THERMOREGULATION IN COLONIES OF VESPULA ARENARIA AND VESPULA MACULATA (HYMENOPTERA: VESPIDAE) UNDER NORMAL CONDITIONS AND UNDER COLD STRESS

Abstract

Captive colonies of Vespula arenaria (Fabricius) and Vespula maculata (Linnaeus) were placed in the field during the summer and fall of 1972. The adults were free to forage, and the colonies developed normally. Nest temperatures were recorded at mid-afternoon, 6 days per week. Once each week, colonies were confined, brought into the laboratory, and placed in a cold room at 5 °C for 4 h. At the end of this period, the nest temperatures were recorded and the colonies returned to the field. Under field conditions, V. arenaria colonies maintained an average daytime nest temperature of 31 °C, and V. maculata colonies maintained an average daytime nest temperature of 29 °C. As they developed, colonies of both species were increasingly capable of resisting cooling at an ambient temperature of 5 °C. This ability to thermoregulate under extreme conditions peaked in early August for V. arenaria and in late August for V. maculata. In both species, the decline in the ability to thermoregulate was associated with the production of reproductives. It appears that the major function of thermoregulation in these two species is to provide a favourable temperature for the development of the young rather than to provide the colony with protection against low ambient temperatures.