MITE TREATMENT OBSERVATIONS

I have been watching the natural varroa mite fall from four hives using screened bottom boards with witness boards.  The main reason for doing this was to track the mite fall of two types of mite biter breeder queens I had purchased. One a standard Purdue Mite Biter (PMB) and the second a feral queen crossed with PMB drones.   Every day for the past two months I have pulled the witness boards on all four hives and recorded the number of live and dead mites dropped by each hive.   I wasn’t actually comparing apples to apples.  The two breeder queen hives were started in early June from nucs.  The other two hives were overwintered hives.  The overwintered hives had 3rd generation PMB queens.  Due to the difference in the hive populations and longer time period for the mite population to grow, one would expect the overwintered hives to drop more mites; which they did.  Mite drops have been recorded every day since June 27th. 

Witness board partially withdrawn.  It is fully withdrawn to allow easy counting of the mite drop. 

Just prior to applying mite treatments to the two overwintered hives I calculated the daily mite fall of each hive (based on a 7 day moving average). 

Hive A-1.8 mites per day   Feral breeder queen hive

Hive B-0.7 mites per day   PMB breeder queen hive

Hive C-2.4 mites per day   One of the two overwintered hives with 3rd gen PMB queen

Hive D- 11.3 mites per day   Strongest of the two overwintered hives with 3rd gen PMB queen

The mite fall has been slowly increasing for all hives as the summer has progressed.  This would be expected because the mites are continuously increasing in number as they reproduce.  I have previously read that mite drops of more than 10 to 12 per day indicate a hive in danger of a varroa caused crash. 

Formic acid treatments are known to be hard on queens.  Not wanting to risk my breeder queens at this time I skipped treating Hive A and B for now.    Hive C and D were treated with a full dose (2 pads=1 packet) of FormicPro on July 29th.   Here were the results 

In the first 24 hours after treatment Hive C dropped 59 mites and Hive D dropped greater than 200 mites.  Mite drop was its maximum on the first day after treatment and declined afterwards.  The mites dropping after treatment were all dead.  Prior to treatment it was a mix of live and dead mites.  Total drop for the 2 week FormicPro treatment period were 259 mites for Hive C and 443+ mites for Hive D.   

Here is a table showing the mite drop. 

Days after treatment	Hive A	Hive B	Hive C	Hive D
1	1	0	59	200+
2	1	3	27	174
3	2	2	16	30
4	1	0	17	17
5	0	3	17	2
6	1	0	20	0
7	0	1	15	6
8	0	1	16	2
9	0	2	10	1
10	0	1	25	3
11	4	3	19	4
12	1	1	13	2
13	2	5	3	1
14	1	1	2	1
TOTAL	14	23	259	443+

 The results of the treatments on Hive C and D show FormicPro does kill mites.  The initial mite kill is massive and then slowly tails off as the strength of the emitted formic acid vapor decreases and the number of mites declines.  A low level of mite drop will likely continue as the capped bee brood reaches maturity and emerges.  Along with the emerging bees come hopefully more dead mites, both ature and juvenile, from beneath the cappings.  The slightly elevated mite drop will probably continue for 3 weeks. 

One thing that is puzzling me is the relatively low mite drop from the overwintered hives with the 3rd generation PMB queens.  Are the genetics in the 3rd generation queened hives still having a negative effect on mite populations?   Based on the Scientific Beekeeping Varroa model I would have expected the mite drop to be in the thousands.  Just maybe these 3rd generation queens are contributing to my good winter survival.  

Hive D exhibited less mite resistant behavior than Hive C.  I plan on replacing Hive D’s queen with a queen from one of my breeder queens after removal of the honey supers.   

I also plan to do alcohol wash mite checks on all four hives for several reasons:  1) as a cross check on the sticky board results, 2) to verify the mite treatments effectively did their job of killing off the mites,  3) to verify the mite levels of the two breeder queen hives are really as low as indicated by the witness board counts.   I will report on these new test results when completed.

What was especially encouraging from this little exercise was that the two hives with Mite Biting breeder queens are not, to date, showing the sharp rise in mite counts that normally occur in August.  Their mite counts are remaining low; 1-2 mites/day on average; well below the 10 mite per day drop where treatment with miticides is recommended.   I will continue to track the mite drops of all four hives through October.  Normally mite levels shown by mite drop to sticky boards or by alcohol washes sharply rise in August through October as the hive’s bee population downsizes in preparation for winter.   The rise in mite counts isn’t because there are more mites; rather there are less bees and less brood cells for the mites to hide in.   Therefore, the probability of a bee or larvae getting damaged by a mite sharply rises.