CORRELATIONS BETWEEN ECDYSTEROID TITER AND SILK GENE-EXPRESSION IN THE LAST INSTAR LARVAE OF GALLERIA-MELLONELLA (LEPIDOPTERA, PYRALIDAE)

Developmental profiles of total RNA and four silk protein mRNAs exhibi t different correlations with ecdysteroid titre changes in course of t he 180 hr-long last larval instar. Total RNA and heavy-chain fibroin m RNA increase gradually until 168 hr and 156 hr, respectively, dropping sharply afterwards. The content of sericin1 mRNA rises for 120 hr, re mains high until 168 hr and then drops. The amounts of ligh-chain fibr oin mRNA and sericin2 mRNA increase sharply at the start of the instar ; the former rises until 168 hr, whereas the latter begins to decline already at 120 hr. The pupation-inducing ecdysteroid surge at 144-168 hr causes a drop in all examined RNA classes. Similar drop is induced precociously with exogenous ecdysterone, while a slow decrease of RNA contents to similar bottom levels occurs when the larvae are ligated b ehind prothorax.