Colony density triggers bee puberty, not hormones

Bees sense the density of workers in the colony. Once a specific size and density threshold is surpassed, workers begin making more drone comb. Photo by Michael Smith/Cornell

May¬†6 (UPI) — New research suggests bees can sense when the colony has grown large enough to begin investing resources in reproduction instead of only survival.

At a certain point, workers begin making a kind of beeswax comb called drone comb. The drone comb nourishes the new drones — reproductive males.

But how do bees know when to alter their behavior? What triggers the colony’s sexual maturity, or puberty?

Research has shown bees only begin to alter their investment strategies when a colony has at least 4,000 workers, but scientists haven’t been able to figure out how bees sense the size of their colony.

To solve the mystery, scientists at Cornell University tested the influence of three possible triggers on bee behavior: worker density, volatile pheromone levels and nest temperature. Researchers manipulated each of the three factors and measured how the changes affected the rate of drone comb building.

The tests showed neither temperature nor pheromones altered bee behavior. Scientists have previously hypothesized that changes in the types and concentration of pheromones — analogous to human hormones — explained bee puberty.

The new research, published in the Journal of Experimental Biology, showed worker density is the key factor. Scientists were able to trick workers into building more drone comb by squeezing them into more intimate confines.

“This tells us that density is important, but it doesn’t pinpoint how the workers assess worker density,” Michael Smith, neurobiology and behavior doctoral student at Cornell, said in a news release.

Follow up experiments showed increased contact with their nest mates and more uniform density throughout the nest serve as important cues for maturing worker bees.

“What interests me about this question, is that it’s the same problem faced by yeast, humans and colonies of social insects: Are you big enough to begin reproduction?” Smith said. “When it comes to a colony of social insects, it seems like they’ve shifted away from chemical cues, like hormones, and instead rely on physical ones.”

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