Reduction in the critical number of short days for pupal diapause in Papilio machaon with precocious metamorphosis

Normal and allatectomized larvae of Papilio machaon were transferred from short (light:dark 10:14) to long (light:dark 16:8), or long to short days, on successive days of larval development to examine the critical number of short days necessary for diapause induction. The reciprocal transfer revealed that the normal larvae required 12 consecutive short days during the early instars to raise the incidence of pupal diapause to 50%. The critical number of short days was reduced to 9.5 days when the length of the larval period was cut due to precocious pupation induced by allatectomy. The reduction in the critical number of short days with precocious metamorphosis was less remarkable when the larvae were exposed to short days during the late instars. A possible summation mechanism of photoperiodic information for diapause induction in P. machaon is presented to explain the results obtained.