EUROPEAN JOURNAL OF ENTOMOLOGY

Eur. J. Entomol. 107 (4): 487-507, 2010 | DOI: 10.14411/eje.2010.057

A new look at discontinuous respiration in pupae of Hyalophora cecropia (Lepidoptera: Saturniidae): Haemocoelic pressure, extracardiac pulsations and O₂ consumption

Karel SLÁMA

Institute of Entomology, Biology Centre of Czech Academy of Sciences, Drnovská 507, 161 00 Praha 6, Czech Republic;

Discontinuous respiration in diapausing pupae of Cecropia silkworms was monitored by means of several electronic methods, including recording changes in haemocoelic pressure, monitoring respiratory movements by strain-gauge sensors and nanorespirographic recording of O₂ consumption and CO₂ output. It appears that, in contrast to previous concepts of stereotypic discontinuous respiration cycles (DGC) driven by accumulation of gaseous CO₂ in the body, the new results indicate that CO₂ remains dissolved in liquid carbonate buffers during interburst periods. In other words, there is no accumulation of gaseous CO₂ within the air filled tracheal space between the bursts. The bursts of CO₂ are caused by homeostatically regulated enzymatic hydration by carbonic anhydrase of metabolically produced carbonic acid. The chemically produced gaseous CO₂ was exhaled mainly by a bulk outflow through selectively opened or pulsating spiracles. The output of CO₂ was enhanced by actively regulated, unidirectional ventilation. The deep depressions in haemocoelic pressure, caused by permanent closure of all spiracular valves for long periods, appeared to be a specific feature of diapausing saturniid pupae. Physiologically, it has circulatory, not respiratory functions. The original definition of spiracular "fluttering" resulted from a misinterpretation of previously unknown extracardiac pulsations in haemocoelic pressure. The coordinated pulsation of the spiracular valves with extracardiac pulsations produce a very efficient, unidirectional ventilation of the whole tracheal system. According to the new results, the discontinuous respiration cycles of diapausing Cecropia pupae can be briefly described as follows: (1) Spiracular valves are kept permanently closed during the periods of deep depressions, they remain closed for some 99% of the time with occasional snap opening (passive inspirations) during prolonged interburst periods and more than 50% closed during the bursts; (2) During the long interburst periods, CO₂ is retained in liquid carbonate buffers, while the relatively high (after the burst) or low (toward the next burst) rate of O₂ consumption creates an internal vacuum, which is homeostatically compensated for by the snap-opening of one or just a few spiracular valves (passive suction inspirations); (3) The CO₂ gas, produced enzymatically by carbonic anhydrase, enters the air filled tracheal system and leaves the body by diffusion, a bulk outflow, or actively regulated unidirectional ventilation ("fluttering" spiracles). The selective advantage of this actively regulated respiratory system for water retention in pupae is discussed.

Keywords: Saturniidae, Hyalophora cecropia, respiratory acidaemia, haemocoelic pulsations, respiratory movements, O₂ consumption, spiracular pulsations, CO₂ bursts, chemically produced CO₂, carbonic anhydrase

Received: April 21, 2010; Revised: June 7, 2010; Accepted: June 7, 2010; Published: October 20, 2010  Show citation