The Bee-Files

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Integrated Pest Management Varroa destructor in the Northeastern United States
Using Drone Brood Removal and Formic Acid


Chemical Control Methods

Available products
Currently, there are three products with Section 3 (General Use) registration available for controlling V. destructor. These are Apistan® (fluvalinate), Mite-Away II™ (formic acid) and Sucrocide™ (sucrose octonaote esters). In addition, CheckMite+® (coumaphos) and Api-Life VAR® (thymol, menthol and eucalyptus oil) have been granted Emergency Exemptions from registration (Section 18) by the US-EPA. These latter two products are only available in those states that have applied for and received Emergency Exemptions, which must be renewed each year.

Pesticide resistance
Resistance to the two major pesticides, Apistan® and CheckMite+®, is widespread. This is problematic because the resistance status of the mite population must be determined before treating a colony, rather than after. Presently, such a determination is difficult to obtain. You are referred to / or to for information on making this determination. There is no known resistance to formic acid (Mite-Away II™) at this time.

Established pesticide tolerances
Honey may contain 0.05 ppm fluvalinate and 0.1 ppm coumaphos. Beeswax may contain 100 ppm coumaphos. Remember! These are limits, not goals. Always think of pesticides as a means of last resort. Formic acid and sucrose octanoate esters are exempt from tolerance when used in accordance with label instructions. Menthol, thymol and eucalyptus oil (the active ingredients in Api-Life VAR®) are also exempt from tolerance, but their exempt status is subject to periodic renewal.

How to minimize pesticide residues in hive products
The use of pesticides inevitably results in residues in wax and honey. To minimize this problem, and to ensure that residues do not exceed established tolerances, use pesticides only when necessary and only in accordance with label instructions. Use separate hive bodies and combs for your brood chambers and honey supers and keep them separate. Never move combs from the brood nest into the honey supers. An easy way to keep these combs separate is to use deep hive bodies for brood chambers and mediums or shallows for honey supers. Apply pesticides in the brood chambers, never in the honey supers. These practices will greatly reduce the level of pesticide residues in the honey and the wax cappings.

General Recommendations for the Use Pesticides
  Do read and follow the product label.
Do follow all safety instructions, and wear all indicated personal protection equipment.
Do apply the proper amount of pesticide in the manner specified on the label.
Do remove the pesticide at the end of the specified treatment period.
Do dispose of used pesticides in the manner specified on the label.
Do follow any required withholding period. This is the minimum time that must elapse between removing a pesticide or antibiotic from a colony at the end of a legal treatment period and the addition of supers for honey production.
Do place pesticide strips in such a manner that they will remain in contact with the bees when the cluster contracts. This is particularly important in the fall. 
  Don’t leave pesticides in your colonies over the winter. It is illegal! It also increases the amount of time your combs are in contact with a pesticide, thereby increasing the risk of residues in hive products. It may also increase the chance of the mite population developing resistance to the pesticide.
  Don’t reuse products.
  Don’t use any chemical, pesticide or formulation of a chemical or pesticide to control V. destructor unless it is legal to do so in your state.
  Don’t use any pesticide in a manner inconsistent with its label.

Non-Chemical Methods of Control

Drone brood removal

Research: Mites are found most often on drone brood where they produce about twice as many offspring as on worker brood. Therefore, by removing capped drone brood from an infected colony, you remove a disproportionately large number of mites without affecting the worker population, and you remove those mites with the highest fecundity. Research at Dyce Laboratory for Honey Bee Studies at Cornell University has shown that the periodic removal of drone brood from a colony allows a beekeeper to skip the usual spring treatment, keep mite levels low throughout the summer and prevent fall collapse [Fig. 8]. It may also eliminate the need for a fall pesticide treatment. The only way to determine that is to estimate the pest density on a colony-by-colony basis after removing the fall honey crop.

Fig. 8: September mite-to-bee ratios in colonies with and without drone brood removal during the spring and summer in three apiaries.

Implementation: You will need four drone combs per colony to use this method. Drone foundation can be purchased from several supply houses. The foundation is wired into frames and drawn out by colonies. One piece plastic drone combs are also available. Use two deep hive bodies for brood chambers, and separate them from the honey supers with a queen excluder. Cull worker combs in the brood nest with more than 1-2 square inches of drone cells [Fig. 9]. Remember! The goal is to get the colony to consolidate all of its drone production in the removable drone combs.

Place two drone combs in the upper brood chamber, one or two combs in from each side. Visit your colony every 26-28 days, remove the drone combs [Fig. 10], and replace them with the drone combs that you removed on the previous replacement date. Place the combs of capped drone brood in a freezer, and keep them there until you are ready for your next exchange. Allow frozen drone combs to come to ambient temperature before placing them back in a colony. Be sure to visit your bees at least every 28 days to exchange combs because you don't want too many drones actually emerging in your hive. If a drone comb becomes filled with honey, you will need to substitute an empty drone comb and extract the honey before reusing it. In the north, you can exchange combs up to six times a season using a 28 day interval between exchanges. The more often you exchange combs, the more you will suppress the mite population. The drone brood removal method has no known deleterious effects on colonies, and honey production may be marginally increased.

Fig. 9: A worker comb with excess drone cells. Such a comb is best culled and replaced with a comb of 95-100% worker cells.
Fig. 10: Comb of capped drone brood being removed from colony.

Screen bottom boards

Research: Many studies have shown that mites fall off of bees at relatively high rates, even when no chemical treatment is present. Many of these mites are still alive and manage to reacquire a host. It is commonly believed that mite populations can be suppressed if these fallen mites can be removed from the colony before they reacquire a host. The screen bottom board allows mites that fall from bees to fall out of the hive. Since they cannot re-enter the hive, they cannot reacquire a host and they cannot contribute to the growth of the mite population.

Three years of research at Dyce Laboratory at Cornell University have shown that screen bottom boards have no effect on mite populations [Fig. 11]. The reason for this is unknown, but it may be because the fallen mites are sick or old and no longer able to reproduce. However, research on the efficacy of screen bottom boards is mixed. Two other studies have shown numerical benefits from screen bottom boards, but the advantages were not statistically significant. One study has demonstrated a small but statistically significant benefit. Screen bottom boards do not appear to damage colonies. If effective mite knockdown agents can be identified, screen bottom boards may play a more significant role in mite management.

Mite-resistant stock

There are two stocks of mite-resistant bees available. One is descended from Russian queens imported to the US. The other is known as SMR stock (for suppressing mite reproduction) that was developed from bees already present in the US. Both are the result of work conducted at the USDA-ARS Honey Bee Breeding, Genetics and Physiology Lab in Baton Rouge, LA. Performance of commercially available variants of these stocks is mixed. However, stock improvement is ongoing, and you are strongly encouraged to try them.

Swarm prevention
A swarm from one of your colonies will establish a nest within foraging distance of its parent colony. Invariably, swarms will have some mites, and since they do not receive treatment to control the mites, they will eventually collapse and die. As they do, the colonies in your apiary will likely rob them and return to their nests with a large number of mites. Attend your bees, especially in the spring, when swarming is likely, and take all necessary steps to prevent it. Remember! A colony that you allow to swarm not only has created a future threat to your bees; it will not produce nearly as much honey as if it had not swarmed.

One way to reduce the rate at which mite populations rebound after treatment is to keep apiaries isolated from each other. Increasing the distance between apiaries reduces the chance of re-infestation from nearby collapsing colonies. A separation of three miles will provide some protection, while a separation of five miles is better. Isolation is not practical where colony density is high, and isolation cannot guarantee that your bees will not be re-infested because there may be wild colonies in the area. However, this method should not be overlooked when selecting apiary sites.

Fig. 11: September mite-to-bee ratios in colonies with and without screen bottom boards during the spring and summer. No significant differences were found.
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© Copyright 2008, All rights reserved, Nicholas W. Calderone, Associate Professor,
Department of Entomology, Cornell University, Ithaca, NY 14853 


Updated July 2006
Web Site Design: Linda Fazzary