Colony density, not hormones, triggers honeybee 'puberty'

May 5, 2017 by Linda B. Glaser

New research helps answer a long-standing mystery of how honeybees sense the size and strength of their colony, a critical cue for the bees to switch from investing solely in survival to also investing in reproduction.

In a paper published May 3 in the Journal of Experimental Biology, a Cornell-led research group reports on how workers detect that their colony has reached a threshold to invest in a special type of reproductive comb.

In honeybees, the first sign that a colony can "afford" to invest resources in reproduction, as opposed to making investments only in survival and growth, is when workers begin to build a special type of beeswax comb, drone comb, used for rearing drones (reproductive males). Like pubescent humans, a colony that is building drone comb is not yet fully reproductive, but its workers have detected that the colony is strong enough to begin investing resources into reproduction for use in the future. Bees only begin building drone comb once their colony has enough workers, about 4,000. But how do the workers detect that their colony is large enough?

The researchers – neurobiology and behavior doctoral student Michael L. Smith, Phoebe A. Koenig '16, and Harvard University doctoral student Jacob M. Peters – experimentally tested the effect of three possible cues that would trigger bees to begin constructing cells of beeswax comb used for rearing drones. These potential signals included worker density, volatile pheromone concentration and nest temperature. After experimentally increasing each of these cues, they measured how much drone comb the bees then built. They found that only increasing worker density induced workers to build a higher proportion of drone comb relative to a control. Both higher temperature and higher concentration of volatile pheromones had no effect on the colony's comb building.

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