Study of gas exchange in insects by sensitive laser photoacoustic spectroscopy

Although quantifying gas exchange in small insect species is of great biological interest, the progress in this field of research is hampered by the inability of most gas detectors to monitor the low emission rates from these insects. Recently, laser based photoacoustic spectroscopy (LPAS) has emerged as a highly sensitive technique that allows gases to be detected at sub-ppb level. In this work, LPAS was used to study gas exchange in two different insect species. Firstly, loss of water by the minute Western Flower thrips (Frankliniella occidentalis , average weight 50 mu g) was recorded by means of CO-laser PAS. Water loss by a single thrips could be on-line recorded with a practical detection limit of 30 ppb. Insects released H2O in rather regular patterns, possibly due to discontinuous respiration. These data represent on-line H2O loss recordings of the smallest insects measured hitherto. In a second experiment, the inert tracer gas SF6 was used to determine the tracheal volume of Attacus atlas pupae. Insects were loaded with SF6 and subsequent release of this gas was monitored using CO2-laser PAS. Based on the amount of released SF6 , one has determined the tracheal volume of Attacus atlas pupae. The value obtained (170 +/- 53 mu L/g) is in good correspondence with data obtained by other techniques. In addition, with this technique, respiration patterns can be recorded; the results show a good correspondence with the simultaneous recordings of CO2 release using a commercial CO2 analyser