Effect of the presence of brood on the behavior and nutrient levels of emerging individuals in field colonies of Polistes metricus

Abstract

Caste determination in social insects with morphologically distinct castes occurs during a critical period during the larval stage. In contrast, in social insects without morphologically distinct castes the time of eclosion can act as an additional critical period. A number of cues have been identified that influence caste differentiation in social insects but to date, most of the studies have used physiological correlates to determine the effects of these cues on caste determination. Few studies have measured behavioral differences in a natural setting. In this field study, the behavioral and nutritional profiles of individuals of the paper wasp Polistes metricus emerging on nests with and without larvae were determined and compared to emerging workers and gynes from unmanipulated colonies. Based on previous studies, it was predicted that individuals eclosing on nests with larvae would have similar profiles to workers and those eclosing on nests without larvae would have similar profiles to gynes. Individuals that emerged on colonies with larvae had similar behavioral and nutritional profiles to workers as expected. Individuals that emerged on nests without larvae had behavioral and nutritional profiles that were in between workers and gynes and showed signs of active reproduction and nest construction. The results of this study were combined with those of other studies into a model that proposes that there are three thresholds, one in response to photoperiod, one during the larval stage, and one during eclosion that determines if individuals will be workers, active reproducers, or overwintering gynes. This model provides a more complete picture of caste determination in Polistes.