The effect of ambient humidity and metabolic rate on the gas-exchange pattern of the semi-aquatic insect Aquarius remigis

We have examined the effects of temperature on metabolic rate and respiratory pattern in the water strider Aquarius remigis. As temperature was increased from 10 to 30 degrees C, the metabolic rate of the insects increased and the respiratory pattern transitioned from discontinuous, to cyclic, to continuous. The discontinuous gas-exchange cycle (DGC) was observed even in insects standing on water when the respirometry chamber was being perfused with humid (> 95% relative humidity) air. Comparisons of insects at 20 degrees C in humid and dry air showed no statistically significant differences in metabolic rate or respiratory pattern (P > 0.05). The proportion of time that the spiracles were closed was greater at 10 degrees C than at 20 degrees C (P < 0.01), and greater at 20 degrees C than at 30 degrees C (P < 0.05). These results are compatible with the hypothesis that the respiratory patterns of insects are determined by the relationship between oxygen supply and oxygen demand. There was no evidence in this insect that humidity had any effect on the respiratory pattern. The results are discussed in the context of the ongoing discussion in the literature of the origin, maintenance and adaptive significance of the DGC in insects.