Bee vs. Mite! – Puerto Rico’s Honey Bees take on the Varroa Mite

Part 2: Bee vs. Mite

See here for an introduction to colony collapse disorder and part 1 of this two-part series.

Africanized bees, more often known as "killer bees," have earned notoriety as opportunistic attackers of, well, just about anything that gets in their way. While Africanized bees are in general substantially more aggressive than their European counterparts, they also exhibit beneficial traits like efficient honey production and disease and pest resistance.

Last year, a collaboration between investigators at the Inter American University of Puerto Rico, the University of Puerto Rico, and Namik Kemal University identified a novel grooming behavior in Africanized bees in Puerto Rico. This behavior might be an effective tool against colony collapse disorder (CCD). Fortunately, unlike their relatives, the Africanized bees that have colonized Puerto Rico show only mild aggressiveness.

The New World has seen two waves of honey bee invasions. In the first wave, when the powers of 17th century Europe were establishing colonies in the Americas, the colonists set up colonies of their own: colonies of honey bees. The second wave began centuries later, in 1956, when Africanized bees were brought to Brazil to boost the area honey trade. After their initial release, the bees crept steadily northward to their present range, which extends to portions of the southern United States, particularly the southwest. The bees don't seem to be capable of weathering the cold winters farther north.

For one reason or another, perhaps because of the ecology of their island habitat, Africanized honey bees in Puerto Rico show markedly reduced aggression. However, they have maintained the pest and disease resistance already known to exist in the Africanized bee population.

One of the most pressing honey bee pests today is the varroa mite, which latches onto bee larvae and adults and feeds on their hemolymph. In addition to weakening honey bee hives, the mites can act as vectors for other bee pathogens. In the southern United States, where I keep bees, varroa mites are found in every single hive. Puerto Rico is likewise infested with this parasite.

In laboratory experiments, the authors of this paper found that Puerto Rico's Africanized honey bees are much more likely to remove attached varroa mites by grooming compared to their European cousins (a full 100% versus slightly less than half). Additionally, after beginning to groom, the Africanized bees did so with more determination, spending on average 1 minute grooming compared to 10 seconds for the European bees. This paid off, as about a third of the Africanized bees in the tests successfully dislodged the mite, while none of the European honey bees were successful. Perhaps the most dramatic observation was that some of the Africanized bees, after removing the mite, proceeded to bite it in two!

These defensive measures against varroa mites are likely the reason why the Africanized bees of Puerto Rico (and, we could infer, elsewhere) have lower mite loads. Perhaps the reduced presence of varroa mites also accounts for the lower general abundance of disease that is associated with Africanized honey bees. If so, Puerto Rico's Africanized honey bees are the best of both worlds, with the docility of the European honey bee and the pest and disease resistance of the Africanized honey bee.

Direct introduction of the bees to the United States or Europe probably wouldn't work, since Africanized bees fare poorly where the winters are cold. However, identifying the genetic basis of anti-mite defensive behaviors could help guide breeding programs for pest and disease resistance. Of course the mites won't appreciate this very much, but what can they do? Aside from selection for a stronger grip to the bee, thereby decreasing grooming success, there is little they can do. Devastatingly for the mite, the authors of the paper note that the bees attack mites even with no preceding grooming behavior, and no provocation on the part of the mite is necessary.

Giving bees maximum self-sufficiency is a popular notion among beekeepers and something that I myself espouse. We all know that, between direct negative effects on bees and rapid evolution of resistance, chemical treatments for mites aren't going to work for bees in the long run. Hopefully this new finding will let us help the honey bees we rely on take care of themselves better than they can currently.

Check out these videos of Puerto Rico's Africanized honey bees self-grooming and attacking mites, courtesy of the authors of this study.

References:

1. Rivera-Marchand, B., Oskay, D., & Giray, T. Gentle Africanized bees on an oceanic island. Evolutionary Applications 5, 746-756 (2012).

2. Schneider, S. S., DeGrandi-Hoffman, G., & Smith, D. R. The Africanized honey bee: Factors contributing to a successful biological invasion. Annual Review of Entomology 49, 351-376 (2004).

3. USDA Agricultural Research Service. Spread of Africanized honey bees by year, by county.