J. P. Parkman, J. A. Skinner and M. D. Studer

Department of Entomology & Plant Pathology

University of Tennessee - Knoxville

The Varroa mite, Varroa destructor, is the most damaging pest to honey bees in North America and most of the world. Populations of Varroa destructor have exhibited resistance to the only chemical miticides registered for use in the US. A second year of a tri-state (TN, SC and GA) evaluation of combined non-chemical management tactics for Varroa was completed in 2003. Management tactics included honey bee stock expressing mite resistance; screened, open bottom boards; and isolation of apiaries.

Bee colonies in two groups of apiaries (isolated and non-isolated) were subjected to one of four treatment combinations: (1) resistant honey bee line + open bottom board (OBB), (2) resistant honey bee line + conventional (solid-floor) bottom board, (3) non-resistant honey bee line + open bottom board and (4) non-resistant honey bee line + conventional bottom board. Test colonies, consisting of brood and workers taken from mature, overwintered colonies, were established in April in South Carolina and May in Tennessee. Colonies were requeened with new queens purchased from commercial queen producers.

In Tennessee and South Carolina, results for 2003 were not as promising as those for 2002. Varroa populations rose steadily in almost all colonies and there was no difference in mite populations among the treatment combinations. Possible reasons for lack of mite reduction include (1) initial mite load at beginning of study was greater (in 2003 we began the study using mature, overwintered colonies, some containing many Varroa; in 2002 we began with small package colonies with few Varroa) and (2) using open-mated queens where the paternity of workers was unknown, possibly diluting the resistant trait. Selected colonies were tested for being hygienic or expressing the suppression of mite reproduction (SMR) trait. There was no difference in resistance between resistant and susceptible colonies.

In 2002, queens instrumentally inseminated with resistant drone sperm were used. Therefore, workers were 100% resistant. Open-mated queens (used in 2003) were purchased from commercial queen breeders. Their failure to maintain Varroa below damaging levels indicates breeders need to improve mating techniques to insure queens are mating with resistant drones (or, at least, a majority of resistant drones.)

In Georgia, treatment effects were measured beginning in spring 2002: 21 tri-weekly samplings were made over 81 weeks (rather than conducting a separate experiment in each year). As of October 2003, economic threshold was significantly prolonged in isolated apiaries and in colonies headed by SMR queens. Mite levels were reduced in colonies with SMR queens in 14 of 21 sampling weeks, six differences of which were statistically significant. Overall mite levels (mean for 21 dates) were significantly lower in SMR colonies (7.7 mites per d) than in those containing non-resistant queens (9.3 mites). Mite levels were reduced in colonies with OBBs in 11 of 21 sampling weeks, one of which was statistically different. Overall mite levels were significantly lower in colonies with OBBs (6.5 mites per d) than in solid bottoms (10.2 mites). Queens used were either instrumentally inseminated or daughters of instrumentally inseminated queens.

Although 2003 results for Tennessee and South Carolina were disappointing, we believe quality of commercially available resistant queens will improve and the use of a combination of non-chemical tactics is a viable management option for Varroa.

A project was initiated in the fall of 2002 to provide Varroa management tools to selected beekeepers across Tennessee. Participants are members of the Tennessee Beekeepers Association (TBA) and maintained bees in 10 counties located across the state: west (Shelby), central (Bedford, Montgomery, Moore, Robertson, Williamson) and east (Knox, Loudon, Sevier, Union). In spring 2003, beekeepers were provided resistant and susceptible (for comparison) queens and OBBs, and sticky board traps to sample for Varroa. University personnel visited each site to assist with requeening bee colonies and to install OBBs. Correct use of mite traps was demonstrated. Participants routinely collected mites to determine efficacy of resistant stock and OBBs.

Queens used in the demonstration were purchased from the same suppliers used in the research study; therefore, resistance was not expressed and Varroa populations increased in most colonies. Despite this setback, use of non-chemical management tactics appears to be increasing in Tennessee. Based on results of a questionnaire distributed to TBA members, 55% of beekeepers responding began using, or increased use of, IPM tactics (mite-resistant stock and/or open bottom boards) in 2003.

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Copyright © 1999 by The University of Tennessee. All rights reserved.

This research represents one season's data and does not constitute recommendations.  After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.