Too young for field work
By now you’ve probably heard about the newly published study, “Rapid behavioral maturation accelerates failure of stressed honey bee colonies¹.” In my opinion, this is the first paper suggesting a possible cause of colony collapse disorder (CCD) that actually makes sense.
The scientists doing the research used transmitters to learn about the behavior of bee colonies that were under stress. They found that when the foraging force of older workers is rapidly reduced for any reason, young bees quickly replace the missing foragers.
Now this, by itself, isn’t news. Beekeepers have long been aware that worker bees do what is necessary to maintain the colony, and workers will change “jobs” to meet the demand.
But here’s the surprise: they found that young workers who prematurely became foragers made fewer total foraging trips than the older workforce and were more likely to die on their first trip out.
According to the article, in a healthy hive, a worker becomes a forager at 2 to 3 weeks old. But when a colony experiences a situation where more foragers are needed in a hurry, bees that are much younger begin to do the foraging. However, according to the study, these bees are not quite ready for this task and often perish early on. Imagine giving your eight-year-old the car keys and telling him to go buy bread and milk.
So how does this relate to CCD? Well, picture this: you have an active, healthy colony. But for some reason, the foraging force gets in trouble. It could be a pesticide kill, it could be a disease like Nosema, it could be stress from poor nutrition, it could be stress from lack of flowers, or a combination of factors. As a result of the stressors, a large portion of the foraging force dies.
When a large part of the foraging force goes missing, a percentage of the nurses become foragers to take up the slack. But many of these underage or “precocious” foragers don’t make it and they die in the field. As a result, even more of the nurses must become foragers, and many of these die, too.
It doesn’t take long for the colony to go out of balance: there still aren’t enough foragers but now a large part of the nurses are gone as well. Not enough nurses remain to raise a lot of bees, so the brood nest becomes very small and produces very few replacements.
The young foragers die in the field without returning to the hive, and the brood nest is small with just a few bees and a queen remaining. Sound familiar?
The theory isn’t perfect. For example, it doesn’t explain why predators are slow to move into a CCD colony. But overall, it makes sense. It explains why the bees seem to vanish. It explains why the queen is still alive while most bees have disappeared. It explains why the brood nest is so small. It also explains why some collapsed colonies have Nosema and some don’t, why some have many viruses and some don’t, and why some are in heavily infested with mites and some are not.
Like any study, it needs to be replicated and examined. In time perhaps more answers will emerge, but I feel like we are very close to understanding CCD. Now we just have to decide what to do about it.
¹Clint J. Perry, Eirik Søvik, Mary R. Myerscough, Andrew B. Barron. Rapid behavioral maturation accelerates failure of stressed honey bee colonies. Proceedings of the National Academy of Sciences, 2015; 201422089 DOI: 10.1073/pnas.1422089112