THE PHYSIOLOGY OF INSECT DIAPAUSE. VIII. QUALITATIVE CHANGES IN THE METABOLISM OF THE CECROPIA SILKWORM DURING DIAPAUSE AND DEVELOPMENT

¹ The Biological Laboratories, Harvard University, Cambridge 38, Massachusetts

1. The respiration of the Cecropia silkworm was studied after the injection of cyanide or in the presence of specific mixtures of oxygen, nitrogen, and carbon monoxide. Positive pressure techniques were utilized to test the effects of carbon monoxide/oxygen ratios as high as 25:1.

2. It was found that the respiration of the diapausing pupa is only slightly affected by high concentrations of carbon monoxide or cyanide. This minor effect was accounted for in terms of the cyanide- and carbon monoxide-sensitivity of the contraction of the intersegmental muscles of the pupal abdomen. The other tissues in the dormant insect showed no detectable inhibition by high concentrations of cyanide or carbon monoxide.

3. The termination of the pupal diapause and the progress of adult development are accompanied by a marked increase in the insect's sensitivity to cyanide and carbon monoxide. The effects of these agents are then no longer limited to muscular tissue but extend to the insect as a whole. Cyanide or carbon monoxide appear to act exclusively on the extra metabolism accompanying development and, thereby, to reduce the overall metabolism to the old diapausing level.

4. The modes of action of cyanide and carbon monoxide within the diapausing and non-diapausing insects are considered in detail. Insensitivity to these agents, as in most tissues of the diapausing pupa, argues in favor of the presence and utilization of a terminal oxidase other than cytochrome oxidase.

5. It is concluded that cytochrome oxidase is the principal terminal oxidase of only the somatic musculature of the diapausing pupa. Months later, with the termination of the pupal diapause, cytochrome oxidase becomes the principal terminal oxidase of the growing, post-diapausing insect as a whole.

6. These qualitative changes in the insect's metabolism are synchronized with the secretion of the hormone responsible for the termination of diapause and the development which follows, and appear to be a more or less immediate result of the hormonal action.