Heat can change a honey bee's hormone levels, but only if the bee is alone. New research from MSU entomologist Zachary Huang shows that isolated honey bees experience a rapid hormonal rise when exposed to high temperatures, while bees kept in groups stay stable. The discovery highlights how social conditions and chemical signals shape bees' ability to withstand environmental stress.
To test this, Huang and collaborator Thomas Rachman, a high school student when the experiments were conducted, exposed bees to one hour of heat at 40°C. They compared the effects of heat on solitary bees and on groups of 25, measuring how much juvenile hormone (JH) each produced under the same conditions. Juvenile hormones are present in all insects and are named for their role in keeping larvae "juvenile," preventing them from molting into adults. In adult honey bees, however, JH plays another role. It also helps pace behavioral shifts, with nurse bees showing lower levels of the hormone and foragers showing the highest levels.
In addition to testing with heat exposure, the researchers also wanted to understand whether the primer pheromone ethyl oleate, or EO, plays a role in this process. EO is naturally produced by forager bees and is known to influence the timing of a bee's transformation from a nurse to a forager. But until now, its potential role in stress resilience had not been explored. EO presumably suppresses the programmed increase of juvenile hormone (JH) in younger honey bees when foragers are present.
Results showed that isolated bees experienced a sharp rise in JH after heat exposure, while bees in groups did not. When solitary bees were exposed to EO inside EO‑treated vials, their hormone levels stayed normal — just like the grouped bees. These findings suggest that EO helps bees regulate their stress response and that social interactions may shield individuals from the physiological impacts of heat.
"Being social can make you cool!" Huang said. "We found a simple one-hour heating, only to 40°C (readily reached during summer, even in Michigan) will drastically raise honey bee workers' juvenile hormone titers, but remarkably, this only happens in solitary honey bees."
The work demonstrates how social insects may cope with rising global temperatures. If pheromones and group living help buffer bees from heat, colonies could be more resilient than previously understood.
The study also introduces a simple and effective way to examine stress responses in bees. The thermal stress assay Huang used opens the door for future investigations into how hormones and social behavior interact to strengthen colony resilience.
