Circulation - Ventilation Cycle

Bees respirate by telescoping their abdomen in and out, creating positive and negative pressure which pushes the air out and then draws the air into the air sacs These abdominal pumping movements are related to the heart beats at high thoracic temperatures but not at low thoracic temperatures (Heinrich, 1976).

At high thoracic temperatures, for every telescoping movement of the abdomen there is one ventral diaphragm contraction and one heart beat. When the abdomen contracts (expiration) the air in the abdomenal air sac and the blood are forced through the petiole into the thorax simultaneously. This pushes the ventral diaphragm down, temporarily sealing off the flow of the venous blood through the petiole. When the air and blood have passed into the thorax, the ventral diaphragm can contract (inspiration) as the abdomen expands. It creates a channel through which pulses of venous blood are released into the abdomen via the petiole.

The flow of the arterial and venous bloods alternate at high thoracic temperatures so that heat can be dumped into the abdomen by avoiding the countercurrent exchange. Dumping heat into the abdomen can help lower the thoracic temperature to prevent overheating (Heinrich, 1976)

At low thoracic temperatures, the abdomen pumps at a low frequency or not at all. The heart beats and ventilatory movements of the abdomen have no relation, except when the heart has a high amplitude beat, then they occur together. Because the ventilation is independent of the heart beats, the countercurrent heat exchange is not interrupted. Normally, the heart beats weakly and at a high frequency so the heat exchange is facilitated (Heinrich, 1976).

diagrams adapted from Heinrich, 1976