In the temperate regions of the northern hemisphere, August is a critical time for mite management. Every year I find it hard to think about mites during spring and summer since they are nearly invisible. At that time of year, nearly 90% of all mites hide within the capped brood cells, out of sight and out of mind. So unless you are in the habit of plucking pupae from their cells, you hardly ever see a mite. Your sticky board counts are low and your colonies are booming. Mites, it seems, are not the problem everyone talks about.
But it all changes in the eighth month. Sort of. It actually began to change at the summer solstice, back in June. That’s when your colony growth rate began to level off. Although hardly noticeable at first, the queen lays fewer and fewer eggs per day and the colony gradually shrinks as the weather warms into July and August.
Mite populations rise as bee populations fall
But while the bee population declines, the mite population continues to rise. More gravid female mites roam the hive looking for soon-to-be-capped brood cells where they can lay their eggs. If there are not enough brood cells, the mites will even double up and share the ones available. And by August, the colony is tired of drones and is actively expelling them. The queen isn’t laying many drones either, so all the female mites opt for what remains: worker brood.
Left untreated, an average-sized colony that may have had 6 mites per 100 bees at the end of June, may find itself hosting 35 mites per 100 bees by September 1, a nearly seven-fold increase. Assuming you started the season with zero mites, the rate of increase is dependent on the number of mites that joined your colony during the spring and summer.
Mites can arrive in many ways but drifting bees, especially drones, probably bring in the most. A colony with ten introductions could end up with five times as many mites as a colony with two introductions, depending on when they occurred.
More mites carry disease to more bees
A six- or seven-fold increase in the number of mites per bee means a similar increase in the number of bees infected with the viral diseases that mites spread. Worse, by fall the mites are not divided among the drones and workers but reside on the workers alone.
While the number of mites per bee gradually rises in June and July, by August it literally explodes. Unfortunately—and here is the real kicker—the worker bees that are reared in September and October are the bees that will see the colony through until next spring.
Winter bees can’t afford to be sick
While a spring or summer forager may live a mere four to six weeks, a so-called winter bee (or diutinus bee) may live up to ten months. Since these long-lived bees care for the colony during the cold and confined winter months, they cannot be sick at the beginning or the colony will not survive.
To raise healthy bees in September and October, your colony needs to be virtually mite-free by the end of August, the very month that the mites-per-bee ratio explodes. So if you are going to treat your hives, August is the month to do it.
Timing is everything
For many years, I read that any treatments should be completed by August 31. But lately I’ve noticed that many groups are recommending an August 15 completion date for the best shot at healthy winter colonies. That means if you are doing a three-week course of something like ApiLife VAR, you should have already started.
Many beekeepers like to treat the mites in August and then again in the dead of winter when little capped brood is present. A second treatment in winter may be especially important in very strong colonies that robbed other colonies in the fall. Robbers often attack a weak colony that is dying. In addition to bringing home the honey, they bring home the mites as well.
But however you decide to proceed, remember that timing is everything. The ultimate goal is to raise a crop of disease-free bees that can take care of themselves from fall until spring.
Honey Bee Suite