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

Abstract

The respiration of the Cecropia silkworm was studied after the injn. of CN or in the presence of specific mixtures of O2, N, and CO. Positive pressure techniques were utilized to test the effects of CO/O2 ratios as high as 25:1. It was found that the respiration of the diapausing pupa is only slightly affected by high concns. of CO or CN. This minor effect was accounted for in terms of the CN- and CO-sensitivity of the contraction of the intersegmental muscles of the pupal abdomen. The other tissues in the dormant insect showed no detectable inhibi-tion by high concns. of CN or CO. Termination of the pupal diapause and progress of adult development are accompanied by a marked increase in the insect''s sensitivity to CN and CO. The effects of these agents are then no longer limited to muscular tissue but extend to the insect as a whole. CN or CO appear to act exclusively on the extra metabolism accompanying development and, thereby, to reduce the overall metabolism to the old diapausing level. The modes of action of CN and CO 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. It is concluded that cyto-chrome 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. 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.