Queen bees use chemical signals to keep their daughters home

By Stephen Beech

Queen bee pheromones help their daughters decide whether to stay or leave the nest, reveals new research.

Chemical signals help determine whether offspring remain and work for the queen or leave to establish nests of their own, say scientists.

They explained that female sweat bees need to make a "pivotal" life decision — remain in the nest to help their mother raise more offspring or leave to establish nests of their own.

Researchers at the Smithsonian Tropical Research Institute (STRI) in Panama found that queen pheromones help influence that choice, offering new insight into how cooperation evolved in insect societies.

The study, published in the journal Proceedings of the Royal Society B, identified for the first time that, via pheromones, sweat bee queens communicate to their daughters that sticking by them is a worthwhile investment.

STRI postdoctoral fellow Callum Kingwell explained that when sweat bee daughters grow up, their lives head in one of several directions.

Some remain in the nest as nonreproductive helpers — or "worker bees" — while others leave their mother's nest and establish their own, either as a solitary queen or as the founder of a new social nest.

The research team speculated that their decision depends on the queen's health and whether leaving the nest affords the colony the best chance of passing on her genes.

The team wanted to know whether chemical signals from the queen contributed to their daughters' choices.

Kingwell said: "We are interested in the evolution of cooperation, and in this case, how sweat bees decide whether cooperation is worthwhile.

"Our observations provide a rare window into how insect societies may first evolve."

The researchers studied cooperation between queens and their daughters on Barro Colorado Island in the Panama Canal by placing hundreds of artificial nests in the bees' natural habitat over several years.

The team marked individual bees and recorded videos of their behavior to determine whether daughters stayed and worked, usurped the queen or left the nest to reproduce elsewhere.

To assess whether chemical signals contributed to the choice, the researchers characterized the chemicals coating the bees' bodies using advanced analytical techniques, including gas chromatography coupled with mass spectrometry — two techniques that help identify and quantify individual chemical compounds.

Kingwell said: "A particularly novel aspect of this study was performing chemical analyses directly on Barro Colorado Island and repeatedly sampling live bees, allowing us to track chemical signaling in the same free-living individual bees throughout their lives."

The research team found that queen pheromones influence daughters in two ways.

During a critical stage of development, pheromone levels rose in the queen and inhibited their daughters' ovarian development.

The same chemical signals also appeared to indicate the queen's reproductive health.

When pheromone levels were higher, daughters were more likely to remain and help.

Together, the research team says their findings suggest queen pheromones help daughters choose between helping their mother produce more offspring or reproducing independently.

Study co-author Bill Wcislo said: "Chemical signals like these may stabilize nascent insect societies, buying time for social complexity to emerge over evolutionary time.

"This represents, to our knowledge, the first queen pheromone identified for a flexible social insect."

Kingwell added: "The evolution of cooperation is a fundamental question that extends far beyond insects.

"Our work shows how chemical communication can help individuals decide when cooperation is worthwhile, offering insights relevant to evolutionary biology, animal behavior and social systems generally."