The stage-dependent effects of
starvation on the growth, metamorphosis, and ecdysteroidogenesis of the prothoracic glands during the last larval instar of the silkworm, Bombyx mori, were studied in the present study. When last instar larvae were starved beginning on day 1 of that instar, all larvae died between days 5 and 7 of the instar. Although the
prothoracicotropic hormone (PTTH) release from the brain-corpus cardiacum-corpus allatum (BR-CC-CA) did not significantly change during
starvation, a deficiency in PTTH signal transduction was maintained, which led to very low levels of hemolymph
ecdysteroids after the beginning of
starvation. However, when
starvation began on day 3 of the last larval instar, the major hemolymph
ecdysteroid peak, preceding larval-pupal transformation, occurred 1 day earlier than that in control larvae.
Protein content of the prothoracic glands in day 3-starved larvae was maintained at a low level as compared to that of control larvae. The secretory activity of the prothoracic glands in day 3-starved larvae was maintained at a level similar to that of control larvae. However, the rate of ecdysteroidogenesis, expressed per microgram of glandular
protein, was greatly enhanced in these starved larvae, indicating that upon
starvation, larvae increased the
ecdysteroid production rate to enhance the rate of survival.