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Varroa treatments with and without brood

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A lot of you use some treatment, (it doesn't really matter what for this discussion), and your mite drops don't change much afterwards and you assume you're not killing mites. So let's just look at some numbers

Independent of WHAT the treatment is, here is just a rough idea of what goes on. These are round numbers and probably underestimate the mites' reproduction and underestimate how many get groomed off by the bees.

Assuming treating every week and a treatment with 100% effectiveness on phoretic mites. If you assume that half the Varroa are in the cells and you have a total mite population of 32,000, and if we assume half the phoretic mites will go back in the cells and in one week, half of the mites in the cells will have one offspring each and emerge then the numbers look like this:

100%

Week

Phoretic

Capped

Killed

Reproduced

Emerged

Returned

1

16,000

16,000

16,000

8,000

16,000*

8,000

2

8,000

16,000

8,000

8,000

16,000

8,000

3

8,000

16,000

8,000

8,000

16,000

8,000

4

8,000

16,000

8,000

8,000

16,000

8,000

* half of the 16,000 plus 8,000 offspring

Capped is inside capped cells. Returned is the number that went back into cells and got capped.

Now let's Assume treating every week and 50% effectiveness on phoretic mites with all the other assumptions the same:

50%

Week

Phoretic

Capped

Killed

Reproduced

Emerged

Returned

1

16,000

16,000

8,000

8,000

16,000

12,000

2

12,000

20,000

6,000

10,000

20,000

13,000

3

13,000

23,000

6,500

11,500

23,000

14,750

4

14,750

26,250

7,375

13,125

26,250

16,813

Now let's Assume treating once every week with 50% effectiveness with no brood in the hive:

50%

No

Brood

Week

Phoretic

Capped

Killed

Reproduced

Emerged

Returned

1

32,000

N/A

16,000

N/A

N/A

N/A

2

16,000

N/A

8,000

N/A

N/A

N/A

3

8,000

N/A

4,000

N/A

N/A

N/A

4

4,000

N/A

2,000

N/A

N/A

N/A

Then of course there's 100% with no brood:

100%

No

Brood

Week

Phoretic

Capped

Killed

Reproduced

Emerged

Returned

1

32,000

N/A

32,000

N/A

N/A

N/A

2

N/A

N/A

N/A

N/A

N/A

N/A

3

N/A

N/A

N/A

N/A

N/A

N/A

4

N/A

N/A

N/A

N/A

N/A

N/A

And no treatment would look like this:

0%

Week

Phoretic

Capped

Killed

Reproduced

Emerged

Returned

1

16,000

16,000

N/A

8,000

16,000

16,000

2

16,000

24,000

N/A

12,000

24,000

20,000

3

20,000

32,000

N/A

16,000

32,000

26,000

4

26,000

42,000

N/A

21,000

42,000

34,000

A real mathematical model, of course, should take into account a lot of things including drifting, robbing, hygienic behavior (chewing out), grooming, time of year etc. I was just hoping to get the general principle across of what is happening when you treat.


Michael Bush

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Copyright 2006 by Michael Bush

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