Today I have a less fortunate topic to write about. Sadly one of my hives died.
As for the reason I can confirm that it was due to a too heavy Varroa infestation, that weakened the hive, and in the end most bees and the queen were gone. Very typical.
To get some value in learnings out of this loss I am going to lay out the history of the hive, and what exactly went wrong, i.e. what mistakes I made.
The history of the hive
To start with the hive overwintered well with a 1-year-old queen, that had done well the year before, thus this year I kept her going, and also reared a few queens from her. The hive was healthy coming into spring and had already filled a honey super by mid-November. We always do get very early flows here, that taste amazing, so I am always keen to get that early honey harvested.
So far everything went well, but unfortunately just before Christmas the hive started rearing swarm cells, which is perfectly normal for a strong hive. Giving them as much space as possible did not persuade them otherwise. I was breaking the swarm cells, but must have overlooked one so of course the hive swarmed. While I did catch the swarm, they also absconded from the box that I put them in. Much to my surprise 2 weeks later the hive swarmed another 2 times.
The hive that was left had lost most of its bees (as they had swarmed off), but they had a virgin queen and plenty of stores. I removed the honey supers (shook off most of the bees first), and put them onto another hive because the now very small colony did not need as much space. Of course, there was still plenty of honey left in the brood box.
The queen eventually got mated and started laying and while being a weak colony it did look good and healthy, and I was confident that they would build up a strong colony until the start of winter.
Now is when things went wrong. As the colony still looked healthy I waited with its varroa treatment until the honey supers had come off the other hives, so I could insert strips into all hives at the same time. As last year I intended to use oxalic strips, but I had to make them first.
What I did not do (but should have done) is to do a mite wash (or sticky board count). I simply assumed it was still fine because the hive looked healthy. Eventually though the first signs of bees with deformed wings showed up. Just one or two, and it still did not look too bad. But they caused me to finally get those strips done and put them into the hive.
About two weeks later I noticed quite strong activity with the hive, which I correctly interpreted as robbing behavior. I reduced the entrance to help them with the robbing, and after a cold spell of 2 days I did another inspection, to see what was happening.
Sadly at that stage the hive was already doomed. The queen was gone, and there were no eggs. Most bees were busy helping themselves to on the honey stores (that were still there) and there were a few young bees, and many with deformed wings. The brood cells now also clearly showed signs of pms, which I had not noticed earlier.
I thus decided to “cull” the colony, by shaking the bees to the ground and storing the frames away so bees could not access them. Any healthy bees would eventually fly off and make their way to other colonies, any ones with deformed wings obviously died. Most of the mites and the viruses are still trapped in the capped brood that I stored away. My plan is to melt those frames which will kill any diseases. There were no signs of AFB, so spores should not be a problem.
So, what have I done wrong?
I clearly underestimated the Varroa mite infestation level of the hive initially, and when I realized that the mite levels were quite high, I used a treatment that was not fast-acting enough.
Let me explain further.
Seeing bees with deformed wings is always a sign that varroa mites are present, it is also a clear indicator that the infestation has already reached a critical level and treatment has to be done urgently and immediately. Normally they are a sign that you actually are already too late.
While oxalic strips are a good tool in the fight against varroa, they act very slowly, meaning they will not immediately knock back an already critical mite infestation, but are only able to slowly decrease the mite load over the course of multiple weeks. This means that they are only good at gradually decreasing the mite infestation of a healthy colony, which in the case of my lost hive was way too slow.
I have 3 hives next to the now dead colony, that were all treated with oxalic strips at the same time. However, while being healthy, they also show early signs of deformed wings. I thus removed the oxalic strips and replaced them with a stronger and quicker (but non organic) synthetic treatment.