Controlling Varroa by Disrupting the Brood Cycle

Chemical-free Beekeeping: Controlling Varroa by Disrupting the Brood Cycle
--By Warren Miller, President, Pennsylvania State Beekeepers' Association

To keep bees in the 21st century, you have to be part farmer and part scientist. Sometimes it seems like you have to be part alchemist as well. I've been keeping bees for about 25 years. For me, it was love at first sight. I can think of few greater pleasures in life than working with bees on a sunny day.

I have a few small beeyards and manage 75 hives in central PA. In the past several years I've been able to improve the survival rates of my bees by approximately 300%--all without the use of chemicals. I attribute my success to a few related factors. About ten years ago I started raising my own queens. I've been making sure that my hives go into the winter with a young queen that is acclimated to northern conditions. Annual re-queening offers some promising benefits; however, unless you get the timing right, it isn't enough to appreciably increase colony survival rates. Timing is everything.

If you do the math, you realize that I got involved with bees in the mid 1980s—right around the time when all of the trouble with Varroa began. Like most beekeepers, I suffered some pretty significant losses in those days. At the time, I tried to combat my losses with chemicals.

For eight years in the 1990s I used Apistan strips. Some of the treated hives lived, and some of them died. I'm a frugal guy. I started wondering why I was spending money on treatment that didn't give consistent results. I was also getting a little resentful, because I realized that I was spending my time managing mites when I really wanted to be managing my bees.

So, in 1999, I stopped using chemicals to treat my hives. My first year, I lost 80% of my 12 hives. Typically, I'd have 3 to 4 hives make it through the winter. Usually, one hive would stand out as a good producer. I started paying attention to that hive. A lot of researchers are paying attention to sick hives. I think there's something to be said for paying attention to the healthy hives as well.

Initially, I started re-queening my hives with the daughters of my best hive, and got improved results with respect to survival and production. Then I started raising my own queens.

In 2002, I lost 75% of my hives.

Now, I lose less than 20% of my 75 hives.

To be successful with bees, you have to know your enemy. In 2004-2005 I learned as much as I could about the mite lifecycle. The science confirms what we see as soon as the weather starts to get warm: that honeybees and mites are in a race in the spring to produce as much brood as possible. However, unlike the mite lifecycle, the honeybee brood cycle is influenced by the presence or absence of a nectar flow. After the nectar flow has peaked, the honeybee queens reduce their egg-laying. As a result, brood production decreases.

As you can imagine, this is the time when the mite population can really escalate. In early spring, when brood and mite populations are increasing, a hive might have approximately 20% of brood cells or less infested with mites. In mid-July, however, with fewer bee brood levels and increasing mite populations, 80% of a hive's brood cells or more might be infected. By interrupting this cycle, you can improve both honey production and hive survival rates by reducing the number of honey bee brood cells harboring mite reproduction.

Here's what I recommend, and why. Note that the times are dependent on the honey flow, and that you will have to tweak the timing of this method if you live somewhere other than central PA (Zone 5).

  1. Pull queens out of the hives at the beginning of the honey flow. Here in central PA, this usually is around the week of June 1. Your objective is to eliminate brood within the hive for a short period of time. Without bee brood, the mites have nowhere to lay their eggs. During this time frame, without intervention, mite populations typically escalate exponentially. However, with no brood, the mites have no place to hide. The most dangerous time in a mites life is when she is not protected by the concealment of a brood cell.

Disrupting the brood cycle doesn't completely eliminate mites from the hives. Rather, it gives the bees an opportunity to knock their populations down to a manageable level. And with no brood, the bees have less mouths to feed. This equates to an increase in surplus honey. (Note: If a hive has a queen who is extremely productive, you may want to consider putting her in a nuc and seeing if she'll rebuild a colony that will overwinter.)

  1. Be vigilant about cutting out queen cells twice within 7-13 days. If you are planning to introduce a new queen to the hive, the bees will be more likely to accept her if they are unable to raise their own queen.

  2. After about 2 weeks, introduce a new mated queen. If you are planning to introduce a queen cell into the hive, you can do so after about 1 week. Ideally your hive should not be queenless for more than 18 days. After day 18 you run the risk of laying workers developing.

As you can see, disrupting the brood cycle of your bees (and your mites) isn't much more complicated than re-queening. If you are planning to requeen you hives anyway--or if you are hoping to implement a chemical-free method of mite control--I encourage you to consider the potential benefits of requeening at a time when brood cycles will be disrupted. Above all, I encourage you to take measures that will allow you to get away from managing mites and back to managing your bees.

1 comment:

Eater said...

Thanks for the info. I am a new beekeeper this year and trying to understand brood interruption to help control varroa mites. I understand the concept that brood nterruption will clean the brood of the mites, but what about the mites that are already attached to the bees? Won't those mites just repopulate the hive? Thank you for helping me understand this.