Sibul, I., Kuusik, A. Luik, A. and Ploomi, A. 2008. Active Tracheal Ventilation and its Metabolic Cost in the Large Pine Weevil, Hylobius abietis(L.) (Coleoptera: Curculionidae). Baltic Forestry 14(2):131-137

The large pine weevil, Hylobius abietis (L.) is the major damaging insect pest in reforestation areas in coniferous forests in Europe. New control methods require deep knowledge of the ecology, behaviour and also physiology of the pest. A study of respiration pattern was conducted to determine the metabolic cost of active ventilation in adults of the large pine weevil, Hylobius abietis. A volumetric-manometric respirometer was used in parallel with an infrared opto-cardiograph to record muscular contractions together with gas exchange patterns.
In the dry insect chamber, i.e. in the dehydrated conditions the pine weevil displayed discontinuous gas exchange cycles (DGCs). Most of the DGCs were of CFV (Closed-Flutter-Ventilation) type, where bursts of carbon dioxide release (V phase) were ventilated by abdominal pumping movements. However, about 10% of the bursts in each individual were not ventilated. In the ventilated cycle the burst volume (VCO2) was about 20% greater than that of the non-ventilated cycle, suggesting a significant metabolic effect of pumping movements.
A minority (ca 10%) of dehydrated individuals exhibited DGCs of CFO (O=open) type, where pumping movements were lacking, and in these individuals the level of metabolic rate was about 20% lower than in weevils characterised by CFV cycles. The CFO cycles in H. abietis were considered as an exceptional and unfavourable event. Nevertheless, the results suggested that in individuals of H. abietis showing complete tonic immobility (CFO cycles) the levels of the true standard metabolic rate (SMR) were measured.
DGCs recorded by means of flow through method i.e. by infrared gas analyzer (IRGA), were usually recognized as signs about the existing standard metabolic rate in an insect. Our results indicated that DGCs appearing in dry air in pine weevils are a sign of standard metabolic rate only in case of CFO cycles, where muscular contractions are absent. In weevils showing CFV cycles can not be measured the level of standard metabolic rate due to the vigour active ventilation by means of abdominal pumping movements. Thus, IRGA can not be regarded as an universal method to differentiate the active and standard metabolic rates. Moreover, in parallel with respirometer must be used an actographic device, to record all body movements including abdominal pumping movements.

Key words: CFO and CFV cycles, discontinuous gas exchange cycles, DGC, Hylobius abietis, large pine weevil, standard metabolic rate