Entomology

Respiration of small insects

In the life sciences there is considerable interest in the detection of minute quantities of trace gasses like CO₂ released by various biological sources. Trace gas detectors based on infrared (laser) spectroscopy are a good option for this, especially when fast, on-line time resolution is needed. Up to now, the technique has been limited by the availability of suitable laser sources for the wavelength range with the strongest absorptions of gasses. For CO₂ this is near 4.234 µm in the infrared wavelength region. Here, we present a new optical parametric oscillator generating high-power, continuously tuneable laser radiation (between 3.9 and 4.8 µm) in continuous-wave, single mode operation. As a CO₂ detector, this system is able to detect concentrations as low as 0.7 parts per billion. This was demonstrated by monitoring the respiration of a 3.7 mg ant (Lasius niger).

Methane emission by cockroaches

Biogenic sources are responsible for the major part of the worldwide methane (CH₄) flux (> 70%). Termites and other arthropods such as millipedes, cockroaches and scarab beetles are found to produce CH₄ and it is believed to contribute as much as 25% of the total production. The fact that atmospheric CH₄ contributes significantly to the process of global warming and ozone depletion justifies research in this field. In the past measurements employing gas chromatography have been performed, allowing measurements of the CH₄ release of a single animal only after incubation for several hours.

The CO-laser based detector revealed the dynamic character of the gas emission; it yields fast response times and permit observation of the dynamics of the emission of CH₄, CO₂ and water vapor.

Cockroaches at rest show a regular breathing pattern that is postulated to reduce water loss and optimize O₂ uptake. This breathing is accomplished by a complicated sequence of opening and closing of the spiracle valves of the tracheal system and by venting the content of the tracheae through abdominal motions. As shown in the graph the H₂O, CO₂ and CH₄ emission are monitored during the complete sequence of fluttering, ventilation and constriction for different insects.