Varroa Mites: Know Them to Control Them

Dennis R. Ring, Wilson, Gary K.

The key to controlling pests is having a complete knowledge of their life history, biology, and preferences. The more information you have about an organism the more likely it is that a weakness can be found. Varroa mites almost wiped out the entire population of wild honey bees in the United States; nearly 99 percent of the feral colonies were destroyed in some areas. The colonies that survived are being studied to see what traits allowed them to resist invasion by the varroa mites. Research stations are busy identifying, isolating and incorporating these traits into the general population. 

Varroa mites are ectoparasites, meaning they attach themselves to the outside of the honey bees to feed. They are reddish brown, oval and flattened in shape, which allows them to slide between the bee’s abdominal segments to feed. They do not permanently attach themselves to the bees and about 40 percent of the mites will at sometime fall to the bottom board of the hive. Normally they will wait there for a passing bee to acquire a new host, or will crawl up to four inches to reach a cluster of bees.

Screened bottom boards are a wooden frame covered with a #8 mesh screen. When the mites fall through the screen and are separated from the bees by more than two inches, they cannot sense the bees presence. Falling through the screen to the ground they will starve while waiting for a bee to come close enough to reattach. Screened bottom boards cut down on excessive heat and moisture. The bees can then use the energy normally expended fanning to ventilate the hive for other purposes. In some instances the bottom board is covered with vegetable oil or Tanglefoot and covered with the #8 mesh screen to trap the fallen mites for monitoring purposes or to remove them from the colony.

The sugar dusting technique was developed to enhance this mite fall. Varroa mites have an epodium or sticky pad on their feet that helps them adhere to the bee’s body; therefore, a thin film of fine powdered sugar dusted onto their bodies causes them to lose their hold on their hosts. The powdered sugar also stimulates the bee’s grooming behavior, they start cleaning themselves and each other which dislodges some of the mites. The mites cease feeding and release their hold on the bees to groom themselves.

Another chink-in-the-armor of the varroa mite is its preference for immature drones as opposed to feeding on immature worker bees. Honey bees mature within closed and caped waxed cells within the colony called brood chambers. Drones are larger and take longer to mature than the worker bees. This increases the survival rate of mites reared on drone brood. The queen can be encouraged to lay primarily drone brood by inserting a frame of drone comb into the hive. Once the brood in capped, the brood is placed in a freezer to kill the drones and mites. After the comb is well frozen, it can be removed and allowed to thaw. A capping scratcher is used to open the caps, and the brood is returned to the colony. The bees will remove the dead varroa mites and drones. This technique is labor intensive, but greatly reduces the varroa mite population.

Eradication of the varroa mite is not possible at this time. The aim is to use management techniques that reduce mite populations within the colony and do not adversely affect honey production or the health of the colony.
8/30/2011 12:02:21 AM
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