Changes in the discontinuous gas exchange cycle (DGC) of pupal Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) over developmental age and at several temperatures were examined. Both Bacillus thuringiensis susceptible and resistant strains of beet armyworm were used. Flow through respirometry was conducted using 1 to 7 day old pupae. In both treatment groups, there was a significant difference P<0.05 in the amount of CO2 produced during pupal development. There was an increase in CO2 production early in pupal life followed by a minimum at mid-pupal and an increase at late-pupal development. In the resistant strain, the open phase made up 22% of the entire cycle compared with 19% in the susceptible strain. However, in both strains the percentage of the close and flutter phases (~40%) were significantly different from the open phase (~21%). In both strains, distinct cycles (close, flutter, and open phases) were produce at 10oC however, at lower temperatures of about 5oC there were no cycles just continuous CO2emission while continuous cycles were observed at higher temperatures. This study emphasizes the need to use insects of the same developmental age in any study of insect respiration pattern and energy metabolism. Also, our results do not support the theory that DGC originated as a mechanism for water conservation because at higher temperatures where water loss is greater, pupae did not show DGC instead this was observed at lower temperatures with the least water lose.
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