November/December 2004
Keeping the Little Ones Down
A recent discovery unveils the chemical secret that gives old bees the authority to keep young
bees home babysitting instead of going out on the town. A hard-to-detect pheromone explains a phenomenon Michigan State University researchers observed twelve years ago - that somehow older forager bees exert influence over the younger nurse bees in a hive, keeping them grounded until they are more mature, and thus more ready to handle the demands of buzzing about. The work that identifies the chemical, “Regulation of Behavioral Maturation in Honey Bees by a New Primer Pheromone” was published in Proceedings of the National Academy of Science Biological Sciences, Population Biology, Early Edition. “If the older ones don’t keep them in check, the young ones can mature too quickly,” said researcher Zachary Huang. “It’’s kind of the same thing as with people, you need the elders to check on the young, even if the young are physically able to go out on their own, it’s not the best situation for anybody and now we know how it works.”
Huang worked with a team that spanned from the United States, France and Canada to explain how the bees kept an exquisitely consistent balance between the ones that go out to collect nectar and pollen and defend the hive, and those that stay home and nurture the larvae. Huang had documented that this balance is controlled by the elder bees, those that typically spend the final one to three weeks of their five-week lifespan out in the field. Experiments showed that if a significant number of forager bees didn’t come home, the young nurse bees would mature ahead of schedule and head out to become foragers themselves. If the older bees were kept inside more than usual - as in an extended rain shower - fewer young bees would mature, and instead stick to brood care. But the question was always, why?
Pheromones are a chemical signal emitted by animals, insects and humans. Some, called releaser pheromones, are like a quick conversation that changes behavior, such as those that inspire sexual attraction. Since releasers change behaviors immediately, they historically have been easier to identify. Hundreds of releaser pheromones have been chemically identified, whereas only four (including this new one) have been identified as primer pheromones. Primer pheromones are more difficult to work with because they impart behavioral changes on a much longer time scale, taking days or sometimes weeks to see an effect. Huang and his associates spent years futilely searching for a primer pheromone. After many dead ends, the group came upon a crucial difference between forager bees and nurse bees: forager bees carry a large amount of a chemical called ethyl oleate in the abdominal reservoir in which they store nectar. That, Huang said, led them to identify ethyl oleate as the primer pheromone.
Forager bees load up on ethyl oleate when they’re buzzing about gathering food, but don’t digest it. The forager bees feed the chemical to the worker bees, and the ethyl oleate keeps them in a teenage state, sort of like being grounded to watch the younger siblings. As the old bees die off, the chemical no longer is fed to nurse bees. Eliminate ethyl oleate and the bees mature into foragers. Huang said the system makes sense for the health of the hive. Young bees - those in the first two to three weeks of life - are biologically better suited for brood care, thanks to some boosted blood protein. Bees forced out too early aren’t great navigators, and since foraging is dangerous, they risk dying before their time. “Our idea has never been disproved, but the lack of mechanism drove me crazy,” said Huang. “Now we know the specific chemical that controls the behavior of honey bees for the good of the whole population.” (Michigan State University Newswise, 11/29/04).
