Changes in response thresholds with age in workers of the ant, Pseudomyrmex pallidus

The tendency of a worker to perform a particular task in social insect colonies has been linked to its response threshold for task-related stimuli. Individual workers display temporal polyethism, progressing through a suite of tasks as they age. This phenomenon leads to the possibility that response thresholds to various task related stimuli may change as a worker ages. The response thresholds of workers of the ant Pseudomyrmex pallidus to ascending concentrations of sucrose solution, cricket extract, brood pheromone and foreign adult cuticular hydrocarbons (CHCs) were measured at five day intervals to determine how response thresholds change with age. The behavior of each ant was also monitored to see if changes in response thresholds were correlated with age-related task changes. Antennal stimulation by sucrose solution, cricket extract and brood pheromone induced a tethered worker to close her mandibles completely followed by extension of her hyperglossae. Application of CHCs to the antennae induced an aggressive mandible opening response. This work was motivated by preliminary research which demonstrated that in-nest workers had a significantly higher response threshold to sucrose solution and brood pheromone than foragers, and were also on average younger than foragers.