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Dr. Melody Wallace on Managing Varroa Mites in Honey Bees

5 Jan 2018 3:50 PM | Anonymous member (Administrator)

Some Long Beach Beekeepers may remember that way, way back, Dr. Melody Wallace visited from Cal Poly Pomona and had just gotten to the slide everyone was waiting for--the creepy, scary stuff, like pests, pathogens, and parasites--when we cut her off.

Dr. Melody Wallace of Cal Poly Pomona takes questions after her presentation on "Management of Varroa Mites in Honey Bees."

Dr. Melody Wallace of Cal Poly Pomona takes questions after her presentation on "Management of Varroa Mites in Honey Bees." Photo by Jacob Dickinson.

Or maybe she brought her presentation to an abrupt halt after foreshadowing the hair-raising material we'd get if we invited her back.

Let's just say that's what happened.

In any event, Dr. Wallace did come back, for our November 4 meeting, to thrill and chill with Management of Varroa Mites in Honey Bees.

The modern beekeeper's nemesis: Varroa destructor.

Let's remind ourselves how Varroa mites can be a problem. They weaken individual bees by parasitizing them. But there's more! They are vectors for a couple of dozen viruses that affect bees, like deformed wing virus. Thus, managing Varroa in honey bees can be critical.

My notes are as patchy as the shot brood Varroa mites can cause. (In fairness to the mites, Dr. Wallace told us that viral, bacterial, and fungal diseases can also cause shot brood.) Have I missed something good? Please add your comments! But here's some of what I got:

Measuring the Infestation

A reality check: all colonies have mites. It's a question of degree. What I get from this is: Don't lie awake at night feeling like an inadequate beekeeper if you find mites in a hive. What separates adequate beekeepers from inadequate ones is not whether mites can be found in the hive, but how the beekeeper responds!

How would you measure the problem in the first place? Dr. Wallace reviewed several diagnostic tools:

  • sticky boards
  • drone brood inspection
  • sugar roll
  • alcohol or soapy water wash

Sticky boards are easy to use and non-invasive, but Dr. Wallace believes them to be very inaccurate.

Drone brood inspection depends on having plenty of (disposable) drones. If you use this method, 10% infestation is a good treatment threshold.

The sugar roll is less destructive. I like to think that when bees covered with confectioner's sugar, like little white ghosts, are poured back in the hive, their sisters have a great time cleaning them up. But your mite count can vary, depending on the technique of shaking or rolling the bees. If you're testing several hives and have help, the same person should do the shaking for each hive. This approach will give more consistent results. (Most of us wouldn't think of this, since we work solo and take care of small numbers of hives.) Test about 300 bees: one measuring cup full is close. The treatment threshold is three mites per 100 bees, or 3%. This means nine mites from your one-cup sample.

You'll get the most accurate results from an alcohol or soapy water "wash." The downside is that this kills the bees in your sample. On the other hand, Dr. Wallace reminded us that 300 is only a fraction of a laying queen's daily production. A healthy hive will replace 300 bees in short order.

Dealing with the Infestation

Your mite count is over the treatment threshold. Now what?

Screened bottom boards are the low-tech approach. If a mite ever loses its grip, then down, down it will plunge, through the screen, to a mysterious, hostile jungle it's not equipped to deal with. But first it has to let go and fall. Dr. Wallace is not convinced these bottom boards have much effect on mites.

In general, beekeepers use fumigants to combat Varroa mites. Dr. Wallace pointed out that "natural" fumigants have their own hazards, so it's important to read the instructions.

Formic acid (used in Mite-Away) is popular. It's used occasionally in the Cal Poly Pomona apiary. Oxalic acid is also used, elsewhere, but is illegal in California. Both acids work well for a quick mite kill in the fall.

Amitraz (found in Apivar) works well, but more slowly.

Mites have developed resistance to coumaphos and fluvinate. Products containing these (for example, CheckMite and Apistan, respectively) are simply a waste of money.

It's a good guess that these chemicals build up in beeswax.

What About our Africanized Bees?

Dr. Melody Wallace of Cal Poly Pomona takes questions after her presentation on "Management of Varroa Mites in Honey Bees."

Dr. Melody Wallace of Cal Poly Pomona takes questions after her presentation on "Management of Varroa Mites in Honey Bees." Photo by Jacob Dickinson.

Most of us work with feral bees, which we assume are Africanized. Dr. Wallace gave us an excuse to feel smug, when she said that Varroa does not impact them as much. She mentioned several reasons for this:

  • grooming behavior
  • hygienic behavior (e.g. removing infected pupae from the hive)
  • 10-13 hours shorter pupation (compromising pupae as Varroa hosts)
  • more frequent swarms

Dr. Wallace left us with a thought about mite treatment: If we kill mites too thoroughly, we don't give bees a chance to develop resistance or tolerance.

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