Direct Measurement of PA:A=o2 in a Flying Bumble Bee with an Oxygen Micro Electrode.

A foraging bee is one of the most actively working insects. The bee's abdomen is well equipped with muscles for both contraction and extension. Besides, the bee has well developed air sacs not only in the abdomen but in the thorax. From view of the respiratory organ, a worker bee is a good example of a high oxygen consumed living thing. Here the gas transport system was investigated by measuring the oxygen partial pressure, Po2, in the bumble bee thorax. The measurement was made by directly inserting a needle electrode into a wing muscle. Results show the Po2 in a resting bee fluctuates with typically 70-120 sec interval. At phase of Po2 increase, the bee moved an abdomen repeatedly to ventilate air inside the body. The discontinuous ventilation should be beneficial for reducing water/heat loss but not necessary for oxygen supply at resting condition, therefore thermal effect to the ventilation pattern was examined, by which coiling a body changes the respiration from shallow to deep. In most case of the flight experiment, the bee started flying after elevating Po2 in the muscle by the abdominal movement, in that Po2 in the muscle decreased at onset of the flight. However, Po2 during flight gradually approaches the certain Po2 level which is much higher than the lowest value in the discontinuous ventilation. When the flight started without the preflight movement and Po2 was low in the muscle, Po2 inversely increased by the flight. To increase the oxygen supply during flight, the bee continuously contracted and extended the abdomen. The bee effectively uses the well equipped abdomen to take an advantage of the convective transport.