Spermidine supplementation accelerates time of pupariation and contributes to early degeneration of silk glands in Bombyx mori (Lepidoptera: Bombycidae)

Spermidine is a ubiquitous biogenic amine that is known to promote growth, development and autophagy. The silk glands of Bombyx mori L. (Lepidoptera: Bombycidae) produce mulberry silk, which has high economic value. Silk is released during the formation of a cocoon, and the glands undergo degradation involving both autophagy and apoptosis. The present study explores the effect of spermidine feeding on the maturation of B. mori 5th instar larvae with particular emphasis on its role in growth at the end of the larval stage and during the early phase of the silk gland degeneration. 5th instar larvae were divided into two groups and fed with control and spermidine-treated mulberry leaves. At the end of the 5th instar stage, the spermidine group showed a significant increase in body and silk gland weights, which helped in achieving larval critical weight prior to the control group. Significantly elevated levels of Atg8 expression, an increased number of lysosomes and high chromatin condensation were observed in the Spd group during the early larval - pupal transition phase, which helped in prior silk gland degeneration.