How Many Varroa Mites In The Hive?

The point of this article is to encourage beekeepers to carry out mite washes at some point in the season and treat colonies with oxalic acid every winter. I missed the winter treatment on an apiary last year, and the impact has been significant. Every mite alive in your hive on 1st January could turn into thirty mites by the end of June and a hundred by early September. It’s worth knocking them down when the bees are broodless. Once varroa mites take hold, the chances of damage by viruses such as deformed wing virus and chronic bee paralysis virus escalate.

Alcohol mite washes

I did a load of alcohol mite washes on 17th June at one apiary and was quite shocked by how many mites were in the hives. I thought that perhaps the reason was that when I did my winter oxalic acid treatments, there must have been some sealed brood. Then, when I got home and checked my records, it turned out that I had not done a winter treatment on that apiary. What a foolish walrus – what was I thinking? 

I have eight production hives at the site in question. The number of mites per half-cup of bees (300 bees) was as follows:

Apiary Two

The June 2021 mite washes were on 22nd June, almost exactly a year ago. Hive 16 was low in both years (same queen), and the ones that were poor last year were poor this year too. The bees in hive 16 are not especially defensive, and they seem to be doing well for honey. This could be a potential breeder queen next year.

Compare two hives

Let’s compare the history of a good hive (hive 16) with a bad one (hive 20).

Hive 16: 

22nd June 2021 mite wash was four mites from 300 bees (1.3%)

2nd September 2021, gave Thymovar treatment after removing honey

26th September 2021 gave Apivar strips

16th November 2021, removed Apivar strips

12th June 2022 mite wash was three mites from 300 bees (1%)

Hive 20:

22nd June 2021 mite wash was twelve mites from 300 bees (4%)

29th June 2021 treated with VarroMed trickle (1 of 3)

5th July 2021 treated with VarroMed trickle (2 of 3)

10th July 2021 treated with VarroMed trickle (3 of 3)

2nd September 2021, gave Thymovar treatment after removing honey

26th September 2021 gave Apivar strips

16th November 2021, removed Apivar strips

12th June 2022 mite wash was ten mites from 300 bees (3.3%)

I think that there is an element of varroa mite resistance in hive 16. If I’d treated hive 20 with oxalic acid when broodless in early December, the mite numbers now would be much lower – probably down to a 1% infestation or less.

When I went to do alcohol washes at an apiary that got treated with oxalic acid by sublimation (vaping), the situation was far healthier:

Apiary Three

The hives at this apiary were treated with OAV on 16th December 2021. When I did the ‘vaping’, the temperature was 12 deg C. If it had been very cold, I would have trickled the oxalic acid because the bees would have been in a tight cluster. The average mite count at Apiary Two was 7.75 mites per 300 bees (2.6%) and 2.2 (0.7%) at Apiary Three. This vast difference is magnified over time as the mites breed. The Randy Oliver varroa model shows that untreated, the colonies at Apiary Two have over 10,000 mites by early September, which is enough to finish them off. By contrast, Apiary Three colonies would have around 3,000 mites. 

Formic-Pro to the rescue

The hives at Apiary Two have received their Formic-Pro (formic acid) treatments, except for Hives 16 and 6, which didn’t need it. I have not used this before, and I never used MAQS either – I’ve heard too many stories about killed brood and queens. However, I’m delighted that such a product exists in this situation. They have high levels of varroa, and the honey supers are on – if I do nothing, they will die anyway. As I have plenty of queens, I can easily replace any that don’t survive the formic acid. I’m hopeful that, however good Formic-pro turns out to be, I won’t need it again because I’ll be doing the oxalic treatment in winter – on every apiary.