Intratesticular ecdysteroid titres and the arrest of sperm production during pupal diapause in the tobacco hornworm, Manduca sexta

Abstract

Lepidopteran spermatogenesis, which is a dichotomous process producing concomitantly both eupyrene (nucleate) and apyrene (anucleate) spermatozoa, discontinues during diapause. In diapause-averting pupae of Manduca sexta, the intratesticular titre of 20-hydroxyecdysone increases sharply to a post-pupation peak in day-10 pupae, and then drops sharply. In contrast, the titre is persistently low throughout diapause. In diapause-averting pupae, the post-pupation ecdysteroid peak and its abrupt decline, occur shortly before cessation of eupyrene meiosis. Accordingly, eupyrene meiosis continues uninterruptedly in diapausing larvae having experienced neither the peak, nor the fall of the ecdysteroid titre. The advance of apyrene spermatocytes towards meiotic metaphases coincides in diapause-averting pupae with the post-pupation rise in ecdysteroid titre. Accordingly, in diapausing pupae lacking this rise, apyrene spermatocytes stop developing, and lyse, before entering metaphase. The lack of the post-pupation peak of ecdysteroid may be related also to the lysis of eupyrene spermatids in the diapausing larvae. Fluctuations of the intratesticular ecdysteroid content follow the corresponding patterns of fluctuations in haemolymph ecdysteroid content in both diapausing and diapause-averting pupae. These findings do not support the idea that testicular ecdysteroids may play a separate, major role on controlling discontinuity of sperm production during diapause in Manduca.