Morphoanatomic evolution and ecdysteroid variation during the metamorphosis of Neodiprion sertifer

Previous studies have emphasized that, in sawfly metamorphosis, most of morphogenesis and hormonal activity occurs during the pronymphal phase in the prepupal stage. The titres of ecdysteroids in haemolymph and ovaries were measured in selected stages of development of the sawfly Neodiprion sertifer (Hymenoptera Diprionidae), during the metamorphosis and in the adult. The hormonal levels detected were compared with the main morphological and anatomical differentiations observed. The last larval instar showed a peak of ecdysteroid secretion about two days before the apolysis. During the prepupal stage there were two peaks of ecdysteroid secretion with the second much higher. At the pupal stage a sudden increase of the hormone titre was found. The sawfly therefore showed a variation of the molting hormone titre comparable with that observed for other holometabolous insects. Moreover an intense secretive activity of the ovaries from the late pupal stage to the adult stage was clearly detected. The dose-response hypothesis of ecdysteroid action is discussed.