Mites in Package Bees - Playing with Randy's Varroa Model

April 27, 2018

First off... Thank you to Wayne Griffith for this picture, which inspired me to write a post about mites:

 

See those little dark specks? Let's take a closer look:

 

 

Yes, that ugly little critter is a Varroa Mite - a dead one. Wayne treated his package with oxalic acid vapor before installing it. In all, 24 mites dropped with the treatment. Oxalic Acid is a great treatment for packages because it kills phoretic mites - mites on bees instead of in brood, which there is none of in a package. A mite drop of 24 from OAV treatment actually isn't bad at all. Oxalic Acid kills about 95% of phoretic mites, meaning there were only about 25 mites in a package of 10,000 bees, or 0.25%.

 

So what would happen to Wayne's mites if he didn't treat? Well, here's a perfect opportunity to play around with Randy Oliver's Mite Model, which you can read about, download, and play with yourself -->HERE<--. The Mite Model simulates what will happen to Varroa population over time.

 

If we plug in some numbers - 26 mites on April 1st and an Oxalic Vapor treatment,  - and assume Wayne won't do any further treatments (bad assumption - Wayne already has the equipment and he's going to be a great beekeeper and do mite counts regularly... right, Wayne?), here's the output of the model:

 

 

The blue numbers represent the number of varroa per 300 bees. The red region represents the point at which the bee population collapses due to mite/viral load. So if Wayne doesn't do another treatment later in the season, his hive will probably collapse sometime in October. 

 

So how much good did treating the package actually do? Well, we can remove the treatment from the model and see the difference:

 

 

Not much of a difference. Why is that? Well, take a look at the other curves on the graph. Mites kill a hive when more than about 30% of the brood cells have mites in them. So during massive bee population buildup - Spring and Summer - the mite population doesn't grow fast enough to overwhelm the hive. But when the summer dearth hits and the queen lays fewer eggs due to the availability of resources, the mites have a chance to get a foothold, and the population quickly gets out of hand. 

 

If Wayne consistently does mite counts, and does an OA treatment whenever the count exceeds 1%, or 3 mites per 1/2 cup of bees, the curve will look like this:

 

Zero mites going into Winter, and healthy bees from consistently low mite counts throughout the year. That's what we want.

 

So what's the moral of this story? What can we do to make sure our new packages stay healthy?

 

- Feed your bees in Spring to ensure a good, strong population buildup.

 

- Feed them again (syrup and pollen substitute) during the dearth. This can reduce the brood production dropoff, and help raise big fat winter bees.

 

- Do mite counts once a month with an alcohol wash or sugar shake

 

- Treat any time the mite count is over 3 mites per 300 bees.

 

If we all commit to staying on top of the mite situation in our hives, we have a much better chance to get our bees through the winter! 

 

 

 

 

 

 

 

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