Drone Brood Removal

Varroa mites show a strong preference for drone brood and will seek out drone cells for the rearing of young.  Cells with drone brood are 8-10 times more attractive than worker cells.   Drone honey bees have a longer pupation period (developmental period when the cell is capped) than workers, and female mites can raise more offspring in drone cells than in worker cells.  This preference can be used advantageously to help reduce mite populations in a hive.  Since drone brood typically has more developing mites, the systematic removal of drone brood can be used to help keep mite populations below threshold levels.

In a normal colony the majority of mites (>60%) are found in brood cells, a fact which helps increase the effectiveness of brood removal techniques.  The selective removal of drone brood also minimizes the effects on worker populations. The basic approach involves the use of 4 frames of drone comb.  Two frames of drone comb (drone foundation is used to insure drone comb production) are placed in each hive.  At the same time any large patches of drone comb on other frames should be removed. The frames with the drone comb are left in the hive for 26-28 days, at which time the drone brood cells should be filled and capped.  The frames are then removed from the hive, the bees removed by brushing or shaking, and two other frames of empty drone comb are placed in the hive. The frames with the drone brood are placed in the freezer to kill the developing brood and mites.  At the end of a second 26-28 day period the second set of frames is removed and replaced with the frames from the freezer.  There is no need to clean the frames as the bees will remove the dead brood and clean the cells before reuse. The technique is fairly labor intensive, but the repetitive use of this procedure (at least 3-4 times per hive during spring and summer) can help keep mite populations at low levels.

   Old frame of empty drone comb and drone comb with some brood (late season).

The drone removal procedure can be simplified to reduce the need to handle multiple frames of drone comb each time the drone brood is removed by using medium or shallow frames in full-depth hive bodies in place of standard frames.  In the spring, replace two outer full-depth frames with shallow (or medium) frames.  As the colony expands, the bees will construct new drone comb on the bottom of the smaller frames. When the new comb contains capped drone brood, it can be cut off of the frame and discarded. The frame is then replaced and the bees allowed to construct additional comb.   The method works well in the spring of the year when colonies are actively expanding, but it may be difficult to get bees to draw and utilize drone comb later in the summer. 
Drone brood removal can help to keep mite populations at low levels, but there may also be drawbacks. Little is known about how the removal of drones may affect a colony or whether the energy utilized for new comb construction could negatively impact a colony. However, a study by Dr. Tom Seeley at Cornell has shown that colonies without drone comb produce more honey than colonies with drone comb (Apidologie, 2002, 33:75-86). Drone brood removal is also not an acceptable practice when producing queens.

Screen Bottom Boards

The use of screen bottom boards has been promoted as an effective management tool for the control of varroa mites. The idea is based on the fact that varroa mites often drop off of their honey bee hosts and fall to the bottom of the hive. A screen bottom (8 mesh hardware cloth) allows the mites to fall from the hive and prevents them from attaching to a new host.   The idea is simple and straightforward, but there has been some debate as to their actual effectiveness.  Some researchers have found that the use of screen bottom boards leads to significantly lower mite population levels in hives when compared to hives with solid bottoms (from 20-70% lower).  Other researchers found no significant differences in mite populations between hives with screen versus solid bottoms.  On the positive side, the use of screen bottom boards may help reduce the rate of mite population growth in new colonies, and provide for better ventilation of hives during the summer months, especially in warmer areas of the country.  Alternatively, screen bottoms may increase hive access for certain pests, and increase colony stress during the winter, if left in place.  In spite of the uncertainty, screen bottom boards are recommended for summer use as part of an integrated hive management approach.  For over-wintering hives, the screen bottom board can be replaced with a solid bottom board, or a thin sheet of plywood or similar material can be slide overtop of the screen to reduce colony exposure.

Queens and Requeening

Good queens are important to successful beekeeping, and the better the queen, the more productive the colony. This is particularly true with regard to queen lines that show resistance to diseases or mite parasites.  However, maintaining good productive queens has become more problematic in recent years. Beekeepers have expressed concerns over poor queen quality and high failure rates, indicating a need for careful monitoring of queen performance.  Beekeepers also need to consider the more frequent replacement of queens.  Poor queens should be replaced whenever they are discovered, but beekeepers may want to replace good queens on an annual basis, especially if they have had problems with winter survival and spring build-up.  Young queens are more productive, and colonies headed by young queens are less likely to swarm. Colonies headed by young queens may also have a better chance of surviving the winter.

The selection of good queen stock can play a key role in an integrated hive management approach.  Bees showing high degrees of hygienic behavior are more resistant to brood diseases and varroa mites, and the use of queens from selected hygienic lines can reduce problems with these diseases and parasites.  Several lines of hygienic bees, such as the Minnesota Hygienic, are available from queen breeders