hives. There are plenty of bio-technical measures that can be deployed to manage mite levels within the colony which do not require chemical treatments that mimic how feral colonies are coping with varroa in the wild.
If you aren’t intervening in your colonies, even just to monitor health, you probably aren’t beekeeping.