In the November 1998 issue of The American Bee Journal (pp. 828-832) we reported the results for the first two years of our effort to develop a Varroa-tolerant population of honey bees (Erickson et. al., 1998). We demonstrated that it is relatively easy to find Varroa-tolerant colonies among those in managed apiaries, and to propagate and maintain Varroa-tolerant honey bees in the absence of other mite control measures. Also reported were corroborating data obtained from collateral studies which clearly showed that some beekeepers/bee breeders are currently doing this. In this brief article we provide an update on the continuing research. Our methods remain unchanged from those first reported except that we now sample the colonies less frequently.

0ur 65 colony Varroa-tolerant study population is composed of colonies of both European and African descent and their hybrids (virtually all of Arizona is colonized by Africanized honey bees). Even so, Mr. Hines continues to eliminate from the breeding program any queen whose progeny tend to be overly defensive, without regard for their ancestry. Also, we should note here that we have not seen evidence to suggest the Africanized honey bees are consistently more Varroa-tolerant than European stock. Moreover, our earliest sources of Varroa-tolerant stock were identified prior to the arrival of Africanized honey bees in Arizona and, thus, were European.
 

We have now maintained this Varroa-tolerant honey bee population since November, 1994 via selective breeding, queen mating in isolation, and conventional beekeeping practices, without the use of any other mite control strategies. All colonies were last examined and sampled on July, 27, 1999. Three colonies were queenless, and three others had evidence of a break in brood rearing and new supersedure queens. Two colonies, although vigorous, had visible evidence of Varroa infestation. All remaining colonies appeared Varroa free. They were populous and vigorous with expansive solid brood patterns, and were producing surplus honey. Earlier in the year one of the colonies had exhibited signs of Varroa damage and had been requeened July, 8, with a program queen: When inspected, this colony had no evidence of Varroa.

The study colonies are rather evenly divided among three apiaries isolated from other managed colonies, but not from feral colonies. All of the parent stock came from managed apiaries in Central and Southern Arizona. Colonies (or queens therefrom) surviving in untreated apiaries, or with noteworthy low Varroa infestation levels provided our initial stock. We have since requeened nearly all of Mr. Hines' 700 colony commercial operation with 'program queens', hence, these colonies now provide an additional source of queen mother colonies. Our Varroa-tolerant population has survived for nearly five years with mean annual infestation level (number of mites per 100 bees) between 6 and 7 percent (Figure 1). Samples of the mites were taken and sent out for further identification. All samples were identified as being of the 'Russian' genotype (de Guzman et. al., 1999) which some have suggested may be more virulent than the 'Japanese' type. Tracheal mite infestation levels are also monitored and remain low (Figure 2).

Infestation levels in our Varroa-tolerant stock remained low both during times of stress and abundant resources. Abnormally low precipitation during 1996-97 led to a significant reduction in the availability of floral resources. Little surplus honey or pollen was harvested and some colonies had to be fed to ensure their survival. Thus, the colonies experienced a significant level of stress throughout this period. Even so, it was interesting to note that from time to time Varroa could not be detected in some colonies. 1998 was an El Nifio year and as a result, floral resources were abundant. Varroa infestations remained low and honey production among the three Varroa-tolerant apiaries was uniform and averaged 90 pounds per colony.
 

With the requeening of nearly all of Mr. Hines' colonies with program queens comes the opportunity to observe more extensively the performance and impact ofthese queens. Up through 1997 and prior to this almost complete requeening, Mr. Hines noted that "he would begin seeing serious effects of varroa ( e.g. high mite counts, diseased brood syndrome(s), and colony population dwindling) by late July. In 1998 these symptoms were seldom seen until late September or early October and then less frequently than before." He reports seeing very little to zero indication of Varroa damage in most of his colonies through July 1999. Extensive sampling of his entire operation will be undertaken this fall to determine the overall level of infestation.

We are now expanding our study to determine, where possible, those factors which contribute to the Varroa-tolerance in our population. Initially, we will determine the extent to which program colonies (1) exhibit hygienic behavior, and (2) whether adult bee emergence time has been reduced by our selection and breeding. These results should be available later this fall.

The Carl Hayden Bee Research Center is now engaged in research to develop an Integrated Pest Management (IPM) program for Varroa based on the strategies that have led to the development of our Varroa-tolerant stock. Our goals are to eliminate the use of pesticides and hold Varroa infestations below 5%. One cornerstone of this program has been completed - that of demonstrating that Varroa-tolerant bee populations can be developed out of existing domestic stock. Second, a study to evaluate the merits of using brood combs with smaller cell diameters as a colony

management strategy to further reduce Varroa infestations is in its second year of study and, preliminary indications are encouraging. A third cornerstone of the IPM program is the use of natural products with miticidal activity. Five highly effective natural products have been identified and evaluated, and the development of delivery systems is underway. Conceivably, these products would either be used intermittently as needed, or to facilitate transitions from current pesticide-based mite control programs to Varroa-tolerant populations. The framework for the IPM program has been completed. "Area-wide" implementation of this program is anticipated for the year 2000 and beyond.
 

Acknowledgments

The authors especially wish to thank Mr. Joe Martin who reared the numerous us queens used throughout this study. We also thank Mr. Gilbert Mills for his assistance in helping maintain and conduct this study, and Dr. Dennis Anderson for identifying the mites.

References

de Guzman, L. I., T. E. Rinderer, and J. A. Stelzer.

1999. Occurrence of two genotypes of Varroa jacobsoni Oud.

In North America. Apidologie 30:31-36.

1998. Can we produce Varroa-tolerant honey bees in the United States?

Amer. Bee Jour. 138:828-832.