Not many people know that there are actually two domesticated honey bee species: Apis cerana (the Asian honey bee) and A. mellifera (the European honey bee). A. mellifera is the better honey producer of the two and absconds less often, so early settlers quickly spread them across the continents, whereas A. cerana has remained in Asia (but it’s still a big contributor to the Chinese honey supply). A. mellifera may be the most widely kept bee in the world, but A. cerana out-performs A. mellifera in one very important area: combatting Varroa. A recent article titled “Go East for a Better Bee: Apis cerana is faster at Hygienic Behaviour than A. mellifera” highlights these key desirable traits.
A. cerana has co-evolved with Varroa for millions of years, whereas A. mellifera has not had that luxury. This means there are several traits found in A. cerana that help it tolerate Varroa infestation, rather than be destroyed by it. Perhaps counter-intuitively, this is actually favourable (from an evolutionary perspective) for Varroa as well; a successful parasite usually does not kill its host – at least not quickly – because it ultimately depends on the host for survival.
First, A. cerana has a smaller body size and shorter developmental time. These features work together to limit the number of progeny coming from a single mite family, since it reduces available nutrients from the developing pupa, as well as time for the juvenile mites to reach maturation. Conversely, the reason mites preferentially infest drone cells is thought to be because of the larger body size and longer developmental time. In an A. mellifera drone cell, an average foundress mite can yield 4 to 5 mature daughters, whereas an A. mellifera worker cell will yield only 1 to 2. In fact, mites do not usually even infest A. cerana worker cells and almost exclusively prefer the drone brood, where they are often entombed, never to emerge at all.
Second, and maybe most interestingly considering the BeeOmics project, A. cerana is actually more efficient at performing hygienic behavior than A. mellifera. This means A. cerana has not only developmental and morphological adaptations to combat mites, but also behavioural adaptations. This was the focus of the research article (Go East for a Better Bee: Apis cerana is faster at Hygienic Behaviour than A. mellifera, by Z. Lin et al. (2016)). The article was published in PLOS One, an open access journal, so it is freely available for all of you to read. It is somewhat gratifying to see that the precise trait we are working to enrich in A. mellifera is also what millions of years of evolution has favoured in A. cerana.
This article appeared in the Winter 2016 issue of Bee Scene.