APIS Volume 3, Number 9, September 1985

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In this issue

• Upward Ventilation--Chalkbrood Connection?
• Wax Moth Control--Alternatives to Chemicals?

UPWARD VENTILATION

In the temperate areas of the United States, wintering honey bees is a constant problem. In the attempt to successfully winter their bees, beekeepers have tried a variety of techniques from wrapping colonies in hay, straw tar paper or foam insulation to wintering indoors in cellars or especially constructed buildings. For a long time collective wisdom deemed that it was of utmost importance to insulate the beehive against cold. This no doubt was influenced by those who thought bees were attempting to warm the interior of their hive as human beings did their houses. This is not the case. The bees only attempt to warm a discrete cluster of individuals within the hive. Insulating practices often brought on other problems; especially vexing was that the air trapped inside a colony by insulation was full of moisture.

Experience and research now indicate that moisture-laden air is more detrimental to honey bee colonies in winter than cold temperatures. In colder reaches of the colony, the moisture can condense and may even fall back onto the insulating layer of bees surrounding the cluster, producing an icy ball of bees. Therefore, conventional wisdom now dictates that insulation is not as important as venting excess moisture.

Upward ventilation and the use of an upper entrance have recently been discussed by Mr. G.W. Hayes, "Queen Excluder or Honey Excluder?," American Bee Journal, vol. 125, August, 1985. Although the title suggests that queen excluder use is emphasized, Mr. Hayes also develops a case for upper entrances, and by implication upper ventilation as well. He concludes his article with:

"We as beekeepers are constantly barraged with information about how beneficial ventilation and moisture removal is in over-wintered colonies. The upper entrance is always suggested as a method to accomplish this in winter and in very warm humid conditions during the summer. There have been many, many articles and whole sections of books written on the upper entrance theme...Perhaps we as beekeepers should be more flexible and look more closely at the Upper Entrance as a more efficient year-around option."

The need for adequate ventilation is also well documented during nectar flows. Some beekeepers routinely provide upper entrances for bees by proping up covers or even providing elevation blocks at four corners between supers. These practices expose the surfaces of the combs to the large volume of air needed to reduce excess moisture in nectar. Care in ventilating hives is always tempered by the possibility of robbing; careful observation and judgement by the beekeeper must always be exercised to provide for maximum ventilation with minimum exposure to robbers. The stronger a colony of bees, the less possibility robbing will take place.

Florida does not have severe winters when judged by the same standards as those in the midwestern United States, nor does it have the long, intense nectar flows often found in that region. But the State can be extremely humid during much of the year, and so maximum upward ventilation is also required to evaporate excess moisture during nectar flows.

In recent times, large outbreaks of chalkbrood have been reported by beekeepers in Florida. The disease is characterized by the brood turning into hard white chalky looking "mummies." It probably exists in most colonies on a year-around basis (is endemic) and, like nosema, becomes epidemic when conditions for its survival are optimum. There is no chemical control for chalkbrood. It appears that so-called "good" management technique will reduce its incidence. Generally this calls for reduction of stress in a colony and the use of stock that might be resistant (that is adept at removing the chalkbrood mummies from cells to allow further brood production).

Chalkbrood is caused by a fungus that appears to flourish in humid conditions. Does upward ventilation play a role in controlling the disease? Are Florida colonies ventilated properly to aid in reduction of chalkbrood buildup? Many may not be. In the spring of the year when chalkbrood is epidemic, there is quite a lot of stress on a colony. Cool morning moisture-laden air can easily "drain" into the bottom entrances of colonies. As the colony warms up during the day, upward convective ventilation in a properly ventilated colony should dissipate the moisture. The longer the moisture is trapped inside the colony, the greater the chances of it contributing to stress on a colony and to fungal (chalkbrood) development. Conversations at this year's Institute indicated that beekeepers whose colonies had an abundance of upward ventilation had fewer chalkbrood problems. Perhaps the time has come for the Florida beekeeper, like his/her midwestern counterpart, to pay greater attention to the role of upward ventilation in a colony.

WAX MOTH CONTROL

There was discussion at this year's Institute on wax moth control in stored supers, generally accomplished in the past by chemical fumigation. The availability and suitability of these chemicals, however, is constantly in flux; they are expensive and often require special training to use (see last month's APIS on the Right To Know Law), and there is the ever present chance the chemicals might find their way into the honey.

Several chemical fumigants effectively used in the past are methyl bromide, ethylene dibromide (EDB) and paradichlorobenzene (PDB). Of these, only one, paradichlorobenzene appears to have any long-term future as a registered pesticide against wax moth. Unfortunately, it does not kill all stages of wax moth and will not clean up a severe case of moths already established. It remains only a preventative.

It is usually adviseable to buy any fumigants for beekeeping use from bee supply houses; this way full information on use of the substance in beekeeping is available. All pesticides must be labelled for use on stored comb; the LABLE IS THE LAW, and under no circumstances should a pesticide be used if it is not SPECIFIED on the label. Beeswax is similar in structure to many insecticides and often has an affinity for them. As a consequence EXTREME CAUTION should be excercised when using pesticides anywhere near a beekeeping operation. For further information on toxicity of pesticides, see Florida Cooperative Extension Circular 534, Protecting Honey Bees From Pesticides.

Alternatives to chemical fumigation have not been found to be practical in large-scale application. These include the use of hot and cold temperatures, and fumigating with carbon dioxide.

The following is a chart of temperatures required to kill all stages of wax moth using cold or heat treatment:Controlling Wax Moths with Temperature

Care should be taken when treating with cold because beeswax becomes brittle and breaks easily. Even more caution, however, is advised when heat-treating. The combs should only have very little honey, must be placed vertically in supers and the heat MUST be circulated to avoid hot spots which would melt the wax.

Fumigation with carbon dioxide (CO₂) is extremely dangerous, not because the chemical is inherently toxic, but because a user can be suffocated quite easily while using it. It is not recommended for the amateur! Fumigation for four hours at 98 percent concentration CO₂, 100 degrees F., and 50 percent relative humidity is required.

A relatively new product on the market called Certan® is also an alternative to fumigation. It is a particular strain of bacterial disease which attacks wax moth larvae, but has met with criticism because it is expensive to apply on a large scale. [Editor's Note 5/11/1997--Certan® has been withdrawn from the market and will not be reregistered.]

Some of the worst cases of wax moth damage occur in stacks of supers. This appears to be the ideal environment for the moth larvae which build up to large populations quickly. Ironically, experience with stored comb in many areas of the tropics reveals a smaller wax moth buildup than might be expected. The reason for this paradox is has to do with storage technology. The combs in these areas would also be destroyed quickly if stored in supers. However, when separated and suspended on racks under sheds and, thus, exposed to ventilation and light, the combs often suffer little damage. The environment caused by this storage technique apparently is not so conducive to wax moth buildup as when combs are stored in stacked supers.

I was informed at this year's Institute that one beekeeper who routinely stacks supers at right angles to each other so the corners are ventilated and lighted has reduced wax moth problems. Although not applicable to every beekeeper's style, this storage technology based on ventilation and lighting principles or some variation of it, is one alternative to chemical fumigation that might be explored in the constant search for adequate wax moth control in stored comb.

Sincerely,

Malcolm T. Sanford
Bldg 970, Box 110620
University of Florida
Gainesville, FL 32611-0620
Phone (352) 392-1801, Ext. 143 FAX: (352)-392-0190
http://www.ifas.ufl.edu/~entweb/apis/apis.htm
INTERNET Address: MTS@GNV.IFAS.UFL.EDU
©1985 M.T. Sanford "All Rights Reserved