Heat loss from colonies of bumblebees: mechanisms and consequences

Abstract

Pollinating insects provide ecosystem services worth billions of dollars globally and the pollination of crop plants is vital for food security. Declines in pollinating insects have been associated with a variety of anthropogenic drivers of change. With a global population expected to reach nine billion by 2050 a better understanding of the relationship between agroecosystems and pollinators is required to maintain food security. Bumblebees are important pollinators that utilise efficient thermoregulation to develop their colonies. Heat loss by convection, conduction and radiation are potential obstacles to thermoregulation. Insulation limits heat loss and so behaviours of bumblebees that mitigate heat loss could have high adaptive significance. This thesis aimed to identify the relative importance of convection, conduction and radiation as mechanisms of heat loss from bumblebee colonies. Secondly, model the impacts of shortfalls in incubation on colony fecundity. Microcolonies of six orphaned worker bumblebees were used to the effect of different types of insulation of thermoregulation. Sugar consumption and average brood temperature were measured in order to determine the effects of different types of insulation, which allows insight into the mechanisms of heat loss in bumblebee nests. Developmental and demographic models were used to investigate the relationship between brood temperature on developmental time and colony fecundity in bumblebees. The results presented here show that heat loss by radiation is likely to be a small obstacle to thermoregulation in bumblebee nests. In contrast, insulation to reduce heat loss by convection and conduction resulted in higher average brood temperatures with no difference in syrup consumption compared to uninsulated boxes. Modelling revealed that queen production is highly sensitive to relatively small drops in average brood temperature. For example, a one degree reduction in average brood temperature from approximately 27.2⁰C to 26.2⁰C could result in an 11.4% reduction in queen production. The impact of nest thermoregulation on queen production highlights the adaptive significance of nesting behaviours, both the initial nest site choice by the queen and insulation behaviours of workers. The results of the model on the effect of temperature on colony fecundity demonstrate the mechanism by which shortfalls in incubation could reduce colony fecundity and result in declines in bumblebee populations.