Oscillating haemolymph ?circulation? and discontinuous tracheal ventilation in the giant silk mothAttacus atlas L.

Abstract

1. In the mothAttacus atlas (Saturniidae) an oscillating haemolymph ‘circulation’ and its coordination with tracheal ventilation are described. Periodic heartbeat reversal, intermittent backward haemolymph flow through the perineural sinus and two different superimposed modes of abdominal movements are analyzed by means of contact thermography and photocell measurements. 2. Intraperiodic fluctuations and age dependent alterations in heartbeat frequency and duration of pulse periods are discussed with respect to changes in haemolymph volume and haemocoele capacity. 3. The frontal aortal sac shows transport activity only during the forward pulse period of the heart; during the backward pulse period the amount of haemolymph in the head is reduced. The aorta continues to pulse in the freshly severed head. 4. The expiratory air flow at the spiracles and spiracular valve closing were investigated. In the anterior part of the body expiration occurs slowly as a consequence of haemolymph accumulation during the forward pulse period of the heart, while inspiration takes place as a consequence of removal of haemolymph from the anterior body into the abdomen during a backward pulse period. When most haemolymph is accumulated in the abdomen, expiration of the abdominal tracheal system is accomplished by bouts of abdominal peristaltic movements. The latter are aided by coordinated closing of the abdominal spiracular valves. 5. Transient haemolymph pressure increase by ventilatory movements is probably restricted to the abdomen by a septum and valve in the anterior abdomen. This compartmentation of the adult lepidopteran body combined with haemolymph oscillation is suggested to be a principle advantage in optimal utilization of a small haemolymph quantity with regard to tracheal ventilation in flight-adapted, light-weight construction.