If a product has a 96% efficacy rate in killing varroa, what does that really mean?

We’ve had a very good question from a Vita Bee Health product user.

“When you say there’s a 96.8% efficacy rate in killing varroa, what does that really mean? And what is the difference with the infestation rate?”

Paulo Mielgo, Vita Bee Health’s technical director gives the answer:

A treatment efficacy rate of 96.8% means that 96.8% of the mites that were in the colony during the treatment period were killed.

So, if there were 1,000 varroa mites in the colony before treatment, 968 would be found dead after treatment.

In contrast, the infestation rate is measured by an alcohol wash before and after treatment to count mite numbers. So, if there were 40,000 bees with an initial infestation rate of 2.5% (ie, 1,000 mites), a product with an efficacy rate of 96.8% would kill 968 mites of 1,000, leaving a post-treatment infestation rate of 0.08%.