Insects exchange respiratory gases with the external environment via a tracheal system which ramifies to provide direct delivery to all cells and tissues. The interface between the tracheal system and the outside world, the spiracles, requires stringent control to ensure adequate gas exchange while simultaneously preventing rapid loss of body water by evaporation from the large surface area of the tracheal system. Many insect taxa, both small and large, use a discontinuous external gas exchange cycle or DGC. The DGC has three distinct phases, closed spiracle (C), fluttering spiracle (F) and open spiracle (O). In many larger insects including beetles, gas movements during the O phase have a significant convective component. In some beetles, the F-phase appears to be convective with distinct microbursts of CO2 emission but the relative importance of diffusion and convection, particularly within the tracheal system is not clear. We investigated the relative importance of diffusion and convection in the DGC of C. verrucosa by exposing the beetle to mixtures of 21% O2 in inert balance gases with different diffusive properties during flow-through respirometry. Balance gases where nitrogen (normal diffusivity), helium (enhanced diffusivity) and sulfur hexafluoride (impeded diffusivity). We found that the O-phase in C. verrucosa is primarily convective as predicted whereas the F-phase has a strong diffusive component in addition to the convective component observed previously.
Species 1: Coleoptera Tenebrionidae Cryptoglossa verrucosa
Keywords: gas exchange, convection
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