© 2004 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 110: 173 – 179, 2004 173 Blackwell Publishing, Ltd. Monitoring of gas exchange cycles and ventilatory movements in the pine weevil Hylobius abietis: respiratory failures evoked by a botanical insecticide I. Sibul 1, *, A. Kuusik 2 & K. Voolma 3 1 Faculty of Forestry, Estonian Agricultural University, Kreutzwaldi 5, EE51014 Tartu, Estonia; 2 Institute of Plant Protection, Estonian Agricultural University, Kreutzwaldi 64, EE51014 Tartu, Estonia; 3 Forest Research Institute, Estonian Agricultural University, Kreutzwaldi 5, EE51014 Tartu, Estonia Accepted: 6 November 2003 Key words: electrolytic microrespirometer, insect respiration, muscular activity, active ventilation, CFV and (C)FV cycles, DGC, NeemAzal T/S, Coleoptera, Curculionidae 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 pro- found 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 respirometer- actograph. 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 move- ments, 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. Introduction The large pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae), is the most important insect pest of young coniferous plants in the northern part of Eurasian coni- ferous forests. Feeding adult weevils girdle and kill millions of planted coniferous seedlings each year, causing enormous economic losses (Örlander & Nilsson, 1999). Various chemical insecticides have been used against the large pine weevil. The growing threat of environmental contamination and a prohibition on the use of chemical insecticides in forests in many countries have encouraged the conducting of experiments with various biological insecticides (Luik et al., 2000; Sibul et al., 2001, 2002) in order to reduce the extensive damage caused by pine weevils in forest plantations, as well as to protect the environment. At the same time, the implementation of new alternative control methods and the introduction of biological insecticides requires profound knowledge of not only the ecology and behaviour of the pest but particularly of its physiology (Merivee et al., 1998; Sibul et al., 1999). Determination of the physiological state of the pest insect is therefore highly important. *Correspondence: Ivar Sibul, Faculty of Forestry, Estonian Agricultural University, Kreutzwaldi 5, EE51014 Tartu, Estonia. E-mail: isibul@eau.ee