Small cells do not control Varroa mites
Whenever I write about small-cell combs and Varroa mite control I incur the wrath of the believers. It’s the one subject that delivers something very close to hate mail. So with that in mind, I will say it again: small-cell combs will not control your Varroa mites.
In a 2011 paper by Thomas D. Seeley and Sean R. Griffin—both of the Cornell University Department of Neurobiology and Behavior—small-cell combs were once again found to produce no fewer mites than regular-sized combs. This work, along with similar experiments reported by Ellis et al. 2009, Berry et al. 2010, and Coffey et al. 2010, demonstrates that small-cell combs given to European honey bees do not significantly reduce either mite loads or mite drops compared to hives with similar genetics and similar mite infestations.
In their experiment, Seeley and Griffin studied seven pairs of colonies. Each pair was started from a strong colony with a high mite drop. In order to assure that each pair had similar genetics and similar mite loads, the bees were shook from the parent colony and then divided into two packages. Each package was then given a new Minnesota Hygienic queen and fed sugar syrup. After three days, one package from each colony was put in a hive with standard-size combs (5.38 mm) and the other package was put in a hive with small-cell combs (4.82 mm).
Once a month for five months, the seven pairs of colonies were measured for colony strength, mite infestation, and worker size. The paper contains many interesting tidbits but, to make a long story short, by the end of the experiment Seeley and Griffin found no significant difference in either infestation rates (mites per 100 worker bees) or mite drops. They also found very little difference in worker size. Even though the small cells were 10.4% narrower than the average standard cells, the worker bees showed only a 2.1% decrease in head width and a 3.5% decrease in thorax width.
Taking this a step further, they divided the average thorax width of workers in standard cells (3.95 mm) by the cell width (5.38 mm) to get a “fill factor”– or the percentage of cell filled with bee (73%). Similarly, dividing the average thorax width of a small-cell bee (3.81 mm) by the small-cell width (4.82 mm) yielded a fill factor of 79%. This throws doubt on the commonly held belief that there is not enough room inside a small cell for mites to reproduce effectively. Neither 73% nor 79% are very tight fits, so there is plenty of room to grow many mites in either case.
I hear plenty of conflicting stories—anecdotal evidence of how changing to small cells cured the mite problem. But when researcher after researcher cannot reproduce those results, I have to wonder if the anecdotal cases aren’t due to exogenous variables or just plain luck. Sometimes we want something so badly we can’t think beyond the wishing. Believe me, if I thought there was a breath of truth to small-cell mite control, I would switch tomorrow.
 Seeley, Thomas D. and Griffin, Sean R. 2011. Small-cell comb does not control Varroa mites in colonies of honeybees of European origin. Apidologie 42:526-532, DOI: 10.1007/s13592-011-0054-4.
- Berry, J.A., Owens, W.B., Delaplane, K.S. (2010) Small-cell comb foundation does not impede Varroa mite population growth in honey bee colonies. Apidologie 41, 40–44.
- Coffey, M.F., Breen, J., Brown, M.J.F., McMullan, J.B. (2010) Brood-cell size has no influence on the population dynamics of Varroa destructor mites in the native western honey bee, Apis mellifera mellifera. Apidologie 41, 522–530.
- Ellis, A.M., Hayes, G.W., Ellis, J.D. (2009) The efficacy of small cell foundation as a Varroa mite (Varroa destructor) control. Exp. Appl. Acarol. 47, 311–316.
- Zhou, T., J. Yao, S.X. Huang, Z.Y. Huang. 2001. Larger cell size reduces varroa mite reproduction. Proceedings of the American Bee Research Conference, American Bee Journal 141: 895-896.
- Taylor, M.A., Goodwin, R.M., McBrydie, H.M., Cox, H.M. (2008) The effect of honeybee worker brood cell size on Varroa destructor infestation and reproduction. J. Apic. Res. 47, 239–242.