Ecdysones and imaginal disc development during the last larval instar of Pieris brassicae.
ABSTRACT Ecdysone haemolymph levels and in vivo development of imaginal wing discs have been studied during the last larval instar of Pieris brassicae.During this period, β-ecdysone variations show two successive peaks, the first one related to the induction of wandering stage, and the second (main) one to pupal cuticle synthesis. The observed situation is very similar to that of Manduca sexta. Imaginal wing disc growth is composed of several genetically programmed steps that need the presence of ecdysone, but do not appear very closely linked to circulating hormone levels. It seems that ecdysone haemolymph peaks should be considered as periods where ecdysone levels are above a threshold value.
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ABSTRACT: Changes in prothoracic gland morphology were correlated to developmental events and ecdysteroid titres (20-hydroxyecdysone equivalents) during the last-larval instar in Spodoptera littoralis. After ecdysis to the last-larval instar the haemolymph ecdysteroid titre remained at about 45 ng/ml, when the prothoracic glands appeared quiescent. The first signs of distinct gland activity, indicated by increased cell size and radial channel formation, were observed at about 12 h prior to the cessation of feeding (36 h after the last-larval moult), accompanied by a gradual increase in ecdysteroid titre to 110 ng/ml haemolymph, at the onset of metamorphosis. During this phase ecdysteroid titres remained at a constant level (140–210 ng/ml haemolymph) and prothoracic gland cellular activity was absent for a short period. The construction of pupation cells occurred when haemolymph ecdysteroids titres increased to 700 ng/ml. A rapid increase in ecdysteroids began on the fourth night (1600 ng/ml haemolymph) reaching a maximal level (4000 ng/ml haemolymph) at the beginning of the fourth day. In freshly moulted pupae a relatively high ecdysteroid titre (1100 ng/ml haemolymph) was still observed, although during a decrease to almost negligible levels. The increase in ecdysteroid level during the third and the fourth nights of the last-larval instar was correlated with the period when almost all the prothoracic gland cells showed signs of high activity. Neck-ligation experiments indicated the necessity of head factors for normal metamorphosis up to the second to third day of the instar. The possibility that the prothoracic glands are under prothoracicotropic hormone regulation at these times is discussed.Journal of Insect Physiology 01/1985; DOI:10.1016/0022-1910(85)90010-1 · 2.50 Impact Factor
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ABSTRACT: In last instar larvae of Galleria mellonella, the observed increase in the number of cells of growing intact imaginal wing disks was completely blocked by ligation of the mesothorax and stimulated again by external applications of low and high doses (2.6 to 130 μg/g) of ecdysterone. However, at no hormonal dose applied has the full extent of normal wing growth been attained. The ecdysteroid dependent cuticle synthesis could be induced in disks of various sizes. The cell number of imaginal disks of young last or supernumerary instar larvae is exponentially correlated with the body weight. The rates of cell division during prepupal development of the wing disk appeared to be about the same in last and supernumerary instar larvae.In normal pupae the borders of the everted wings are fitted precisely to a cuticular demarcation line on the underlying abdomen. X-ray irradiations of last instar larvae led to a reduction of the pupal wing surface and cell number, but did not affect the position of the demarcation line. The X-ray experiments confirm the finding that reduced wings are capable of normal pupal cuticle synthesis.Journal of Experimental Zoology 08/1980; 213(2):185 - 197. DOI:10.1002/jez.1402130205
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ABSTRACT: The variations in circulating ecdysteroids and juvenile hormones (JH) in Galleria, from the end of the antepenultimate larval stage until emergence of adults, have been determined. The two hormonal families were extracted separately from the same hemolymph sample and quantified by two radioimmunoassays. Juvenile hormone RIA activity was about 35 nM in larvae of the antepenultimate and penultimate stages. It dropped before each molt and increased thereafter. Moreover, it gradually decreased during the last larval instar. In pupae, it was generally low, but it rose drastically during the late pupal development and in young adults. This rise was very much higher in females than in males. Three different RIA-active compounds were found; they were assumed to be JH-I, JH-II, and JH-III according to their retention times in HPLC. The three compounds were present in almost equal concentration in larvae of the penultimate stage: JH-I predominated, however, during the last larval instar. In late pupae, the main hormone was JH-III both in males and in females. There is no clear relationship between ecdysteroid and juvenile hormone changes, except for a female-specific ecdysteroid rise which coincides with the juvenile hormone release in late pupae. This double hormonal stimulation can be involved in the regulation of vitellogenin synthesis and deposition in oocytes.General and Comparative Endocrinology 12/1984; 56(2):218-30. DOI:10.1016/0016-6480(84)90034-0 · 2.67 Impact Factor