PHYSIOLOGY OF INSECT DIAPAUSE. X. AN ENDOCRINE MECHANISM FOR THE INFLUENCE OF TEMPERATURE ON THE DIAPAUSING PUPA OF THE CECROPIA SILKWORM

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Abstract
The termination of the pupal diapause of the Cecropia silkworm is potentiated by preliminary exposure to low temperature and, especially, to temperatures in the range 6-15[degree]C. This effect is mediated by an endocrine mechanism which centers in the brain, and is specifically concerned with restoring the competency of the brain''s neurosecretory cells to synthesize and secrete the brain hormone. The time required for the initiation of adult development at 25[degree]C is thereby reduced from 27 weeks to as little as one day. As soon as the brain has recovered its endocrine function, the catalytic effects of low temperature are at an end; the actual secretion of the hormone and the developmental response that follows are then favored by high temperature. In this manner the low temperatures of winter potentiate the initiation of adult development the following spring. Effects of low temperature on the inactive, diapausing brain are considered in detail. The action is apparently a direct one on temperature-sensitive reactions within the brain itself. The over-all process of activation shows the kinetics of a threshold reaction but not of an all-or-none reaction. These findings are discussed in the light of Van der Root''s chemical and physiological studies of the brain of Cecropia. Within the substance of the brain the primary change induced by low temperature appears to be the synthesis and accumulation of a cholinergic substrate.