Lifelong patterns of forager behaviour in a tropical swarm-founding wasp: effects of specialization and activity level on longevity

Abstract

The relationships between foraging tenure and specialization on materials, and foraging tenure and foraging activity were measured for marked, known-age workers of the social wasp Polybia occidentalis. The purpose of the study was to assess differences in cost to foragers, in terms of risk of mortality, associated with material specializations and activity level, and determine whether ontogenetic changes in forager behaviour reflect these differences in cost, such that more risky patterns of behaviour are postponed until later in adult life. Polybia occidentalis workers terminated foraging at an average of 5·9 days after their first trip, independent of their age at first foraging, suggesting that this task entailed a high risk of mortality. Lifetime foraging activity was calculated as foraging rate (mean number of trips per hour), foraging effort (mean number of time-weighted trips per hour), and as the proportion of observation days that an individual was active during her foraging tenure. Foraging tenure was not related to foraging rate or effort, but had a strong negative relationship with the proportion of observation days during which an individual foraged. By the latter measure, risk of mortality increased with foraging activity. The length of foraging tenure was negatively correlated with the proportion of foraging effort devoted to food materials (nectar and insect prey), supporting the hypothesis that gathering food was riskier than gathering nest materials (water and wood pulp). Foragers that switched between food and nest materials exhibited no tendency to specialize on nest materials first and therefore foraging for riskier materials was not always performed later in adult life. These results are discussed in terms of possible factors regulating task performances at the individual level in social insects.