Hormonal regulation of phase polymorphism and storage-protein fluctuation in the common cutworm, Spodoptera litura

Three storage proteins are synthesised by Spodoptera litura last-instar larvae as detected by an antiserum against pupal fat body proteins. The putative pupal storage proteins 1 and 2, appear in the haemolymph of the last-instar larvae 36 h after ecdysis under crowded rearing conditions: they appear 1 day later in isolated conditions. The appearance of these proteins in the haemolymph is prevented by juvenile hormone treatment and enhanced by allatectomy. Injection of 20-hydroxyecdysone into ligatured larvae does not induce appearance of these 2 proteins. Accumulation of protein 3 that reacts with Bombyx mori arylphorin antiserum is not blocked by juvenile hormone and is similar in both phases. It also accumulates to a small extent in the haemolymph during the moult to the final-larval instar and then disappears at ecdysis. One-hundred ng/ml ecdysteroid caused the sequestration of these proteins by the fat body, but a higher concentration of ecdysteroid (200 ng/ml) produced pupal cuticle in the isolated abdomens, suggesting that different ecdysteroid concentrations are necessary for these two events.