Effect of food quality on the body temperature of wasps (Paravespula vulgaris).

Body surface temperature of individually marked wasps (Paravespula vulgaris, Vespidae, Hymenoptera) was measured by infrared thermography during repeated visits to a feeding bowl without injuring them or disturbing their behavior. Wasps were fed 0.5, 1 and 2 mol/l sucrose solution at two ambient temperatures.Thoracic temperature varied significantly in dependence on food quality (sucrose concentration of solution). At the higher ambient temperatures of 26.1-30.2 degrees C mean thoracic surface temperatures from different experiments were 35.3 and 38.0 degrees C when the wasps took a 0.5 mol/l sucrose solution, 37.0, 38.7 and 38.7 degrees C when they took a 1 mol/l solution, and 39.1 degrees C when they took a 2 mol/l sucrose solution. At the lower ambient temperatures of 17.6-21.0 degrees C thoracic temperatures were lower but the effect of different sucrose concentrations was similar: 34.7 degrees C with a 0.5 mol/l and 36.1 degrees C with a 1 mol/l sucrose solution. The concentration effect amounted to about 10-25% of the whole variability of thorax temperature. By contrast, the temperatures of the head and abdomen did not follow the changes in thorax temperature according to changes in sucrose concentration closely, which suggests that the pattern of haemolymph circulation may have changed after landing, during the wasps' stay at the feeder. At initial landing at the feeders thoracic temperatures where equal to (three of eight tests) or lower (five of eight tests) than at final departure.The correlation of thorax temperature with food quality probably reflects the wasps' level of excitement and motivation to collect the food, which allows them to balance energetic investment with profitability of foraging and the needs of flight muscle performance and motility.