Varroa destructor

With a name like Varroa destructor you would expect the organism to be a problem causer, and it is. This mite virtually single handedly wiped out all feral honey bee colonies in many areas of the United States. These small (0.06 inches wide) mites feed on both adult bees and developing honey bee larvae. Adult mites lay eggs in the cells of the developing bee larva resulting in the death, deforming or seemingly no visible affect on the larva. After the bee matures the mites will also ride the adults feeding on the hemolymph. The mites also serve as transmitters of several virsuses that may kill the bees or compromise their immune systems.
Economic thresholds for mite infestations have been set for different sampling methods. If 10 mites are found on 200 bees by the sugar shake method control measures need to be taken. The sticky board method measures mites that fall to the bottom of the colony and become suck there, the boards are removed after 24 hours and the mites are counted. Colony size will then determine if the number of captured mites requires control measures be taken when counts exceed 60 to 190 mites.
Much work has been done on control measures and new alternatives are now available. Pesticide strips hung between the wax combs have provided high levels of control, but in some circumstances the mites are becoming resistant. Mechanical control measures do not use chemicals and may not be as effective in ruducing mite numbers but they do not use chemicals to control the mites. Screened bottom boards are benefical in reducing numbers of mites within the colony, but are not a stand alone treatment. Using drone-brood as a trap crop can dramatically reduce mite populations. Mites prefer feeding on the larger drone larva, and special combs with drone sized cells may be inserted within the hive then removed before the mites emerge. Covering the adult bees with powdered sugar can cause mites to loose their grip and fall off their host.
To me the most exciting advances are in honey bee genetics. Particular strains of honey bees are more tolerant to the mite because of a different behavior or physiological trait. Russian bees have been exposed to the mite for a number of generations and are more than twice as tolerant of the mites as the typical U.S. strains. Queens are being selected that show high levels of hygienic behavior toward varroa-parasitized pupae. The bees bred for brood-nest cleanliness significantly reduce the need for control methods.
Biopesticides are being registered for the control of the varroa mite. These naturally occuring organisms or their by-products are showing control efficacy equal to conventional chemical controls. One product uses a combination of essential oils within a vermiculite tablet to treat both varroa and trachael mites. Another is derived from tobacco plants and is sprayed on the adults as they emerge from the brood comb. Formic acid has been used by beekeepers in Canada and Europe for years to control mites during cooler weather (under 79 degrees) and when honey isn't flowing. Care must be taken with smaller hives, lest the bees be overwhelmed by the fumes.
Synthetic insecticides are still capable of giving up to 100% control of the varroa mites, but continual use can lead to resistance. State Departments of Agriculture have approved lists of products that may be safely used within the hives and only these should be used.