Cedar: a control for varroa mites

Goals

This project aimed to test the effectiveness of cedar as a control of varroa. A destructive pest that depletes the strength of bees and increases hive mortality through disease, varroa is the most serious threat to bees and beekeepers worldwide. With varroa mites continuing to develop resistance to chemical controls, beekeepers are searching for a way to increase the odds of hives surviving through winter.

Begun in the spring of 2005 with thirty-six hives organized into three groups of twelve each, the project attempted to find out if cedar present in a hive will work to knock mites from bees onto a sticky board beneath the hive, where the mites perish. Many substances have been proven to knock mites from bees. To our knowledge, cedar has not been tested before. The use of a substance that requires little time per hive to control varroa would increase the economic viability of many beekeepers, particularly large sideline beekeepers and professional beekeepers.

Our Farm

O'Meara Family Farm is a diverse farm. We have a small grass-based dairy consisting of twenty-two dexter and dairy cross animals, eight of which calved in 2006. We sell eggs, dairy products, and honey from the farm. We have also sold a considerable amount of beef and pork in 2006. A small cheese facility is currently under construction on the farm.

The farm consists of fifty-seven acres, thirty of which are open. We log with oxen and sell firewood from the farm. A large amount of lumber and firewood from our farm is used to heat the house and to build barns on the property.
Approximately two acres on our farm are in garden, including fruit trees. We hay about three acres of our own land, close to the property lines. In 2005, we hayed about twenty-five acres off our farm, within the neighborhood. We have hayed approximately fifty acres on other farms in 2006.

We raise heritage breeds of ducks, geese, and chickens, which are rotated through the fields after cows. One recent addition to our operation was the purchase of a small band sawmill. We currently have one team of Dexter oxen, which we use extensively for harvesting wood. We have recently begun training a young team of calves as our next team of oxen.
Although the market for many products is quite different here in northern Maine than in Massachusetts, where we used to farm, we continue to consistently sell honey.
We are currently in the process of becoming certified organic.

The Project

In May of 2006 thirty-six hives were organized into three groups of twelve hives each: Groups A, B, and C. Each group contained four hives constructed from cedar-numbers 1-4 in each group. (These hives were constructed on the farm from wood harvested here and sawn on our sawmill, since cedar is prohibitively expensive.) Each group also contained four conventional hives that were treated with cedar chips- cedar shavings and chips were placed on the top bars of these hives- numbers 5-8 in each group. The other four hives in each group went untreated- they serve as the control for the experiment- numbers 9-12 in each group.
Sugar rolls were performed at the outset of the experiment to establish a base line of mite infestation. Sugar rolls were also taken once a month to monitor the mite population.

Mite counts were taken every two weeks using sticky boards beneath screened bottom boards to monitor mite populations throughout the season.
Hives were managed for maximum honey production throughout the 2006 season.

Results

Mite populations were low to nonexistent in all the hives when the experiment started. Although spring comes late to northern Maine, the hives built up quickly and were prepared to take advantage of major honey flows in late June and July.

The sticky traps and sugar rolls performed throughout the season showed a steady increase in mites in all hives.

Sugar rolls- The initial sugar roll showed no mites in all of the hives but three: hives 6A, 12A, and 9B showed one mite each. However, no mites were evident when a sampling of bees from the other hives were subjected to a standard sugar roll. Mite populations continued to increase throughout the summer- please see attached sugar roll tables.

Sticky traps- Initially, the sticky traps showed no mites. By July the first mites were showing up on the traps. By the fall, many hives were showing high populations of mites- both on the sticky boards and in sugar rolls. Although this situation would normally warrant the use of a chemical miticide, in the interests of the experiment, the hives were left untreated and prepared for winter. (Please see attached sticky trap tables.)

However, there was no easily identifiable pattern in the mite populations in cedar hives, hives treated with cedar shavings, or in the control hives.

The cedar hives in groups A and B did show higher levels of mites on the sticky traps than the control hives and the hives treated with cedar chips. Mite levels on the sticky traps in group C, however were comparable to those in the other hives in that group.

The sugar rolls showed that the mite populations were fairly constant throughout all hives. Because sugar rolls indicate the number of mites per a certain number of bees, they may indicate a more accurate picture of the mite populations in the hives. The sticky traps, in contrast, indicate the number of mites falling from the whole hive. A larger hive with more bees will have more mites on its sticky board, regardless of the treatment. A hive in serious decline will have fewer bees on its sticky trap relative to other hives, even if it does have a serious mite problem.

The elevated levels of mites on the sticky traps in groups A and B, in combination with the relatively similar number of mites showing up in sugar rolls in those same hives, does seem to indicate that perhaps the cedar hives were working to eliminate mites from the bees in hives 1A-4A and hives 1B-4B. The absence of those results in group C casts doubt on that conclusion.

The issue is further complicated by the fact that only one cedar hive from the entire experiment survived the winter of 2005-2006.

Survivability

Losses among the hives were quite high over the winter of 2005-2006. Although honey production was good and many of the hives were quite strong going into winter, mite populations were relatively high. Perhaps in combination with northern Maine's exceptionally long winters, the mite populations resulted in the failure of all hives but nine.

The following hives in each group perished during the summer:

Group A:
3A (queenless-8/14)
5A (bears-8/14)
9A (queenless-10/1)
10A (queenless-10/1)
Group B:
SB (bears-7/1)
9B (queenless-9/1)
Group C: none

The following hives survived the winter of 2005-2006 and produced well throughout the summer of2006:

Group A: 4A,6A, 12A
Group B: 6B, 10B
Group C: 5C,7C,9C, 12C

The hives that survived the winter had the following number of frames of bees per hive in April:

4A - 5 frames
6A - 4 frames
6B - 7 frames
10B - 8 frames
5C - 5 frames
7C - 6 frames
9C - 8 frames
12C - 9 frames

The following hives died in the fall or winter of 2005-2006. All of these hives were dead by February of 2006.

Group A: 1 A, 2 A, 7 A, 8 A, 11A
Group B: 1 B, 2B, 3B, 4B, 7B, 8B, 11 B, 12B
Group C: 1C, 2C, 3C, 4C, 6C, 8C, 10C, 11C

Survivability by treatment:

Cedar hives: 8%
Hives with cedar chips: 32%
Untreated hives: 32%

Unfortunately, only one hive constructed of cedar survived the winter. Although it is possible that the cedar had some adverse affect on the bees, high mite populations could also account for the high mortality. Of the control hives and those treated with cedar chips, an equal number of hives survived. This data indicates that cedar either has no affect or a negative affect on the survivability of honey bee hives.

Honey Production:

2005 was a good year for honey production. The hives produced well, despite the higher mite loads later in the year. Although most hives produced above average amounts of honey, again, we have not been able to find a pattern where any of the groups of hives produced more or less honey depending on their treatment.

Pounds of honey per hive:

Group A....Group B....Group C
1A - 35....IB - 38....1C - 25
2A - 30....2B - 40....2C - 37
3A - 0.....3B - 33....3C - 30
4A - 50....4B - 44....4C - 36
5A - 0.....5B - 0.....5C - 50
6A - 38....6B - 40....6C - 23
7A - 22....7B - 28....7C - 45
8A - 25....8B - 20....8C - 19
9A - 0.....9B - 0.....9C - 53
10A - 0....IOB - 34...10C - 37
11A - 30...11B - 45...11C - 21
12A - 58...12B - 27...12C - 57

Honey production by treatment— average pounds per hive:

Cedar hives: 33.1
Hives treated with cedar chips: 25.8
Untreated hives: 30.1

One management problem surfaced early - bears. We lost three hives to bears in June. We improved our electric fencing around the hives, which kept bears away for the rest of the season. Unfortunately, we were unable to locate three good locations that could be secured with a bearproof fence without spending a lot of money on new fencing. We ended up locating two of the groups of twelve on our farm, where they were watched closely. Group C was located at a farm about five miles west of our farm, secured with an electric fence, and watched over by a friend. All hives were returned to our home farm in October.

Other than high mite populations, the exceedingly wet fall in 2005 may have stressed hives to some extent. Our climate consists of a relatively short, though intense forage season for bees, followed by an exceptionally long winter. Although beekeeping is certainly successful in this climate, a combination of stresses on the bees may make overwintering losses high.

Although we have not as of yet been able to identify a pattern in the mite populations that indicates any solid benefit to using cedar hives for varroa control, we have seen other benefits to cedar hives. They are light, which is a considerable advantage when one person has to move many hives at night before the bears return. They are durable and rot-resistant; they require no paint.

The issue of survivability is a major concern that needs to be resolved before cedar hives could be recommended for either hobby or commercial beekeepers. Although there was some indication that the cedar hives were knocking mites from the bees, the fact that almost all of the cedar hives perished during the winter merits further study.

Cedar hives may be economically viable for beekeepers because of their positive qualitites, even if they do not help with varroa mites. However, because of the cost of cedar wood and labor, they would probably only make sense for hobby beekeepers, small sideline beekeepers, or for beekeepers who make their own hives and have a source of reasonably priced wood.

We have also come to the conclusion that cedar shavings or chips are difficult to apply in a consistent manner to a hive. Sawdust falls to the bottom of the hive too quickly and chips or shavings take up a bit too much room. The more practical application seems to be to simply construct the hive from cedar. Also, there was no indication that the cedar chips knocked the mites from the bees.

Overall, the results for this experiment were somewhat mixed. The data on mite populations in groups A and B indicates that cedar hives may show some promise as varroa control. Group C did not show the same promise. A serious problem with survivability of the cedar hives makes recommendation of cedar hives impossible based on the results of this experiment. Although cedar hives have positive qualities and may help in knocking varroa mites from bees, no definite recommendation can be made based on the experiences associated with our thirty-six hives over the past two years.