The control of nest climate in bumblebee (Bombus terrestris) colonies: interindividual variability and self reinforcement in fanning response

Interindividual variability in response to environmental stimuli is believed to have a major impact on collective behaviors in social insects. The present study presents a detailed investigation of the variability in individual fanning behavior underlying the collective control of nest climate in bumblebee (Bombus terrestris) colonies. Four colonies were repeatedly exposed to increasing temperature and CO2 levels. The response threshold of each worker (defined as the mean stimulus intensity at which a worker responded by fanning) was determined. Temperature response thresholds of 118 workers and CO2 response thresholds of 88 workers were analyzed. Workers differed in their response thresholds. Some consistently responded to low stimulus intensities, others consistently responded to high stimulus intensities. No consistent correlation between temperature and CO2 thresholds was found within individuals. Response thresholds of fanning bees decreased over successive trials, providing empirical support for the idea of specialization through individual threshold reinforcement. In addition to variability in individual response thresholds, workers of a colony differed in two other parameters of responsiveness: response probability (the probability of responding to a stimulus once it exceeded an individual's response threshold) and response duration (the persistency with which fanning was performed once an individual responded). The results of the present study suggest that response threshold, response probability and response duration are important independent parameters of individual responsiveness in the collective control of nest climate in bumblebee colonies.