Metabolism and upper thermal limits of Apis mellifera carnica and A. m. ligustica

The Western honeybees Apis mellifera carnica and A. m. ligustica are closely related subspecies living in neighbouring regions. Metabolism and the upper lethal thermal limits are crucial physiological traits, adapted in the evolutionary process to environment and climate conditions. We investigated whether samples from these two ecotypes differ in these traits. The standard metabolic rate was higher in the A. m. ligustica population only at a high temperature (T (a) ~ 40 °C; dVCO(2) = 12 nl s(−1); P < 0.05), probably due to a higher body temperature (dT(thorax) = 1.5 °C; P < 0.01). The critical thermal maximum of activity and respiration was similar (difference activity CT(max) = 0.8 °C, respiratory CT(max) = 1.1 °C). The lethal temperature (LT(50, 8h)) revealed higher tolerance and survival rates of the Ligustica bees (Carnica 50.3 °C; Ligustica 51.7 °C; P < 0.02). Results reveal the adaptation of the two subspecies to their historic climate conditions, possibly favouring Ligustica in a warming environment.