ENVIRONMENTAL EFFECTS ON THE GROWTH OF VARROA MITE POPULATIONS

Authors: Harris, Jeffrey; Villa, Joseph; Danka, Robert

Submitted to: Bee Culture
Publication Type: Popular Publication
Publication Acceptance Date: 3/1/2004
Publication Date: 5/1/2004
Citation: Harris, J.W., Villa, J.D., Danka, R.G. 2004. Environmental effects on the growth of varroa mite populations. Bee Culture. 132(5):23-25.

Interpretive Summary: In this article, we summarized information about the growth of varroa mite populations over a 10-year period in Louisiana. Growth of varroa mite populations was greatly influenced by weather conditions. There were 3-4 years during the decade in which the growth rate for varroa mites was slow enough that damaging population levels were probably never reached during the spring-summer months (assuming that mite populations in the spring were low and only worker brood was available to the mites). Excessive cost and exposure of colonies to acaricides could have been avoided in those years if beekeepers had monitored the actual pest population and treated only when necessary.

Technical Abstract: We measured significant variation in the exponential growth rates for varroa mites (Varroa destructor) during 1993--2002 in Baton Rouge, LA. Mite population growth was monitored in colonies of honey bees with queens from miscellaneous U.S. sources that had not been selectively bred for varroa resistance. Mite populations were measured at the beginning and end of short field tests that started in the late spring of each year. Each estimate of mite populations included mites living on adult bees and mites living within capped brood cells. We used combs with only worker-sized brood cells, which simplified the estimates of growth rate by restricting mite reproduction to worker brood (varroa mites have higher reproductive rates in drone brood). The lowest growth rates occurred in three consecutive years of drought in Louisiana. Measures of ambient temperature and relative humidity correlated to growth of mite populations among different years. Reduced growth rates were probably the result of diminished reproductive rates or increased mortality for varroa mites during periods of hot and dry weather. The correlation of mite growth to weather suggests the need for monitoring mite populations in order to make decisions of when to use chemical treatments for the control of varroa. Chemical treatments may have been unnecessary during the drought years when the growth rates for varroa mites were low. Regimented use of chemicals during this period may have been a waste of money to beekeepers.