Late Summer checkup and thoughts on Varroa resistance

Here in California we had a very hot summer. For most of June, July, and August we’ve had temperatures over one hundred degrees. Most gardens with full sun exposure did not do very well and neither did bees. We were really able to see the difference between hives that were shaded (or had some shade throughout the day) and those in an open field fully exposed to the sun. On average the shaded beehives fared much better, with the exception being that they attract more hive beetles. As a matter of fact, we barely ever see any hive beetles on the hives that are fully exposed to the sun; But we are spoiled here in California and hive beetles aren’t a big issue at all (at least not for us).

It was the last weekend of August and we hadn’t really done any hive inspections all summer, so it was about time to get out there (in the sweltering heat) and check some hives, especially our spring splits and new queens. About three quarters of the hives we checked were doing very well and had plenty of honey/pollen stores and the rest will need feeding in late winter (to some extent). Unfortunately the hives were too busy carrying water all summer and not foraging. But oh well, at least we get mild winters…

Today, I want to concentrate on some thoughts about breeding for Varroa resistance that were inspired by our recent hive inspections. Specifically, I want to expound on the concept of the constant and ongoing process of breeding for varroa resistance and how (in the near future) we can’t expect our apiary to reach “varroa resistance” to the point that we quit breeding for it.

In our personal experiences, we have found that we can take the most hygienic queen and create a batch of queens from her, yet the degree of varroa resistance (using the term “varroa resistance” very loosely)  in the daughters will vary quite a bit. For example, in a yard of 18 hives, we found one that let varroa get out of control, yet the hive next to it was showing great signs of hygienic behavior. We cannot guarantee it, but it’s very probable that these two hives have queens that are sisters (share the same queen mother). We can guarantee that the grafted queen cells that were put into these hives were sisters, but I suppose that there always exists the chance that one of the queens was superseded (as we only got around to marking the queens during this same inspection).

First, let’s take a look at the hive that was doing poorly. By doing poorly, we mean that it had too many varroa mites, other than that it was full of bees and had plenty of resources (all of the hives at this site are on double and triple deep supers). I have a pretty good eye for varroa and while looking through the brood chamber for the queen, I managed to spot a total of two bees with a varroa mite attached to them. We might let one slide, but not two. As a general rule, if you can see multiple varroa mites, there are many more lurking around, probably in your drone brood.  So we pulled a frame of honey that also had plenty of capped drone brood and sent it to our laboratory for analysis. By laboratory, I mean that I had my two nieces and my daughter pull out larva (drone and worker) and count how many cells were infested (so I can calculate an infestation ratio).  Here are some pictures:

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Based on a sample of 140 drone cells, 76 of them were infested with varroa (that works out to 54.3% infestation). On a sample of 111 worker cells (from the same frame), 5 of them were infested (4.5% infestation). That told us two things: First off, that this queen needs to go. I personally killed her on the spot and we will introduce a frame of eggs from a different hive in a few days (note for beginners: all queen cells need to be destroyed first) for the hive to raise a new queen. Here in California, we still have plenty of drones in September to mate the new queen, so the hive has a good chance of making it.  The second thing that this experiment told us is that indeed varroa mites prefer to infest drone cells whenever possible, but of course, this was no surprise.

A side thought: If a person wanted to treat this hive, they would simply wait about two to three weeks (depending on when you start counting) until all of the old queens’ larva hatched out and treat the hive. Since there is no brood present, all of the varroa mites will be exposed to the treatment and you would get maximum efficiency. If you’re like us and don’t treat your hives, then you just sent the colony into a “broodless” period  and many mites will die of old age without being able to infest the new batch of larvae from the new queen. The broodless method works well for us, but if the hive doesn’t make it, then oh well, we tried.

Now on to the good hive. Ironically, the hive right next to the infested one was doing great and showing very good signs of hygienic behavior. The hygienic bees remove worker pupa that are infested with varroa mites. The pupa that are removed are easy to spot because you’ll see empty cell “gaps” surrounded by capped cells. The tell-tale sign is when you see the removal in action. Before the infested pupa is completely removed, they are first uncapped. The uncapped cells are also easy to spot because you will see the white pupa heads stand out next to the brown wax background. below is a video that shows an uncapped pupa cell and the pupa after we have pulled it out. You’ll notice the varroa mite clinging on to the pupa. The video quality is not great due to us using a cell phone camera and the sun being right over us. However, you can still clearly see the uncapped pupa being removed and the mite attached to it right at 11 seconds into the video.

Below are still pictures that show the uncapped cells and the pupa that we remove from them:

Varroa mite3
Notice how the white pupa stands out in the brown background

In the picture below, you’ll notice all of the “gaps” in the brood. Some beekeepers may mistake this as a bad queen with a spotty brood pattern. But most likely those are pupa that have already been removed.

Varroa mite2
Notice the cell gaps that appear to be a spotty brood pattern

Varroa mite1

We did a quick experiment on the hygienic hive as well. Out of 10 cells that had been chewed open, 8 of them had a varroa mite. We can assume that the bees were at least 80% successful at identifying worker cells infested with varroa.  However, we have no way of knowing if the varroa mites of the other 2 cells had already crawled out before we found that the cell had been chewed open. So the success rate could be (likely is) higher.

You’ll notice in the video above that there is a bee with deformed wings crawling around. That is indicative of the fact that varroa has been present and has infected some bees with Deformed Wing Virus. What makes a “good hive” is not that it is free of varroa, it is the fact  that they know that varroa is present and are doing their best to address the issue. This hive in particular has begun aggressively removing infested pupa as is indicative by the empty cells in the brood chamber (click here to see my post on hygienic bees that deals with this behavior in more detail) as well as the uncapped pupa that we removed ourselves. When we see a hive expressing this much hygienic behavior, we are confident that they will survive on to next year. They prove this year after year and it’s what we call our “survivor bees”.

Those of us beekeepers who open mate our queens have to constantly monitor our hives and cull out any that don’t make the cut. Since our queens are free to mate with whatever drones they choose, their daughters aren’t guaranteed to be as good as the mother. Your best survivor queen can mate with terrible drones and produce terrible daughters. But realistically, good queens produce some good daughters and it’s our job to propagate only the good ones.  In this manner, breeding for varroa resistant bees is a constant ongoing process. Unless we move our bees to an island or instrumentally inseminate our queens, this will continue to be our struggle as beekeepers. The good news is that if you do this long enough, it gets easier and easier as your apiary (and the feral bees around you) develop a “regionalized” varroa resistance.

There are a few traits that we have identified that tell us right away whether a hive will be a survivor or not (Most of them aren’t seen as qualities from a beekeeper point of view).  Maybe I’ll cover that topic in a follow up blog. But for now, we feel good about the status of our bees heading into the fall. We got through approximately 50 hives before the heat made us throw in the towel and we didn’t notice any other hive that showed signs of a severe varroa infestation. It doesn’t get better than that.

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