THERMAL-BEHAVIOR OF ROUND AND WAGTAIL DANCING HONEYBEES

The thermal behavior of round and wagtail dancing honeybees (Apis mell ifera carnica) gathering sucrose solutions of concentrations between 0 .5 and 2 mol . l(-1) was investigated under field conditions by infrar ed thermography (30-506 m flight distance). During the stay inside the hive thoracic surface temperature ranged from 31.4 to 43.9 degrees C. In both round and wagtail dancing honeybees the concentration of sucr ose in the food influenced dancing temperature in a non-linear way. Av erage dancing temperature was 37.9 degrees C in foragers gathering a 0 .5 mol . l(-1) sucrose solution, 40.1 degrees C with a 1 mol . l(-1), 40.6 degrees C with a 1.5 mol . l(-1) and 40.7 degrees C with a 2 mol . l(-1) solution. The variability of thoracic temperature was highest with the 0.5 mol . l(-1) and lowest with the 1.5 and 2 mol . l(-1) con centrations. Thoracic temperatures during trophallactic contact with h ive bees were similar to dancing temperature at 1.5 mol . l(-1) but lo wer at the other concentrations. During periods of distribution of foo d to hive bees (trophallactic contact >2.5 s) the dancers' thorax cool ed down by more than 0.5 degrees C considerably more frequently with t he 0.5 mol . l(-1) solution (65% of cases) than with the 1.5 mol . l(- 1) solution (26%). By contrast, heating the thorax up by more than 0.5 degrees C was infrequent with the 0.5 mol . l(-1) solution (2%) but o ccurred at a maximum rate of 26% with the 1.5 mol . l(-1) solution. Be es gathering the 1 or 2 mol . l(-1) solutions showed intermediate beha vior. Linear model analysis showed that at higher concentrations the d ancers compensated better for variations of hive air temperature: per 1 degrees C increase of hive temperature dancing temperature increased by 0.34, 0.22, 0.12, and 0.13 degrees C with 0.5, 1, 1.5, and 2 mol . l(-1) sucrose solutions, respectively. The results furnish evidence t hat dancing honeybees follow a strategy of ''selective heterothermy'' by tuning their thermal behavior to the needs of the behavior performe d at the moment. Thoracic temperature is regulated to a high level and more accurately when fast exploitation of profitable food sources is recommended. Thoracic temperature is lowered when the ratio of gain to costs of foraging becomes more unfavorable.