Direct measurement of oxygen partial pressure in a flying bumblebee.

The gas transport system of a bumblebee was investigated by measuring the oxygen partial pressure P(O(2)) in the wing muscle. In the resting bee, P(O(2)) showed a regular pattern of fluctuation with a typical period of 70-120s. Fluctuations in muscular P(O(2)) were associated with intermittent abdominal pumping. Ventilation by abdominal movements may not be necessary during rest because P(O(2)) is high (8.5-9.2kPa) in the anaesthetised bee. Thermal effects on muscular P(O(2)) were examined by cooling the bee, causing the amplitude of P(O(2)) fluctuations to increase. In most flight experiments, the bee started to fly after elevating muscle P(O(2)) by abdominal pumping; muscle P(O(2)) then decreased at the onset of flight. However, when a flight began without pre-flight ventilation, P(O(2)) increased monotonically. During flight, muscle P(O(2)) reached a mean level (6.36+/-1.83kPa) that was much higher than the lowest value recorded during discontinuous ventilation during rest. The bumblebee effectively uses abdominal movements to assist in convective gas transport not only during flight but also at rest.