Hlo Grace,
Two weeks ago we put Varroa strips in our four hives. This weekend we noticed zero activity in a hive that had been hopping two weeks ago. Popped the lid to find it absolutely empty of girls. All honey was gone too. There were a few dead bees and some hornets inside and a pile of dead bees in front of the hive, plus four hatched wax moth cocoons under the bottom board. Brood was abandoned. We’d put under-filled honey frames from the other hives out for the bees to recycle the honey into their brood boxes. Could this have sparked a raid by the other three hives. Given the timing, this is unlikely to be a Game of Drones activity. Ideas?

So sorry to hear you lost a hive. It is possible you triggered robbing. If they were the weakest hive, they may have become the target. The wasps could have contributed. What was the varroa count before you treated and was that the first time you treated this season? High varroa counts often result in a dead hive in fall and they go really quickly if robbing happens at the same time. I have had really no problem with my queens using Formic pro. But, others have lost queens when using it. Losing a queen can make a hive less likely to defend itself. Once robbed out, remaining bees will often abscond. I would definitely check the other hives for varroa numbers and consider a OA treatment this month. Let me know what you find in the other hives for counts.  –Grace

Thanks for your reply and thoughts. We didn’t see hardly any “pepper” on the varroa boards under the hives during the summer, and didn’t want to treat them while they were working on honey for consumption. We figured it’d be good to dose them as part of winding down for the winter, and inserted Apistan strips, one in each hive. Who knows. Maybe the strip nailed the queen while inserting it between brood frames. Looks like all the brood had hatched. Very few dead ones at the bottom, but a small mound, maybe 100, in front of the hive. Disappointing, but we still have the other three to teach us about bees.

Apistan is an old treatment and has a considerable amount of resistance from mites in many areas.  It is also one of the chemicals that stays in the wax making it toxic after a few years.  It definitely should not be used with honey supers on.  The recommended summer treatment for mites is Formic Acid in the form of Formic Pro.  As a naturally occurring organic acid, it can be used with honey supers on and quickly dissipates in the hive.  It is always possible that you killed the queen. The observation that all the brood hatched, implying that the brood was healthy, is a good sign.  But, waiting so late in the season to treat and not testing is a recipe for disaster. I do hope your other hives are good.  If that is the case, then you will probably have an opportunity to split in the Spring.  I do not recommend using Apistan at all.  If you want to use a chemical (as opposed to the organic acids like Formic Acid or Oxalic Acid), then I recommend Apivar which has not shown significant resistance and also leaves very little to no residue in the wax. –Grace

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