Ecdysteroid synthesis and molting by the tobacco hornworm, Manduca sexta, in the absence of prothoracic glands

Abstract

When a pair of prothoracic glands (PGs) were removed from Manduca sexta pupae on the day of pupation, the hemolymph ecdysteroid titer remained at a low level. When a portion of the gland pair was extirpated from pupae after the critical period for prothoracicotropic hormone release, the maximum hemolymph ecdysteroid titer was reduced in proportion to the mass of the PGs removed. These findings clearly showed that the PGs in intact pupae are responsible for the elevated ecdysteroid titer required to elicit adult development on schedule. When brains were removed on the day of pupation, the initiation of adult development was delayed for weeks or months. In contrast, pupae whose PGs were removed on the day of pupation initiated development only 7 days late, indicating the existence of an additional source of pupal ecdysteroids. Further, abdomens of male M. sexta that were isolated on the day of pupation initiated adult development spontaneously within 70 days. The implantation of day 0 pupal brains into these isolated abdomens accelerated the initiation of adult development and elicited synchronous adult development. The hemolymph ecdysteroid titer of those isolated abdomens receiving implants of brains increased within 5 days and reached a maximum level of 1.5 micrograms/ml. The analysis of hemolymph ecdysteroids by reverse-phase HPLC revealed that ecdysone was the major moiety and that the ecdysteroid composition was similar to that of normal, intact pupae that had just initiated adult development. These results demonstrate that the PGs are not requisite for adult development. An increased hemolymph ecdysteroid titer was also observed in isolated abdomens from which the testes were removed and in abdomens devoid of their digestive tract. Indeed, in the latter case, the ecdysteroid titer attained much higher levels than those observed for abdomens with intact guts. Despite numerous attempts to identify the tissue(s) in the isolated abdomens responsible for the increase in ecdysteroid titer, its identity remains unknown.

Neural regulation of sex-pheromone glands in Lepidoptera

“…Recent evidence supports the idea that some physiological processes in insects are controlled through multiple mechanisms (Hewes and Truman, 1991;Sakurai et al, 1991), and we believe that the mechanisms of pheromone biosynthesis and release are no exception (Christensen et al, 1992;Rafaeli and Gileadi, 1995). Normal activation of the pheromone gland may involve both neural and humoral mechanisms, or alternatively, the two regulatory mechanisms may be differentially activated at different times during the short lifespan of these insects or due to changing environmental conditions.…”

On the control of ecdysone biosynthesis by the central nervous system of blowfly larvae

“…Other larval and pupal tissues, so-called "secondary sources,'' were found to be able to secrete ecdysteroids [6,7]. Even cell lines of non-glandular origin were observed to produce ecdysteroids [8].…”

Expression of genes encoding proteins involved in ecdysteroidogenesis in the female mosquito, Aedes aegypti

“…In fourth instar larvae and pupae of A. aegypti, these same body regions were found to be the de novo source, both in vitro and in vivo, of circulating ecdysteroids (Jenkins et al, 1992), whereas the prothoracic glands of larvae failed to produce ecdysteroids in vitro. In a variety of insect species and developmental stages, tissues other than prothoracic glands and gonads are known to produce ecdysteroids (Delbecque et al, 1990;Sakurai et al, 1991).…”