Midgut of Lepidopteran pupae is a major depot of sequestered, mobilizable, ecdysteroids

Abstract

Extirpation of endocrine organs - a classic maneuver in hormonal research - has been difficult or impossible in the case of the prothoracic glands (PG) of insects. In larval and pupal Lepidoptera the glands are virtually inaccessible unless one sacrifices the insect. Even then, the PG are not easy to remove in their entirety. Consequently, in order to obtain viable preparations lacking PG, one costomarily makes use of abdomens isolated by litigation or surgery

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

“…Our data reveal that isolated abdomens of Manduca can initiate and complete adult development spontaneously in the absence of brain and prothoracic gland. Williams [12] suggested that the gut may be the reservoir for ecdysteroids in the abdomen but our results demonstrate that isolated abdomens lacking a gut also initiated adult development. The lepidopteran testis does produce ecdysone and this production is stimulated by brain extracts [16], but testis removal did not affect the adult development of Manduca isolated abdomens.…”

“…10C). The titer then declined to about 1.8 pg/ml by day 12 and remained at about that level for the remainder of the period analyzed.…”

“…4.3 days after isolation (n = 12). The gut and/or gut contents have been postulated as possible reservoirs of ecdysteroids that influence pupal-adult development [12] and, therefore, a series of isolated abdomens lacking digestive systems were prepared, examined, and analyzed. Of 57 such preparations, 22 isolated abdomens (39%) initiated adult development and formed complete external adult characteristics including pigmented scales and genitalia, although they did not eclose.…”

“…The difference between the latter study and those of Williams is that in the preparation of the isolated abdomen Sehnal and his colleagues left the gut in place whereas Williams removed the gut. This led Williams [12] to propose that the gut is a major depot of sequestered ecdysteroids, in contrast to studies on Manduca sexta indicating that the guts of newly eclosed pupae contain only small amounts of free and conjugated ecdysteroids [13].…”

Role of juvenile hormone in the hypermetabolic production of water revealed by the O₂ consumption and thermovision images of larvae of insects fed a diet of dry food

“…The original, brain-PG theory of Williams (1952) claimed that the PG is the direct target of the brain hormone and its primary hormonal function is to regulate moults and ecdyses. The theory was considerably elaborated and widely disseminated by Gilbert & Schneiderman (1961) and has persisted as the main hormonal concept in insect developoment (Riddiford, 1996), although it was refuted a long time ago (Williams, 1987) by its creator. We found (Sláma, 1983(Sláma, , 1988(Sláma, , 1998) that the brain-PG model does not correspond with reality.…”