Roles of aorta, ostia and tracheae in heartbeat and respiratory gas exchange in pupae of Troides rhadamantus Staudinger 1888 and Ornithoptera priamusL. 1758 (Lepidoptera, Papilionidae)

In non-diapausing pupae of the two birdwing butterfly species Troides rhada mantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO2 release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three di fferent types of activity: Continuous forward-pulse periods of different du ration with a frequency range of about 0.25-0.52 s(-1), continuous backward -pulse periods with lower frequencies (0.15-0.29 s(-1)) and intermittent ba ckward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12-0.35 s(-1) alternated with heart pauses of 2-10 min. CO 2 release was discontinuous (CFO-type) from about four to 12 days after pup ation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO2 release rates were very low in both species (10-30 nmol g(-1) min(-1)). After this period, heart pauses occurred more frequently, p robably indicating the onset of metamorphosis and the beginning partial his tolysis of the heart. Infrared-optical and thermometrical measurements of h eartbeat indicated that haemolymph transport within the dorsal vessel in fo rward direction is more effective than in backward direction. This is deduc ed from the higher heartbeat frequency and heartbeat amplitude of the forwa rd pulsations. Results from ultrasonic doppler velocimetry suggest that hae molymph flow velocity is highest during the relatively long diastasis of 2- 3 s (30-40 mm s(-1)), while minimum particle speed (about 20 mm s(-1)) is a t the end of systole and the beginning of diastole. This would mean that ha emolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave meas ured with the infrared transmission technique was lower (about 8.4-22 mm s( -1) in Troides, 10-23 mm s(-1) in Ornithoptera) and remained constant durin g forward pulse periods. During backward beating the speed was lower (8-20 mm s(-1) in Troides, 9-17 mm s(-1) in Ornithoptera) and decreased during ba ckward pulse periods. During day two to seven in Troides and day three to n ine in Ornithoptera, spiracular opening periods coincided with changes in h eartbeat direction from backward to forward pulsations. A possible influenc e is the more efficient convective haemolymph mixing in the haemocoel durin g forward heartbeat. The mixing allows to bring the haemolymph in close con tact with the tracheal system where the discharge of CO2 takes place. Heart beat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles . (C) 1999 Elsevier Science Ltd. All rights reserved.