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A test is described which permits the determination of the respiratory rate of the insect to respond to, and recover from a short series of temperature changes. Both the transient and steady state respiratory responses were studied in the pupa, male and female of four species of tropical butterflies, Heliconius melpomene Linn., Papilio demoleus Wallace, Danaus chrysippus Linn., and Hypolimnas bolina Fabr., following a decrease and then an increase in environmental temperature.

Primary data consists of weight, oxygen consumption, and duration time of the transients; secondary data calculated from the above consisted of the Respiratory Change Ratio (RCR) and the % Recovery.

The RCR values were similar in pupa, male and female within a species, but showed significant differences between species, H. melpomene showing least change for a 10°C temperature change and H. bolina most. The ability to recover varied within and between species. In D. chrysippus there was no difference between pupa male and female; in H. bolina, pupa, male and female differed significantly in this. Heliconius melpomene showed very poor recuperative powers.

The most notable difference in the transients was the slow change following a drop in temperature compared with the instant increase to the steady state value following an increase in temperature. The duration of transients for body temperature were the same for both an increase and a decrease. The respiratory rate of the animal and its body temperature are clearly uncoupled during this period.

The transition of the respiratory rate associated with a decrease in temperature showed a smooth curve for the pupa but a momentary increase occurs in the adult.

A hypothesis is proposed to account for these results and their possible significance in the distribution and choice of a habitat by the butterflies discussed.