The mite Varroa jacobsoni was first detected in the
United States in 1987 and likely arrived
via importation of uninspected bees into Florida. Since then its
spread throughout the United States has been rapid and fatal, especially to feral
colonies. Losses of feral bees have been estimated to be upwards of 95% in some
places while unaware beekeepers suffered losses of over 80% of their colonies forcing
some disappointed beekeepers out of the business. To understand why the Varroa mite is a serious problem and to prepare to fight the mite we must understand its lifecycle and biology.
The mature female Varroa mite will leave the brood cell from which she hatched and
attach herself to a worker bee by chewing though their exoskeleton and feeding on the
bees bodily fluids. The female then drops into an occupied brood cell and remains at
the bottom of the cell in the brood food or jelly. When that food supply is exhausted,
the mite will attach to the developing larvae and feed off its bodily fluids.
The mite then lays a number of eggs which hatch into male and female mites in
just 48 hours. Since the original female lays her eggs at 1 1/4 day intervals, the mites
hatch and mature over a period of time. The development to sexual maturity for the
mite takes 7 to 8 days for a female mite and 6 to 7 days for a male mite. Upon reaching
maturity, the mites breed and the male mites die. Female mites are able to leave the
capped cell when the bee emerges. The mites appear to favor parasitizing drone
bees which have a developmental cycle of 24 days rather than the normal 21 day cycle
for a worker bee.
The longer period in a capped cell allows more mites to reproduce
for each developing bee larva.
Bees that suffer paratization in the comb are either killed outright or hatch into
deformed or weakened bees. Bees parasitized as adults are poor fliers, are weaker and
generally live much shorter life spans than unaffected bees. One of the
indications of mite infection is the observation of bees walking on the ground
around a hive. Examination of these infected "crawling bees" may reveal
deformed wings due to the mites feeding interfering with the development
of the bees wings or damage to wing muscles. If you collect a few bees
in a small jar containing an inch of isopropyl (rubbing alcohol) alcohol
and swirl the jar a few times, the mites will come off and be visible
clinging to the sides of the jar. 
Needless to say, the bees will not
survive this test, but collection of several drones for examination can
reveal mite infestations easily. Examination of comb, may show small white
specks that are the droppings of the Varroa mite.
This site by an entomologist at West Virginia University discusses the effective control
of mites using essential oils
. A specific formula is suggested making use of honey or sugar as follows:
This good article on timing your treatments provides a well written explanation of when to apply acaracide strips.
The drone comb removal method is described here.
Current focus concerning the Varroa problem is on the issue of mite resistance to the single approved mite medication. The USDA recognizes Apistan as the only product which has been demonstrated as efective against mites. This oil based form of the chemical fluvanate is impregnated into strips to be placed in the hive at prescribed dosage levels of 1 strip per 5 frames of brood. The strips must be left in the hive for at least 42 days and no more than 56 days.
Treatment for mites must follow the medication recomendations. Practices such as keeping strips for re-use, or leaving them in for longer than the recomended period leads to a situation where mites are exposed to small, but non-lethal doses of medication. The lower levels of medication may kill the weak mites but any mite that might be resistant will survive to reproduce. This is the path by which mites become resistant.
An interesting history that documents the same situation in Italy can be read. It states in part:
"...When the situation improved with the introduction of apistan things seemed under control for a few years. However, many found the price of apistan too high and, finding another product with the same active ingredient (fluvinate) sold at a much lower price by the same manufacturer, started making the strips themselves, often mistaking the dosage. This, and the misuse of apistan itself lead to fluvinate resistant varroa which started killing hives all over again from 1992-3 onwards. "
Beekeepers must calculate into their profits, the cost of treating each hive properly. Additional financial cost and time cost must be considered so that medication strips are properly placed in each hive. Although this is expensive and labor intensive, the difference between spending the money up front and loosing an entire honey yard due to resistant mites makes the choice of proper treatments the only responcible choice.
An excellent article by Malcolm Sanford can be read here.
The loss of 66% of the bee colonies on Vancover Island demonstrated how severe the effects of the Varroa mite can be in areas which have never dealt with it. In Maryland, researchers suspect that 90% of wild bees may have already been wiped out by mites. The University of Massachusetts Extension Office has a good fact sheet on varroa.
