Direct measurement of oxygen partial pressure in a flying bumblebee

Abstract

The gas transport system of a bumblebee was investigated by measuring the oxygen partial pressure PO2 in the wing muscle. In the resting bee, PO2 showed a regular pattern of fluctuation with a typical period of 70-120 s. Fluctuations in muscular PO2 were associated with intermittent abdominal pumping. Ventilation by abdominal movements may not be necessary during rest because PO2 is high (8.5-9.2 kPa) in the anaesthetised bee. Thermal effects on muscular PO2 were examined by cooling the bee, causing the amplitude of PO2 fluctuations to increase. In most flight experiments, the bee started to fly after elevating muscle PO2 by abdominal pumping; muscle PO2 then decreased at the onset of flight. However, when a flight began without pre-flight ventilation, PO2 increased monotonically. During flight, muscle PO2 reached a mean level (6.36±1.83 kPa) 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.