In recent years there has been a growing concern about harmful chemical residues finding there way into the wax and pollen in the hive. Beehives are exposed to these chemicals by many past and present treatments for varroa mites, as well as the bees returning to the hive carrying pollen laced with pesticides, herbicides or fungicides. It’s not known how long this contamination will last in the frames and to what extent it hinders the health of the bees. Many beekeepers are adopting the practice of yearly comb rotation, thus gradually removing the contaminated frames from the hive.
One recent survey, however, has shown that being too aggressive with comb rotation can increase the chances of winter loss by as much as ten percent.