Monday morning myth: small-cell foundation discourages Varroa mites
The idea that small-cell foundation may limit the reproduction of Varroa mites resurfaces frequently. However, carefully controlled research has shown that mites may actually increase on small cell foundation. A carefully researched paper on the subject by Berry, Owens, and Delaplane was recently published in the journal Apidologie and can be downloaded here.
In the states, small-cell foundation has cells that are 4.9 mm wide and standard foundation has cells that are 5.3 mm wide. But what we now call “small cell” was actually the natural cell size back in the early 1900s. At that time bee breeders thought that they could improve on honey bees by growing bigger bees that would produce more honey.
They created these beasts by manufacturing foundation with larger cells. Sure enough, in not too many generations, the bee larvae filled the cells and the resulting adult bees were bigger. We are still using these “big bees” today.
Then in 1995 some scientists noticed that Africanized bees—which are slightly smaller than European bees—had lower mite counts. So the idea was born that the natural (smaller) cell size might impede the growth of Varroa mites. This idea was supported by earlier research that showed that when immature male mites are squeezed between the bee pupae and the cell walls, they often die.
With this in mind, beekeepers started regressing their colonies. That is, they tried to do the opposite of what the beekeepers in the early 1900s did: they provided smaller foundation in the hope that male mites would get squeezed to death in the tight confines of the smaller cells.
But, just as bees on large foundation grow bigger, bees on small foundation become smaller. So, in not too many generations, the male mites were no longer squished against the cell walls—and everything was just fine and dandy in mitedom.
This is not to say regressing to small cells is a bad thing. In fact, other research shows that natural sized bees may be more efficient pollinators and more healthy in general. But don’t count on small cells to take care of your mite problem . . . it just won’t happen.