Submitted to: American Bee Journal
Publication Type: Abstract Only
Publication Acceptance Date: January 9, 2006
Publication Date: May 11, 2006
Citation: Villa, J.D. 2006. The effects of seasonal fluctuations in population densities of varroa mites on the survival of untreated colonies. American Bee Journal 146(5):450 Technical Abstract: Rapid increases of varroa mites in colonies, summer mortality of untreated colonies, and the disappearance of feral colonies were common after the detection of mites in 1992 in this area. Recently, local observations and reports from various areas of the United States, suggest that some of these negative effects may have moderated. I monitored the density of varroa mites in untreated colonies for six years (2000-2005) to observe seasonal trends in infestation, to relate infestation to colony mortality, and to use this information to develop economic thresholds. Samples of adult workers (ca. 150 g) were taken four times per year from colonies not receiving miticide treatment. Fifty colonies produced a total of 277 samples (1-21 samples per colony). A total of 38 colony deaths were observed, and as colonies died they were replaced to maintain about 15 colonies available for sampling at a given time. Half of the colony deaths occurred after the sampling period of Nov-Jan. For that period, the infestation of colonies that died was significantly higher than that of surviving colonies. Another significant period of mortality occurred after Aug-Oct, but for those samples, subsequently dead vs. live colonies did not differ significantly in infestation. Pooling the data from all seasons, only 9% of colonies with infestations below 0.25 mites per g of adults died, while 73% of those above 1.5 mites per gram died. Based on these data, and on observations of symptoms of infestation, 0.5 mites per gram of adult bees may be a useful economic threshold for southern Louisiana.