The relations between the patterns of gas exchange and water loss in diapausing pupae of large white butterfly Pieris brassicae (Lepidoptera: Pieridae)

Abstract

The relations between the patterns of discontinuous gas exchange cycles (DGCs) and water loss were investigated in non- chilled diapausing pupae of the white cabbage butterfly Pieris brassicae kept at room temperature (22-24°C) in Petri dishes. An electrolytic respirometer, combined with an infrared (IR) actographic device was used for the simultaneous recordings of metabolic rate, cyclic release of carbon dioxide (bursts), passive suction inspirations (PSIs) and body movements. The patterns of cyclic gas exchange in four- and five-month-old non-chilled diapausing pupae varied individually to a considerable extent. About 40% of the pupae displayed long DGCs lasting 1-3 h, while the interburst periods were characterised by rare and almost regular large PSIs suc- ceeding at intervals of 1-4 min. Nearly 30% of the pupae exhibited short DGCs lasting 3-5 min, while between the bursts there occurred unclear frequent gas exchange microcycles. Standard metabolic rate (SMR) did not reveal significant differences between long DGCs and short DGCs ranging from 32-56 (mean 47.6 ± 4.6) ml O2 g -1 h -1 , and 28-61 (mean 44.95 ± 5.3) ml O2 g -1 h -1 , respec- tively. The mentioned levels of SMR were characteristic of diapausing pupae. Water loss in pupae with long DGCs was determined gravimetrically to be 0.29 ± 0.1 mg g -1 day 1 . At the same time, water loss in pupae that showed only short DGCs and irregular microcycles was 1.73 ± 0.31 mg g -1 day -1 , which was significantly higher than in individuals characterised by long DGCs. We suggest that water loss in the non-chilled diapausing pupae may depend significantly on the patterns of cyclic gas exchange: long cycles and rare but deep PSIs exerted a marked water conserving effect.