The Respiration of Insects

Abstract

Summary The review covers the ground of external and internal respiration in insects, but deals neither with quantitative changes in metabolism, nor with the intimate processes of oxidation in the tissues. The general anatomy and histology of the tracheal system are described. The form of the tracheae and their mode of ending in the tissues is extremely varied in different insects and in different organs. The question whether the tracheal endings contain fluid or air and the problem of what forces keep the larger branches filled with gas are discussed in detail. The embryological development of the tracheal system and the nature of the “spiral thread” are briefly considered. The exchange of gases in the tracheal system is effected primarily by diffusion. This is modified by opening and closure of the spiracles (“ diffusion control ”) and by mechanical ventilation of the larger tracheal branches (“ventilation control ”). The mechanism of tracheal ventilation is discussed at length: including the part played by the air sacs and the question whether there is a directed stream of air through the tracheal system. The respiratory movements are controlled by nerve centres, variously situated in different insects; and these centres may be stimulated either by oxygen want or by carbon dioxide excess. The relative importance of the spiracles and the skin in respiration, especially in the elimination of carbon dioxide, is discussed. Under the respiration of aquatic insects the functions of the “blood gills,”“tracheal gills ” and “ cuticular gills ” are reviewed, and the problems connected with the “ hydrofuge ” structures of aquatic insects and the air stores which they carry are considered. The respiration of parasitic insects presents many parallels with that of aquatic forms. The part played by the blood of insects as a carrier of oxygen is discussed in detail.

Control of body size by oxygen supply reveals size-dependent and size-independent mechanisms of molting and metamorphosis

“…reducing the length of the path over which oxygen needs to diffuse to reach internal tissues (33,34). It has been suggested that the evolution of gigantic insects in the Paleozoic was associated with a high level of atmospheric oxygen (13,17,18).…”

Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle

“…In fact as far back as 1931, Wigglesworth noted that it was generally accepted that respiratory movements such as abdominal and thoracic pumping function to alternately compress and dilate the tracheal system (Wigglesworth, 1931). However, the mechanical problem with this idea is that taenidal rings, which are thickenings in the tracheal wall, can be viewed as morphological specializations that prevent rather than promote collapse.…”

“…Second, aside from a few basal groups, most insects are understood to have continuous, non-compartmentalized tracheal systems (e.g. Hetz, 2007;Wigglesworth, 1931), and our highresolution x-ray images have not revealed any evidence of valving or compartmentation in the tracheal system of Pterostichus stygicus. Direct confirmation that tracheal compression drives air through the spiracles will require measurement of airflow through the spiracles, or the contributions of convection and diffusion could be quantified by manipulating the density of the air in the flow-through system by replacing N 2 with SF 6 or helium.…”

Respiratory function of the plastron in the aquatic bug,Aphelocheirus aestivalis(Hemiptera, Aphelocheiridae)

“…Insects rely primarily on their tracheal system to exchange respiratory gases with the atmosphere (Wigglesworth, 1931). The system consists of air-filled tubes that open to the air through spiracles on the surface of the thorax and abdomen, branch throughout the body, and eventually reach the cells with blindended tracheoles.…”