AN EXPERIMENTAL ANALYSIS OF THE DISCONTINUOUS RESPIRATION OF THE CECROPIA SILKWORM

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Abstract
Respiration of diapausing Cecropia pupae is remarkable in that metabolic CO2 is retained within the insect and released during brief periods as "bursts". This finding confirms Pun''s prior observations on several spp. of diapausing insects. At 25[degree] C in 14 pupae with an average weight of 4.7 g, bursts of CO2 occurred on the average of once every 7.3 hours and the burst volumes averaged 271 mmVanimal. Average interburst rate of CO2 output was 2.7 mm3/g live weight/hour, i.e., about 1 the average rate of O2 uptake. Utilization of O2, unlike the release of CO2, shows no discontinuities and "direct" Warburg manometric procedures reveal an apparently continuous uptake of O2. Several independent lines of experimentation confirm the manometric observations that O2 uptake by the pupa is continuous and non-cyclic and direct attention to the surprising fact that, in the interburst period, O2 may enter the insect at many times the rate at which CO2 makes exit. Virtually all respiratory exchange ceases after the spiracles are sealed with wax; the tracheal system and spiracles are therefore the site of both the discontinuous release of CO2 and the simultaneous continuous uptake of O2. The cycle of CO2 release is a function of metabolic rate and therefore of temperature. At low metabolic rates the bursts are accentuated. Thus, at 10[degree] C CO2 is given off only once in several days and the interburst rate of CO2 output may be but l/100th the rate of O2 uptake. If the insect''s metabolism is increased by integumentary injury, or development, or increase in environmental temperature, the bursts become more frequent and the continuous release of CO2 more pronounced. The burst phenomenon usually disappears when the O2 uptake rises beyond 160 mm3/g live weight/ hour. Bursts also vanish when the external O2 tension is decreased below 15% or the external CO2 increased above 10%. Interburst rate of CO2 output is especially sensitive to O2 tension and in pure O2 the interburst CO2 output may become undetect-able. For bursts of equal volume, the rate of release of CO2 during the burst is substantially the same at 10[degree] and 25[degree] C, signifying that the rate-limiting processes in the rapid release of CO2 are of a physical character with low temperature coefficients. The discontinuous release of CO2 is apparently a widespread phenomenon in diapausing pupae. This fact complicates determinations of respiratory quotients and is evidently responsible for the extremely low and apparently erroneous values reported for diapausing popae.