Monitoring of gas exchange cycles and ventilatory movements in the pine weevil Hylobius abietis: Respiratory failures evoked by a botanical insecticide

Abstract

The large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), is the most important insect pest of young coniferous plants. The implementation of new control methods requires not only a profound knowledge of the ecology and behaviour of the pest, but particularly of its physiology. Standard metabolic rate (SMR) and discontinuous gas exchange cycles (DGCs) were recorded in parallel with abdominal ventilation movements in adults of H. abietis using a differential electrolytic respirometeractograph. Quiescent weevils displayed DGCs of the constriction, flutter, and ventilation phases of the CFV type, while bursts of carbon dioxide were always accompanied by abdominal pumping movements, i.e., muscular ventilation in the closed subelytral cavity (SEC). In some beetles the C phase was absent and thus (C)FV cycles were recorded. In addition, at the beginning and often at the end of a burst, the SEC was rhythmically opened and closed by movements of the last abdominal segments. Continuous pumping movements and an absence of DGCs were signs of stress imposed by handling or by a new environment, even if the beetle was not moving. All individuals showed clear DGCs after recovering from handling and apparatus stress lasting 2-3 h. The results show that in the monitoring of DGCs, it is essential to determine whether they are of the constriction, flutter, and open phases (CFO), or the CFV subtype of the constriction, flutter, and burst (CFB) cycles. Use of our simple closed-system respirometer enables non-invasive simultaneous recording of SMR, oxygen uptake, DGCs, and active ventilation in H. abietis and other beetles. The topical application of adult H. abietis with sublethal doses of a botanical insecticide, NeemAzal T/S, caused essential respiratory failures: cyclic gas exchange was lost and irregular pumping movements appeared. In the treated beetles normal DGCs did not resume.