Just to clear up a few errors, the European honey bee has only been parasitized for a number of decades, not millions of years. Therefore, it is hardly a surprise that they had no adequate defense mechanisms and only recently have efforts to select for resistance begun to bear fruit. Apis cerana, on the other hand, seems far better at keeping mite levels down. In the following excerpts, the origins of the association were traced, and the possibility of breeding mite resistance was proposed in 1986, less than thirty years ago. I think the idea that Asian bees can remove mites through the hole in the capping is wrong. The reason for the hole is not clear, but they certainly can't gain access to mites through it.

> It was not until the early 1960s, when it was discovered in the Philippines, that Varroa was recognized as a parasite of A. mellifera. A. mellifera had been imported into the Philippines; it became contaminated through close contact with A. cerana, perhaps through mutual robbing or the efforts of beekeepers to strengthen their A. mellifera colonies by giving them sealed A. cerana brood, which has been done in other areas of Asia. All introduced A. mellifera colonies, though they were good producers initially, succumbed to the Asian mites. A small but developing beekeeping industry of about one thousand colonies of A. mellifera in the Philippines was eliminated by varroa in a period of about 12 to 15 years.

> It is not clear when varroa first moved to A. mellifera in the USSR, but the mites were observed on A. cerana in far-eastern USSR in 1952. In 1965 widespread varroa infestation of A. mellifera colonies in western USSR was reported, with as many as 5,000 mites per colony and up to 70% of the brood infested. In 1971 an estimated 55,000 colonies were lost to the mite in the USSR. Untreated colonies die within 3-4 years of discovery of the mites, and the highest death rate of colonies occurs during the winter. By 1967, varroa was reported from Bulgaria, apparently imported with queens from the Balkans. In Bulgaria, there was up to 100% mortality in apiaries 3-4 years after the discovery of varroa mites.

MITE PESTS OF HONEY BEES
David De Jong, Roger A. Morse, and George C Eickwort 
Department of Entomology, Cornell University, Ithaca, New York 14853
Ann. Rev. EntomoL 1982. 27:229-52 

> A behavioral and physiological resistance mechanism of the Asian honey bee (Apis ceruna) to an ectoparasitic mite, Varroa jacobsoni, which causes severe damage to the European honey bee (Apis mellifera) in the beekeeping industry worldwide, is reported here for the first time. Parasitism by the mite induced Asian worker bees to perform a series of cleaning behaviors that effectively removed the mites from the bodies of the adult host bees. The mites were subsequently killed and removed from the bee hives in a few seconds to a few minutes. 

> The grooming behavior consists of self-cleaning, grooming dance, nestmate cleaning, and group cleaning. Worker bees can also rapidly and effectively remove the mites from the brood. The European bee showed cleaning behavior at low frequency and generally failed to remove the mites from both the adult bees and the brood. Nevertheless, the European bees do demonstrate such ability at lower frequency and success, hence, it may still open the possibility of selecting European bees which have higher capability of cleaning behavior, and later be used in breeding a mite-resistant line of European bees. 

The Resistance Mechanism of the Asian Honey Bee, Apis cerana Fabr., to an Ectoparasitic Mite, Varroa jacobsoni Oudemans
YING-SHIN PENG, et al
JOURNAL OF INVERTEBRATE PATHOLOGY 49, 54-60 (1987)

> In Apis cerana the mite reproduces only on the less cared-for male brood, as most infested worker cells are detected by worker bees and eliminated from the hive; Asian bees engage in mutual grooming and even remove mites from colonies. European bees do not undertake systematic cleaning, so once established in a colony the parasite population explodes by using all the available brood.

Behavioral attributes and parental care of Varroa mites parasitizing honeybee brood
Gerard Donze
Behav Ecol Sociobiol (1994) 34:305-319

> Occasionally, workers of A. cerana remove mite-infested pupae from capped drone brood, but more often they plug the pore of the drone cap as a defense against varroa mites and other diseases of drone brood. Drone caps of A. mellifera do not have central pores and are softer than those of A. cerana, which makes them more vulnerable to hygienic inspections by worker bees.

Effect of Brood Type on Varroa-Sensitive Hygiene by Worker Honey Bees (Hymenoptera: Apidae)
Jeffrey W. Harris
Annals of the Entomological Society of America Nov 2008

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