Short-term changes in juvenile hormone titers in honey bee workers due to stress

Abstract

Juvenile hormone (JH) is well studied in honey bees because it regulates caste determination in immatures and division of labor in adult workers. However it is not clear whether JH titers change significantly under stresses commonly experienced by workers in experimental manipulations. In this study we determined the effect of caging and cold-anaesthesia on JH titers in both nurses and foragers. The JH titers of nurses and foragers kept in cages at room temperature, or anaesthetized on ice, for up to 24 hours were determined at various time intervals. Nurses displayed a significant and sustained increase in JH titers by 1-2 hours in 2 out of 3 colonies, regardless whether being cold-anaesthetized or caged. Nurses in 4 out of 4 colonies showed remarkable JH titer elevations 24 hours after being caged. The increase ranged from 3-142 fold compared to their initial baseline JH titers. In foragers, changes in JH titers depended on their initial JH titers: foragers with low JH titers increased while those with high JH titers decreased. These results suggest that nurses and foragers respond to stress differently. The fact that JH did not always increase under stress conditions suggests that JH apparently does not function as a "stress-hormone" in honey bees under the two conditions we studied.