I have been watching the goings on in one of my hives with great interest. A swarm left the hive on 2nd July and I released a newly emerged virgin queen into the hive on the same day. When I looked in each time subsequently I didn't see the queen but she was obviously laying well, with plenty of eggs and a normal brood pattern. I treated the hive for varroa on 16th July with formic acid strips (MAQS). I looked in with the bee inspector on 31st July and all seemed well but there were two charged unsealed queen cells. Although the MAQS instructions say to leave them we decided to remove them. I next looked in on 7th August and there was one sealed queen cell, three charge unsealed cells, and three empty cells, all of which I removed. At the next inspection on 15th August there were another four queen cells so this time I gave in and left them all. In all this time I had not seen the queen but she continued to lay well.
On 25th August I found the queen on the second frame and marked her yellow. Then three frames farther on I found another queen and marked her yellow as well. I presumed that one queen was the original from July and the other was new but obviously I didn't know which was which. In addition there were three or four torn down queen cells and two more charged queen cells which I left in place. No photos as all this caught me by surprise.
Next time on 30th August I was prepared with a camera and I easily found a yellow marked queen.
Then on the next frame I found the other queen.
Both the latest queen cells had been taken down and this was all that remained.
I presume this is supersedure, perhaps triggered by the MAQS treatment, but it does seem odd to supersede a seven week old queen who is laying well and producing a normal brood pattern. I assume the bees know what they are doing. The only frustration is that I don't know which queen is which so if at some stage there is only one left I won't know if it is the new one or the old one. It has also been interesting to see how persistent the bees were in raising new queen cells once they had decided that's what they wanted to do, and how they took down the other cells once they had got what they wanted. I'll know better next time to leave them to it.