Sounds like powdered sugar could just be a myth,
Journal of Apicultural Research and Bee World 48(1): 72-76 (2009) © IBRA 2009
The efficacy of dusting honey bee colonies
with powdered sugar to reduce varroa mite populations.
Amanda M. Ellis1*, Gerry W. Hayes1, and James D. Ellis2
1 Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Bureau of Plant and Apiary
Inspection, Apiary Inspection Section, 1911 SW 34th St., Gainesville, FL 32614-7100, USA.
2 Honey Bee Research and Extension Laboratory, Department of Entomology and Nematology, University of Florida,
Bldg. 970 Natural Area Dr., Gainesville, FL 32611-0620, USA.
Received 5 August 2008, accepted subject to revision 15 October 2008, accepted for publication 16 December 2008.
*Corresponding author: Email: firstname.lastname@example.org
Controlling varroa mite (Varroa destructor Anderson and Trueman) populations in honey bee (Apis mellifera L.) colonies with acaricides has been a challenge for beekeepers due to the rapid development of resistant mite populations. For this reason, many beekeepers are adopting Integrated Pest Management strategies as alternatives to chemocentric varroa control schemes. One nonchemical tool that has been used for varroa control is dusting bee colonies with powdered sugar. The objective of our study was to determine the efficacy of powdered sugar as a varroa control by comparing mite populations, adult bee populations, and brood area in untreated colonies with those in colonies dusted every two weeks for 11 months with 120 g powdered sugar per application. We found that dusting colonies with powdered sugar did not significantly affect the adult bee population (treated: 10061.72 ± 629.42;control: 10691.00 ± 554.44) or amount of brood (treated: 4521.91 ± 342.84 cm2; control: 4472.55 ± 365.85 cm2). We also found no significant differences between the total number of mites per colony (treated: 2112.15 ± 224.62; control: 2197.80 ± 207.75), number
of mites per adult bee (treated: 0.080 ± 0.010; control: 0.097 ± 0.010), or number of mites per capped brood cell (treated: 0.112 ± 0.013; control: 0.106 ± 0.018). All data are mean ± s.e. Within the limits of our study and at the application rates used, we did not find that dusting colonies with powdered sugar afforded significant varroa control.
Discussion Despite the fact that powdered sugar dusting is innocuous to colonies of honey bees and would, therefore, be a good candidate as a varroa control agent, we found that our treatment protocol did not significantly reduce the total number of mites per colony, the number of mites per adult bee, or the number of mites per capped brood cell. We reject our hypothesis that biweekly dustings with powdered sugar would significantly reduce varroa populations. Even though dusting with powdered sugar resulted in significant mite fall initially (Fakhimzadeh, 2000), we did not find an overall reduction in colony mite populations within the limits of our study. This may be attributable to the reproduction rates of varroa mites under differing population pressures. Eguaras et al. (1994) observed that at lower mite densities, the reproductive rate of varroa increases. Therefore, the mite may be able to compensate for population loss due to dusting by increasing its reproductive rate. Even though different application methods were employed, Fakhimzadeh (2000) only measured mite fall 24 h after treatment, so it is unknown how effective the treatment would be in the long term, which
was addressed by our study.
Dusting only removes mites from adult bees and not mites reproducing in sealed brood cells. We found that, on average for each sampling month except November, approximately 60 % of the total mites per colony were located in the brood. For example, since 60 % of mites may be reproducing in brood at any given time, a control method that reduces even 90 % of the mites on adult bees will only result in a 36 % reduction of mites in the entire colony. To account for that in our study, we dusted colonies every two weeks for an entire year. This should have increased the efficacy of powdered sugar because we dusted colonies during times of the year when they were relatively broodless (winter). We still did not, however, find significant differences in mite populations between dusted and undusted colonies. Our results support the conclusion of Aliano and Ellis (2005b) that isolating broodless adult bees from their nest materials and dusting them in a separate box is the only way to effectively use powdered sugar to significantly reduce varroa infestations.
In summary, dusting colonies with powdered sugar did not significantly affect colony strength or mite populations. Within
the limits of our study and at the application rates used, we did not find this method of dusting colonies with powdered sugar to effectively control varroa mites.
Tom Dowda provided technical assistance with colony care, treatment administration, and data collection. Various members of FDACS Apiary Inspection, FDACS Bureau of Methods Development and Biological Control, and UF Honey Bee Research and Extension Laboratory assisted in data collection. Funding was provided by the Florida State Beekeepers Association and the Florida State Legislature as directed by the Florida Honey Bee Technical Council.