Queens mate with quite a few drones having different tempered genes. SOMETIMES if we wait, the semen from the mean strain gets "used up" and she naturally goes to semen from another drone's gentler genetic strain. Of course, it could also be a skunk in your locale that is causing the problem. Look to see if there are scratch marks on the front of your hives. I would still requeen all of the hives with a gentler strain and try to get rid of the mean tempered genes in your area. OMTCW