I received many well-reasoned responses to yesterday’s post about the spread of varroa mites. Rather than attempting to answer them separately, I decided to write a follow-up.
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Honey bees have naturalized in North America
You are absolutely right that honey bees are not native to North America. But from the time they were imported by the colonists in the early 1600s, until the introduction of the varroa mite in 1986, honey bees naturalized across the continent. They thrived and could be found nearly everywhere. But all that ended when the varroa mite entered the feral stock and, for all practical purposes, wiped it out.
Some estimates in the scientific literature put the remaining feral stock at about 2% of pre-varroa levels. Other accounts say the number is zero, and any seemingly feral colonies simply escaped from managed hives within the last two years and will not survive.
I’m not an expert on this issue, but I’ve heard many accounts of hives that have persisted for more than a decade and are still going strong. I believe at least some of these stories, so I tend to side with the 2% group.
Drifting bees transmit mites as easily as swarms
One of you wrote that it wouldn’t be necessary for bees to swarm to transmit diseases to the wild stock. You point out that the spread would happen naturally as populations of bees mix together. That is also true. In my post yesterday, I was not suggesting we could protect wild populations by keeping our bees from swarming. Not, at all. My objection was to the idea that we are somehow helping populations of “all bees” by letting our swarms go.
I don’t believe swarms on the loose are going to help or hurt feral colonies—not at this late date. But there are many reasons to manage your swarms, especially if you are an urban beekeeper.
Besides, if “helping the bees” were that simple, we could all let our swarms go this summer and the whole bee crisis would be over in one season.
Survivor stock may fail under different environmental conditions
Several of you wrote that if we let managed swarms escape, the principle of “survival of the fittest” would take over and before long these colonies would morph into varroa-resistant, disease-resistant stock. That would be great. That is what we all want. But so far, it hasn’t happened. Many of the feral colonies that have been used as “survivor stock” have not persisted under managed conditions—a situation that suggests environmental factors, rather than genetic ones, kept them alive in the wild.
The honey bee genome is a flaky thing. Whereas almost all insects evolve tremendously fast—think mosquitoes and cockroaches—honey bees do not. They do not have the wide array of genes for detoxification and disease resistance that other organisms have. A creature cannot evolve if the genes don’t exist, and this seems to be particularly troublesome in honey bees.
The theory is that these genes, if they ever existed, were lost as the honey bee became a communal animal. In honey bees, disease resistance is a colony function where individuals sacrifice themselves if they become ill, and where cleanliness—including the removal of parasites, dead bodies, sick bees, imperfect bees, pathogens, mold, and mildew—is practiced relentlessly.
Like wearing a breathing mask when the flu arrives, these are mechanical rather than immune responses to disease. (Although the mechanical behaviors are themselves genetically transmitted, there is a distinct difference in the mechanisms.)
So far, we have found no reliable genetic answer to varroa in America
Breeders who are trying to raise varroa-resistant stock are concentrating on these hygienic behaviors, rather than simple genetic resistance, which is so rare in honey bees. Although there has been some notable success in producing varroa-resistant strains, the resistance essentially disappears when these special bees are bred back into the general population.
Now, 26 years after the introduction of varroa, we still don’t have a viable solution to the problem. It would take an extraordinary genetic mutation to suddenly provide resistance to varroa—or at least to the viruses it carries. Extreme mutations are rare in any species, but in a social organism where only a few individuals pass on their genes (the queen and a few drones), it is even less likely to happen.
Honey Bee Suite