The honey bee tracheal mite (HBTM) (Acarapis woodi) has been a recognized problem by beekeepers since 1917 (Adam, 1968). Indeed, in 1922, the U.S. Honeybee Act (a Federal egulation) prohibited the importation of all life stages of honey bees into the U.S. primarily to keep this parasite out of the country. The HBTM was found in Mexico in 1980 (Wilson and Nunamaker, 1982). A National survey was conducted from 1980-82 to determine if the HBTM was in the U.S. By the end of the survey the HBTM had not been found in the United States (Shimanuki et al., 1983). However, the mites were found in Texas in 1984 (Delfinado-Baker, 1984) and must have reached S. Arizona as early as 1988 since several beekeepers in this area had unusually heavy over-winter losses the winter of 1989-90. One particular beekeeper, near Sierra Vista, AZ lost 30% of his 700 colony operation that winter and the next and it was determined that the colonies were severely infested with HBTM (Loper et al., 1992). Similar problems have been experienced all over the U.S. but in many locations, especially where winters are 3-4 months long (broodless periods for 1-2 months) the bees that have survived seem to have some genetic resistance. A process of natural selection or "survival of the fittest" has reduced the HBTM problem especially in somewhat isolated, non-migratory operations. One selected line of bees developed in S. Arizona, is generally mite-free except in colonies that superseded the previous spring or summer; then low levels of HBTM may be found in them during the winter.
It seems that in warmer climates where brood rearing is continuous, the constant production of new bees allows even "susceptible" colonies to survive although no one completely understands the dynamics of the HBTM and bee population interaction. In S. Arizona, it is clear that the best time to sample to determine HBTM infestation levels is from December through January since mite populations increase rapidly at that time and with fewer bees in the colony, it is easier to find bees with mites (we examine 30 bees per colony). The results are expressed as a percentage of that colonies' workers found to be infested with mites (%(w)).
Local beekeepers who have been requeening from their best surviving colonies have had very little problem with HBTM the last few years, but those who have recently taken colonies out-of-state (California, the Dakotas) have had colonies with severe HBTM infestations. A survey of mite populations in colonies of S. Arizona beekeepers conducted in Dec.-Jan. (1995-96) revealed that some (most) were mite-free, but colonies from the two migratory operations had mite levels (50-90%(w)) that were killing the colonies. The explanation for this is not clear, but at least 3 possibilities exist:
Genetic resistance to HBTM is available, especially in the Buckfast and the ARS-Y-C-1 (Yugo) bees (Danka et al., 1995) and in some locally selected lines although not enough is known as to the stability of this resistance (or the nature of it) under various climatic and management conditions.
Beekeeping in the current climate where HBTM, Varroa (and in the Southwest U.S., Africanized bees) are endemic is requiring more and better management and frequent sampling to determine infestation levels. Where genetic resistance is not yet available, judicious, timely applications of known, effective, and legal chemicals are required.