Meeting Abstract

P2.157  Monday, Jan. 5  The effects of continuous and discontinuous gas exchange cycles on CO₂ and H₂O production. WILLIAMS, C.M.**; SINCLAIR, B.J.; University of Western Ontario, London, Ontario; University of Western Ontario, London, Ontario cwilli67@uwo.ca

When investigating insects that show a variety of patterns of respiration, it can be very difficult to objectively choose a representative portion of a respiration trace to evaluate. Erynnis propertius (Lepidoptera:Hesperidae) overwinters in diapause as a caterpillar, during which time they show both continuous respiration and discontinuous gas exchange cycles (DGC). This provides an opportunity to investigate the effects of sample selection and pattern of respiration on measured CO₂ and H₂O production and estimated metabolism. CO₂ and H₂O production by diapausing E. propertius caterpillars (n=20) was recorded for four hours at 1 and 8 C after a three hour acclimation period, and all analyzable sections of data were compared. At 8 C, 40.5 % of individuals showed solely continuous respiration and 47.6 % solely DGC; but 11.9 % of individuals switched between patterns during the four hour period. In individuals that had more than one complete discontinuous cycle, CO₂ production did not change over time; however H₂O loss declined throughout the trace. There was no effect of mode of respiration (continuous or DGC) on CO₂ production, but H₂O loss was significantly lower during DGC. All individuals showed continuous respiration at 1 C, which we attribute to the onset of chill coma. We discuss these results with regards to the evolution of DGC and suggest some guidelines for determining standard metabolic rate in insects that exhibit a combination of gas exchange patterns.