Some beekeepers report success using approximately 4.8–4.9 mm worker cells as part of a treatment-free approach to Varroa destructor. The proposed explanations include reduced mite invasion or reproduction and changes to the brood-cell environment. Those observations are worth examining, but controlled studies have not established 4.9 mm foundation alone as a reliable Varroa-control method in European-origin honey bee colonies.
What controlled studies found
Ellis, Hayes & Ellis (2009) found no significant benefit from small-cell foundation for total mites, mites per brood cell, or mites per adult bee under their Florida study conditions. Seeley & Griffin (2011) compared paired colonies on 4.8 mm and 5.4 mm comb and likewise found no difference in mean mite loads.
An important exception
Piccirillo & De Jong (2003) found a different pattern in Africanized honey bee colonies. Naturally built 4.84 mm cells had 10.3% brood-cell infestation, compared with 13.9% in 5.16 mm cells and 19.3% in 5.27 mm cells. This demonstrates that cell size can influence bee–mite biology in some circumstances, but it does not establish that 4.9 mm foundation will reliably control Varroa in European-origin colonies.
The 2024 twist
Zhang and colleagues (2024) tested Varroa reproduction under laboratory conditions using 3D-printed worker-cell foundations ranging from 5.0 to 7.0 mm. Surprisingly, mite fecundity and fertility decreased as cell size increased. The researchers proposed that larger spaces may disperse or weaken host volatile chemical cues involved in triggering mite reproduction. This was laboratory evidence, not a recommendation to use oversized worker cells in production colonies.
Bottom line
Cell size clearly can affect aspects of the honey bee–Varroa relationship, and treatment-free beekeeper experiences are useful observations deserving investigation. But individual experiences cannot by themselves establish cell size as the cause. Based on controlled field evidence to date, small-cell foundation should not be assumed to provide reliable Varroa control by itself. Beekeepers should measure colony mite levels and base management decisions on actual colony conditions.
Research cited
- Ellis, A.M., Hayes, G.W. & Ellis, J.D. (2009). The efficacy of small cell foundation as a varroa mite control. Experimental and Applied Acarology 47:311–316.
- Seeley, T.D. & Griffin, S.R. (2011). Small-cell comb does not control Varroa mites in colonies of honeybees of European origin. Apidologie 42:526–532.
- Piccirillo, G.A. & De Jong, D. (2003). The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies. Genetics and Molecular Research 2(1):36–42.
- Zhang et al. (2024). Large cells suppress the reproduction of Varroa destructor. Pest Management Science. DOI: 10.1002/ps.8249.