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Treating Honey Bee Hives for Varroa Infestation
with Oxalic Acid Evaporation
with records of subsequent Mite Drops

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On October 13th, 2011, twenty-five hives at Swalwell Alberta (5133'39.64"N  11318'52.45"W) were treated with oxalic acid vapour (OAV) using a Cowan power evaporator unit (left).  An amount of around four grams of the dihydrate per hive was administered.   Click here for a bird's-eye view of the location (requires Google Earth).

Fogging Beehives with Oxalic Vapour to Control Varroa mites, also variously known as sublimation and oxalic vapour treatmentThe 25 hives were treated again on November 10, 2011 using the same method.

On November 28 and 29, the oxalic vapour treatment was repeated, but a Heilyser setup and roughly 3g per hive were used this time.  Also, this treatment was done twice due to some technical problems which resulted in under-dosing some hives the first time.

On December 6 a fourth oxalic vapour treatment was made using two Heilyser units per hive (right) and a total of about 3 to 4 grams of the dihydrate per hive. 

A final treatment was made on December 23, 2011.  See below for details.

All hives are in EPS boxes, three and four storeys high, with plenty of feed.  They are a mix of overwintered hives and splits made from them over the summer.  The yard includes some B.C. stock, some California stock, and some Saskatraz offspring.

Six of the twenty-five hives were on special floors with screens above solid drop boards and were monitored daily for mite drops for the first 92 days.  After that time, drops were taken roughly every week and the counted mite number was divided by the actual days lapsed since the last count to estimate a daily drop.  In most cases, by then the drops were fractions of one mite per day and very often zero over the week.

On December 23 all hives were given a final treatment with oxalic vapour as previously mentioned, except that two of the six test hives received two strips of Apivar instead of OA treatment. This was intended as a 'finishing treatment', to show if any mites remained and to assist in assessing an efficacy for the earlier OA treatments.  Apivar is known to be roughly 90% effective in Alberta at present, although little is known about its efficacy in freezing weather.

Note: In addition to counting the mites dropping daily, observations were made as to the maturity of the mites counted, and immature mites were tabulated separately.  Absence of emerging brood and the beginning of broodlessness was inferred by noting the point where immature mites ceased to be observed in the daily drops.  This point was quite distinct. 

However, looking for immature mites in the drops was not a useful method for inferring resumption of brood rearing since the method requires a significant level of mite reproduction and also only shows emergence of mites, not the beginning of brood rearing which would have to commence at least twenty-one days previous to emergence.   In January, several square inches of sealed brood were noted in one hive, but due to the very low level of mites in the hive, no evidence was seen in the drops.  This is shown in the file, but not yet in the charts on these pages.

The background details and my thoughts can be found at http://www.honeybeeworld.com/diary/ beginning around October 12, 2011.  I started off pretty casually, thinking I was not seeing mites and wondering why, then looking more closely and improving my observation methods.  It has been a learning experience.

Initial counts were more casual than later counts, and some mites may have been missed in early counts.  The discussion in the diary documents the difference in counts achieved using extra light an magnification and those taken with the naked eye with or without reading glasses.  It is significant.

This page contains screen shots of the most recent report on the oxalic acid treatments and resulting mite drop counts, with the full-sized graphic images of the ongoing results.

The current raw MS Excel 2010 working data and the original charts which are reproduced on this page can be found here for download. (~200 KB)

Other file formats may be available on request for anyone wishing to work on further analysis or criticism.

Discussion and feedback takes place in the honeybeeworld forum and sometimes on BEE-L.org.  Please register and participate at either or both sites.

Please feel free to comment to me there or privately and ask questions or report errors.

Typical shots of the clusters in the test hives as at January 9, 2012
The plastic pillows were in close contact with the frames in the two left hives previous to pulling them back to take a peek,
so the bees are seen between the top bars and not on top.  The third shot is of a top box where the cluster is still down below.

The following screen shots are from the Excel 2010 file I use to compile and analyse the data. 

The screen shots below are provided for those who do not have Excel or who are just browsing, however downloading the the Excel 2010 file will provide much better resolution and more viewing possibilities. 

Note that the file is changed when I update it, so re-downloading is necessary periodically.

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Above is a chart that shows the average of all six hives under observation. 
Note that the red line uses the left Y-axis and the blue and green use the right Y-axis.

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Above is the same chart plotted logarithmically to enhance the smaller values and the trend.

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Each of the six hives is shown individually below in two separate views to illustrate the wide range of behaviours.

   
 
The charts above all use the same scale on the right and left axes and are thus
directly comparable
as to magnitudes of daily and total drops.

These same charts above have had the axes adjusted arbitrarily so that each plot
reaches roughly full scale and the plots are therefore not directly comparable.
The purpose of these latter charts is to reveal patterns of response. 
The same charts are repeated individually below.

 

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Individual charts from the right panel are repeated below. Note: Each is on a different scale.

Note: these charts below were up to date on Jan 12, 2011, but I am not updating them daily as I have been with the ones above. 
 It is too much work.  Nothing much has changed since then

The latest data, however are available on six separate sheets on the Excel 2010 file.
If you don't have Excel 2010, Write me for an alternate format.

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Young Mites /Total Mites

Day

Hive Number

1

2

3

4

5

6

This table shows the ratio of immature and young (soft, light-coloured) mites to the total mite drop. 

Colours are added for visual clarity. 

I did not think to tabulate this data until well after the beginning of the observations.

The presence of young mites indicates the presence of emerging brood, but only if there is a significant varroa population in brood.

Efficacy of oxalic treatments is greatly reduced when brood is present since as many as 2/3 of the mites are protected by cappings.

15

Oct 26

2/3

2/19

8/16

20/39

8/21

1/12

16

Oct 29

0/6

0/11

-

5/22

12/27

0/13

17

Oct 30

0/6

4/16

8/21

6/18

6/22

4/18

18

Oct 31

0/10

0/28

22/42

14/30

30/91

1/13

19

Nov 1

0/5

0/9

12/24

7/22

18/31

1/4

20

Nov 2

0/3

0/5

14/27

11/22

3/10

0/1

21

Nov 3

0/2

0/1

6/11

11/22

5/9

0/6

22

Nov 4

 0/2

0/9

4/15

20/37

8/23

0/9

23

Nov 5

0/2

0/6

3/16

12/25

0/1

0/2

24

Nov 6

0/3

0/1

1/5

8/19

0/2

0/5

25

Nov 7

0/0

0/1

0/5

21/40

0/2

0/2

26

Nov 8

0/3

1/3

0/3

5/16

0/2

0/2

27

Nov 9

0/5

2/11

11/25

6/49

0/3

0/10

0

Nov 10

0/4

0/4

9/27

6/22

0/1

0/4

1

Nov 11

0/46

2/8

62/164

3/48

0/4

0/20

2

Nov 12

2/131

0/28

34/404

4/190

0/7

2/85

3

Nov 13

0/114

0/47

10/293

0/94

0/9

0/78

4

Nov 14

0/56

1/51

23/365

0/150

0/8

0/65

5

Nov 15

0/49

0/90

6/270

0/128

0/13

0/63

6

Nov 16

0/16

0/42

6/185

0/71

0/5

0/46

7

Nov 17

0/9

0/45

8/168

0/70

0/6

0/26

8

Nov 18

0/3

0/22

2/73

0/66

0/3

0/12

9

Nov 19

0/4

1/27

2/70

0/32

0/3

0/15

10

Nov 20

0/3

0/11

3/58

0/18

0/2

0/8

11

Nov 21

0/1

0/7

3/36

0/18

0/1

0/6

12

Nov 22

0/1

0/28

0/34

0/7

0/0

0/9

13

Nov 23

0/3

0/49

3/64

0/23

0/64

0/12

14

Nov 24

0/9

0/30

2/80

0/52

0/0

0/16

15

Nov 25

0/1

0/15

0/24

0/38

0/0

0/4

16

Nov 26

0/1

0/21

0/41

0/22

0/2

0/13

17

Nov 27

0/0

0/10

0/27

0/6

0/1

0/4

0

Nov 28

0/12

0/29

0/47

0/24

0/2

0/6

1

Nov 29

0/1

0/12

0/21

0/20

0/1

0/8

No further immature mites are being seen after November 25
 

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Daily Weather Data for Treatment Period
From Environment Canada

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