Varroa Mites Are In Your Hive

Yes, I know – another post about Varroa mites. Just back from holiday and as I wrote this for our beekeeping association magazine recently I thought I’d recycle it. It means I have more time to see if my queens have mated and whether all of my hives are full of queen cells!

Worse than you think?

It’s human nature to avoid pain, so when we find out that our bees have dwindled to a miserable sickly cluster or have died, we don’t want to admit that it might have been our fault. As custodians of livestock, I believe that beekeepers are responsible for getting educated about bee health and diseases. The recent ‘bee health day’ organised by our Stockport branch of Cheshire BKA is an excellent way to imbibe much knowledge quickly. From the many research papers, books and articles I have seen – and from conversations with bee farmers – it’s my view that Varroa mites cause the death of more colonies than most people admit.

Nature is harsh

On the plus side, the plight of bees in the wild is pretty rough anyway. Bees that make homes in trees, chimneys, and so forth often succumb to the weather, Varroa mites, or misfortune. Beekeepers who provide a comfortable home for their bees, feed when necessary and monitor for pests and diseases give them an excellent chance to thrive. Nature being what it is, sometimes things die – it’s a way to sort out the wheat from the chaff. Part of looking after bees is identifying positive or negative traits and increasing the former while removing the latter. That’s one reason to raise queens from your strong colonies, not the small swarmy stingy ones.

Vive la resistance

One trait that most beekeepers would love to find in their bees is that the bees somehow find ways to resist the ravages of the Varroa mite. Many studies have looked into such things, and clearly, Varroa resistance exists in some localised areas. Some beekeepers attempt to breed resistance through the so-called ‘Bond Method’ (live and let die). The resistant trait can be propagated in isolated areas by allowing non-resistant bees to die out and raising queens from the survivors. Of course, most of us do not live on a remote island or peninsula, and our queens mate on the wing with whatever drones are about. With hundreds of colonies within 10km of our hives, we cannot control the drone side of the mating equation.

How many mites do you have?

In my small and probably inconsequential way, I am trying to ‘do my bit’ for the bees by raising queens from colonies with low mite numbers. I have to monitor mite numbers using a reliable test to do this. For me, that means testing a sample of bees using an alcohol wash. Simply looking at the natural mite drop onto a Varroa board is not as reliable as the alcohol wash. To me, the Varroa board is for observing mite infestation after treatment with a varroacide (amitraz, thymol etc.). It’s ‘after the horse has bolted’, but you can clearly see, after treatment, how many Varroa mites were killed.

Treatment threshold

I do an alcohol wash mite test on all of my production colonies in June. That’s over thirty colonies, which takes a while. Still, it gives me valuable insight into the differences in mite levels across all of my hives. Randy Oliver tests all one thousand colonies in his sons’ operation in California! If my winter oxalic treatments were not very effective, the mite numbers would get too high by June. Anything over six mites from a sample of 300 bees (2%) is too high – some form of treatment is required.

When I find high mite levels, I can’t be sure whether it’s because my winter treatment failed or that those bees are somehow more susceptible. Either way, they are ruled out of queen rearing and treated so that they don’t die in late summer. The oxalic acid treatment does not work on mites underneath brood cappings, and colonies often have some brood over winter.

Alcohol wash

So, going back to our responsibility to our bees, it makes sense that we should test mite infestation levels. I think June is a good time. Even if we aren’t doing some fancy breeding program, we can spot the colonies that need help.

I use the Varroa Easy Check device with so-called ‘rubbing alcohol’ to do my mite washes. The sample of bees is taken by shaking a frame of bees from the edge of the brood nest into a tray, ensuring that the queen isn’t on it! I scoop up a half cup measure (118ml) of bees into the shaker containing alcohol. The bees instantly die, but they do so for a good cause. The mites are dislodged and visible in the bottom after rotating and shaking the container for about 40-60 seconds. I record the number of mites and later use this information to decide on breeder queens for next year.

Summer treatment options

When treating the colonies with high mite levels, if you use a mesh floor and have the monitoring board in place, you will see how many of the nasty little suckers you have killed. Personally, I don’t use MAQS or Formic Pro, but many people do with great success. I go for VarroMed, a trickle solution containing oxalic and formic acids. Heavily infested colonies need about three treatments five days apart, and the supers should be removed at that time. Of course, if your hive is broodless, only one dose is sufficient because the mites are not hiding under cappings. Bear in mind that these colonies are probably doomed unless you intervene.

On the spectrum

We now have a spectrum of interventions concerning Varroa mites. There is the ‘leave them to it’ Darwinian beekeeping approach, in which many colonies will die. Not only that, they are robbed by other bees in the neighbourhood, spreading the mites far and wide. As you can tell, I’m not a fan of that one. Then, at the other extreme, you can just treat everything, assuming that they all have mites anyway. Some people routinely treat at the end of summer, winter, and early spring without ever testing for mite levels. The problem is that mites tend to develop resistance to treatments over time, plus you will not spot colonies that manage to regulate mites on their own. I’m somewhere between those extremes. I still lose colonies (10-20%), but I think I’m doing the right thing.