Bee size, mites, and pesticides
Many beekeepers are convinced that raising smaller, natural-sized bees is the answer to controlling Varroa mites. According to one theory, smaller bees mature faster—in about 19 days instead of 21. This shorter cycle means there is less time for the offspring of a Varroa mite to mature and mate before the adult honey bee emerges from the capped cell. Since a female mite lays one egg every 30 hours, that would mean mites in small cells produce approximately one less mite per brood cycle.
Let’s assume small cell works
That is still a lot of mites. However, today I want to assume that small bees are so successful at controlling Varroa mites that they can be successfully-raised treatment free. If that is true, why are some beekeepers so much more successful at it than others?
I had been pondering this while reading Pollinator Protection: A Bee & Pesticide Handbook (Johansen & Mayer). The text explains that most bee poisoning results from the chance adherence of insecticide residues onto the bee’s body. Then the authors state, “Body size appears to have a direct effect on the susceptibility of bees to insecticides. As a general rule, larger bees are more tolerant of insecticides than are smaller bees. Smaller bees have a higher surface-to-volume ratio and are more susceptible.”
Surface area-to-volume ratio
The surface area-to-volume ratio of similar-shaped objects changes with the overall size. Given a constant shape, the surface area-to-volume ratio will decrease as the shape gets bigger, and increase as the shape gets smaller. That means that a smaller bee has a lot more surface area to pick up a poison compared to its overall body size.
In this case, the authors compared leafcutting bees, alkali bees, honey bees, and bumble bees and they actually measured the surface area-to-volume ratios. Sure enough, leafcutting bees are more susceptible than alkali bees which are more susceptible than honey bees which are more susceptible than bumble bees in a field of treated blooms. As the authors say, “Smaller insects require less chemical to kill them.”
Are small honey bees more susceptible?
This study did not compare small honey bees with large ones, but it begs the question: Are small honey bees more susceptible to insecticides than larger ones? If so, then perhaps small cell bees living in areas with few pesticides do better than small cell bees in areas with lots of pesticides. Maybe it answers the question of why some beekeepers are more successful with small cell than others. Factors other than Varroa mites need to be considered.
I am not drawing any conclusions herenot a single oneI’m only posing some questions. But you can’t take one factor, for example small cell size, and say it is better or worse for bees without examining all possible ramifications. Surely you can argue that bees evolved over millions of years with a smaller cell size, but you could also argue that bees did not evolve along with commercial pesticides. So maybe the larger size helps?
So with no other agenda, I simply pass this query on to you, so that in the wee hours of a cold winter’s night, you have something to ponder.