Intratracheal Pressure in Insect Respiration

Most adult insects maintain a direct gaseous exchange between the environment and tissues by means of a tracheal respiratory system. Packard (1898), Vinal (1919), Snodgrass (1925, 1935) and Wigglesworth (1939) have extensively investigated and described the morphology of the insect respiratory system. Du Buisson (1924), Lee (1925, 1927), McKay (1927), Uvarov (1928), McArthur (1929), McGovran (1931) and Kitchel and Hoskins (1935) have investigated the coordination of abdominal movement, opening and closing of spiracles and the passage of air through the tracheal systems of several orthoptera. These investigations established the concept that there is a directed tracheal ventilation in insects. Inspiration occurs through an anterior group of spiracles. The air is then passed through the tracheal system and expired through a posterior group of spiracles. However some of these workers found that occasionally any of the spiracles might serve for both inspiration and expiration and that when the grasshopper was struggling or respiration was stimulated by carbon dioxide the normal direction of tracheal ventilation might be reversed. In all cases it was thought that the respiratory cycle consisted only of inspiration and expiration which ventilated the larger trachea and air sacs. Oxygen was then carried through the smaller trachea and air sacs by diffusion to the site of absorption at the end of the tracheoles. The tracheal system was considered to be open to the air at all times and in no case was the intratracheal pressure believed to be greater than ambient pressure.