Activity of the Brain /

Pupal diapause in Mimas tiliae can be terminated by keeping the pupa for at least 4 weeks at 3° C. The adult emerges about 15 days after transfer to 25° C. Histological examination shows that the neurosecretory cells in the brain are inactive in the diapausing pupa, but they elaborate intracellular material during the first 3 weeks at 3 C. The material is passed to the corpora cardiaca. The neurosecretory cells are again inactive by the end of the low-temperature period. The brain/cardiaca system shows little sign of secretory activity during the subsequent period at 25 ° C. The corpora cardiaca undergo phagocytosis and reorganization during this time. This suggests that conditions for further development are established by the end of the low-temperature period. This hypothesis is supported by the fact that development of the non-endocrine organs begins immediately the pupa is transferred to 25° C after 4 weeks at 3 C. Extirpation and implantation experiments involving the brain, with and without its associated corpora cardiaca, support the histological results, indicating that the brain is necessary for diapause development at 3° C and that the corpora cardiaca are involved in the release of the brain factor.