TEMPERATURE AND THE POLLINATING ACTIVITY OF SOCIAL BEES

1. Thermal constraints on flight acivity limit the pollinating effecti veness of bees. Each species of social bee has a microclimatic 'window ' within which foraging flight can be sustained. 2. To predict whether a given species of social bee is worth testing as a pollinator in a g iven climate, it is useful to know at least the lower limits of that m icroclimatic 'window'. We consider how information from a series of be e counts through a day can be used to characterize a bee species in te rms of activity/microclimate relations as a basis for predicting the d iel pattern of foraging activity of a bee introduced into a new climat e as a pollinator. 3. We discuss the relative merits of bee counts at a foraging patch and counts based on hive traffic as indices of the pr oportion of bees active. 4. We suggest that the activity/microclimate relations of a species be expressed in terms of the lower threshold bl ack globe temperature for flight activity. Black globe temperature, T( g), is easily measured with inexpensive equipment, and can substitute for measurements of ambient temperature and radiation as a predictor o f diel patterns of bee activity. 5. We use examples of field data to e xplore the relationship between microclimate and activity for the hone ybee Apis mellifera and several species of bumblebee, Bombus. Regressi on analysis is used to relate activity to T(g) and to identify the low er temperature threshold for activity from field bee counts. 6. In fie ld studies analysed here, the bumblebees Bombus terrestris/lucorum, B. pascuorum and B.hortorum began foraging at lower temperatures than hon ey-bees or B.lapidarius.