Endothermy and thermoregulation in solitary bees

This thesis examines the roles of endothermy and body size in the thermal biology of solitary bees (Hymenoptera: Apoidea) within the species Anthophora plumipes (Anthophoridae) Amegilla sapiens (Anthophoridae) and Creightonellafrontalis (Megachilidae), within the genus Anthophora, and over the Apoidea as a whole.
The effects of body size, climate and sexual interactions on the biology of Anthophora plumipes were investigated in Oxford between 1987 and 1989. Both ambient temperature and body size had a significant effect on females' ability to forage, what time they initiated foraging in the morning, and the type and mass of provisions collected. The behaviour of males was also strongly dependent on ambient temperature, which affected not only when they emerged from their nest tunnels, but also how long they spent basking, when and where they fed, and whether they showed courtship behaviour.
The activity patterns and behaviour of male and female A. plumipes over time were shown to correlate with a complex array of factors. Activity patterns of females depended on the quality of floral resources available at foraging sites, body mass, ambient temperature, the position of the female in her nest-provisioning cycle, and levels of male interference at foraging sites. Male behaviour not only depended on body size and ambient temperature, but also on which other bees (particularly male and female conspecifics) were encountered while patrolling food sources and at the nest site.
Endothermy in bees is much more widespread than previously thought, and warm-up before flight was present to some degree in all the species examined. Levels of thermoregulation achieved, however, varied considerably between species. Warm-up rates in bees, and thoracic temperatures in free and tethered flight, are shown to depend on ambient temperature and body mass within a species (for temperate and tropical examples), across members of the genus Anthophora and across the Apoidea as a whole. The persistence of these relationships over a range of comparative levels suggests that they are of fundamental importance. The form of these relationships differs between families in the Apoidea, and significant patterns only emerge when a comparative technique controlling for phylogeny is applied. Furthermore, body temperatures may also depend, in at least some cases, on sex and there may be differences within a group of related species between provisioning and parasitic forms. The interaction of all these factors is complex, and the predictive value of a variable such as body mass does not always emerge unless sophisticated techniques are used to control for other variables.
The errors associated with two common methods in the measurement of insect body temperatures have often been loosely discussed but rarely quantified. This thesis examines (a) the magnitude and possible effects of errors in 'grab-and-stab' measurement of body temperature, and (b) the errors in measurement of body temperature using fixed sensors linked by thermally conducting leads to measuring devices. In neither case do the demonstrated errors preclude use of the technique, but care with interpretation is required. In both cases, measurement of thoracic temperature in small bees involves the largest errors, and this is the most serious obstacle to comparisons of endothermic and thermoregulatory abilities over the full range of body sizes found in the Apoidea.

Advisor: Willmer, P