Temperature Regulation and Energetics of the Solitary Bee Centris pallida during Foraging and Intermale Mate Competition

Solitary bees (Centris pallida Fox; Hymenoptera: Anthophoridae) were observed during diurnal activity in a hot desert environment. Females foraged throughout the day in flowering paloverde trees; males divided their time between foraging and hovering in search of receptive females. Thoracic temperatures (Tth) of both sexes were high. Foraging males and females had Tth averaging 44–46 and 43–45 C, respectively. The Tth of hovering males averaged about 44 C in the early morning and 47 C from midmorning until activity ceased. Thoracic temperatures of both sexes changed by 3–4 C over an ambient temperature (Ta) range of 25–40 C. Abdominal temperature (Tab) was consistently about 4.5 C above Ta, and there was no indication of augmented heat transfer between thorax and abdomen at high Tth. Maximum tolerable Tth was 50–51 C. Evidence for evaporative heat loss was equivocal for artificially heated bees, but free-flying animals showed little indication of use of evaporative cooling. Energy metabolism (measured as oxygen consumption) during flight (1. 1 W/g thorax) resembled that of other endothermic insects of similar mass; mass-specific thermal conductance (0.034 W/[g thorax - C]) was slightly larger than predicted from body mass. Centris pallida probably controls body temperature by reducing flight at high Ta. Nevertheless, hovering males often attain Tth within 2–3 C of lethality.