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Journal of Experimental Biology 32,681-691 (1955)
Published by Company of Biologists 1955

Further Studies of Gas-Filling in the Insect Tracheal System

JOHN BUCK ¹ and MARGARET KEISTER ¹

¹ National Institutes of Health Bethesda 14, Maryland, U.S.A.

1. In Sciara larvae exposed to total anoxia before moulting, all visible movement and all visible change in the content of the tracheal system cease. Moulting and tracheal gas-filling can be postponed at least 1 hr. beyond normal time.

2. In most third-stage larvae exposed to 0.3-0.75% O₂ before the third moult, the future fourth-stage tracheal system, which is present fully-formed in the body, fills with gas .This shows that although moulting invariably precedes gas-filling under normal circumstances it need not do so.

3. In premoult larvae which have filled their trachea with gas upon exposure to 0.3-0.75% O₂, the tracheae fill again with liquid when the larvae are put back into atmospheric air. This reversal of gas-filling can be alternated with gas-filling several times in the same individual.

4. The fact that in reversal of gas-filling an increase in pO₂ promotes liquid-filling, whereas in moulted larvae it not only never leads to liquid-filling but actually accelerates gas-filling, indicates that some basic, but at least temporarily reversible physiological or chemical change occurs in the tracheae or in the metabolism of the peritracheal tissue, near the time of moulting. A partial explanation of the observed phenomena can be made in terms of a combination of active uptake and physical uptake of tracheal liquid. Evidence for the existence of both types of mechanism, separately, has been adduced by Wigglesworth in other material.