This past summer Colleen Granger, a University of Delaware Science and Engineering Scholar, and Maryann Li, a University of Delaware Honor Student, (with the support from Delaware Beekeeper donations) collected data about honey bee varroa mites and their effect on honey bees. Colleen will present the results at the upcoming March DSBA meeting.

One of the studies Colleen designed was a comparison of natural mite fall with mite fall of colonies receiving an Apistanâ strip. The mites were collected on sticky boards (manufactured by Olson Industries, donated courtesy of USDA Beltsville, MD) placed beneath window screen frames on the bottom boards of colonies at the University of Delaware Apiary. This study attempted to determine if use of Apistan was a more reliable indicator of mite population levels in a bee colony or if natural death rate could be used to reliably monitor mite levels.

The experiment was conducted from July 28 to August 1, 1998, and then repeated during the first two weeks of September. In the fall, there are higher numbers of mites found and natural mite fall has been used to estimate the population of mites in the colony. But the number of mites collected on the sticky boards is much higher when colonies receive an Apistan strip. One question Colleen wanted to answer was, since summer mite numbers are generally relatively low, would it be statistically better to monitor the colonies with Apistan in July, rather than simply using natural mite fall.

Results: Analysis of natural vs. Apistan-induced mite fall revealed that the two techniques gave very similar proportional mite numbers. Data shown in the two diagrams below reveal that average natural mite fall in both the July and September trials was between 18-19% of the Apistan-induced mite fall. The natural mite fall in the colonies tested in July ranged from 10-29% of the Apistan mite fall, and September natural mite fall ranged from 9-24% of the Apistan mite fall. As shown in the graphs, Colleen obtained relatively proportional results using either method. In July mite numbers were lower, especially on natural mite fall counts. This study suggests that even though natural mite fall results in lower numbers, the numbers are proportional to those found when placing an Apistan strip into bee hives. In conclusion, not only is natural mite fall chemically free and more economical than inserting Apistan strips, it is also a reliable way to test colonies for levels of varroa mites. These results will help us to further develop IPM mite control techniques.