A Survey of Tracheal Mite Resistance Levels in U.S. Commercial Queen Breeder Colonies
Research has shown that honey bee strains having genetic resistance to tracheal mites (Acarapis woodi) can be used to help to solve the problems resulting from parasitism by this mite. Colonies of resistant bees tend to withstand challenge from tracheal mites and remain productive without treatment, while susceptible colonies tend to become infested at damaging levels.
Resistance to tracheal mites is of interest to bee breeders who are trying to improve stock quality. Identifying the level of resistance in breeding colonies should be a critical part of such breeding efforts. However, little is currently known about the resistance in the commercial breeding population used to supply queens for the U.S. beekeeping industry. Our objectives were to measure the range of resistance in a sample of U.S. commercial breeder colonies, and enable participating queen breeders to improve the quality of their stock by providing selection guidance.
Eight commercial queen producers from five states submitted brood from 6 to 19 breeder colonies each so that emerging bees could be evaluated for relative resistance to tracheal mites. Young, uninfested bees from each colony of an individual queen producer, and also from colonies of two reference stocks (one known to be resistant to tracheal mites and one known to be susceptible), were marked and then simultaneously exposed to mites in infested colonies. They were retrieved after 4-6 days and dissected to determine resulting mite infestations. Results for the breeder colonies were adjusted to the average results of the resistant and susceptible reference colonies with which they were tested.
The 83 breeder colonies varied widely in their responses to tracheal mites. About two-thirds were statistically similar to the resistant reference and one-fourth were similar to the susceptible reference. Three queen producers had 30 of 31 breeder colonies that were classified as resistant. The other five queen producers had breeder colonies that were very variable and of which 40% were susceptible.
Levels of resistance to tracheal mites found in breeder colonies used by eight U.S. commercial queen producers. For each colony, the resistance index (RI) shows the colony resistance relative to that of a resistant reference stock (resistance index set at 0.0) and a susceptible reference stock (resistance index set at 1.0). The number of colonies of each operation that was tested appears immediately above the horizontal axis.
The most striking result of this survey was the variability in levels of tracheal mite resistance among colonies of U.S. commercial breeding stock. This breeding population can be expected to yield propagated queens that range widely in quality: some queens will be useful in improving stock by imparting resistance, while others will predispose their colonies to damaging mite infestations. In the absence of knowledge about the resistance levels of individual breeder colonies, the performance (vis-vis tracheal mites) of production colonies headed by commercial queens becomes largely a matter of the chance associated with a queen producer=s random selection of a grafting source from among his or her breeder colonies.
Fortunately, the majority of colonies we tested had useful resistance to tracheal mites. However, queens propagated from susceptible colonies and then widely distributed through commercial sales may contribute to the lingering problems associated with tracheal mites across the country. The findings from this survey emphasize the value of testing in enabling effective selection for resistance to tracheal mites. Through testing, susceptible colonies are easily identified and can be eliminated. Several of the queen breeders who participated in this survey reported that susceptible colonies were removed from their breeding programs soon after they received the test results.
Reference to full article:
DANKA, R. G. and J. D. VILLA. 2000. A survey of tracheal mite resistance levels in U.S. commercial queen breeder colonies
. American Bee Journal 140: 405-407.