Following the theoretical analysis by Krogh, and subsequent confirmation thereof by Weis-Fogh (review in Miller 1974), which showed that diffusion could serve the gas exchange requirements of small insects and most large insects at rest, diffusion has regularly been assumed to be the only means by which insects exchange gases at rest. Indeed, this idea continues to permeate modern discussions (West et al. 1997), despite the fact that ventilation, either by abdominal pumping or by movements of other sclerites, has been suspected since 1645, and has been confirmed by observation and using modern experimental methods at least since the 1960s (Schneiderman and Williams 1955; Miller 1981). Even ventilation by means of tracheal expansion and contraction, which was recently hailed as a major new discovery (Westneat et al. 2003) has been known since the 1930s (Herford 1938). Gas exchange patterns and mechanisms in insects have been reviewed several times (Miller 1974, 1981; Kaars 1981; Wasserthal 1996), and the importance of both diffusion and convection (by ventilation in many cases) for gas exchange at rest is now well established.
Within a particular species, metabolic rates at rest vary over the course of development (Clarke 1957), during diapause (Denlinger et al. 1972), over the course of a day (Crozier 1979; Takahashi-Del-Bianco et al. 1992), between seasons (Davis et al. 2000), and as a consequence of changing temperature, water availability, and size. The latter variation is most interesting from an ecological perspective, and has consequently been the source of most controversy.
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