Ecdysteroid titres and location in developing eggs of Schistocerca gregaria

Ecdysteroid levels in the separated embryo and yolk fractions of Schistocerca gregaria eggs have been determined at each of the developmental stages. The major hormones present both in the free and conjugated state are ecdysone, 20-hydroxyecdysone and 2-deoxyecdysone. At the beginning of embryonic development the ecdysteroids occur only in the yolk whereas, after blastokinesis, they are found in the embryo. The levels of conjugates fall during embryonic development, whereas a decrease of free hormone titres in early embryogenesis is followed by a marked increase in late embryos (stage 26 and 28). The possible role of ecdysteroids in relation to the morphogenetic processes of egg development and the site of origin of the free ecdysteroid peaks are discussed.     

Effects of juvenile hormone analogs and 20-hydroxyecdysone on diapause termination in eggs of Locusta migratoria and Oxya yezoensis

To understand the hormonal control of embryonic diapause, juvenile hormone analogs (JHAs), methoprene and hydroprene, and 20-hydroxyecdysone (20E) were applied onto diapause eggs of Locusta migratoria and Oxya yezoensis. These insects enter diapause at the mid-stage of embryogenesis prior to blastokinesis. Topical application of JHAs significantly facilitated diapause termination in both species but JHA-treated embryos underwent abnormal morphogenesis, pigmentation and sclerotization without dorsal closure. The Locusta eggs immersed in the 20E solution for 24h terminated diapause in a dose-dependent manner. We also investigated phosphorylation of extracellular signal-regulated kinase (ERK), a member of mitogen-activated protein kinase (MAPK), during diapause-terminating process of Locusta migratoria and found that ERK was activated either by cold exposure or JHA treatment. The possible involvement of the hormones and ERK in embryonic diapause and the possibility of ecdysteroids synthesis by prothoracic glands of diapause embryo were proposed.     

Ecdysteroid and juvenile hormone changes in Bombyx mori eggs, related to the initiation of diapause

We describe a method for the routine determination of changes in juvenile hormone levels in insect eggs. The hormones are first converted into their diol derivatives, then they are purified from other lipids and separated by high-performance liquid chromatography (HPLC). The radioimmunoassay of the fractions was then determined. The method permits the simultaneous assay of ecdysteroids, and it was used for determining the hormonal changes in Bombyx eggs during the pre-diapause development. Our major finding is that the hormonal content of eggs dramatically increased prior to the initiation of diapause. This hormonal rise included ecdysone, 20-OH-ecdysone and 3 juvenile hormones. The HPLC retention time of the latter corresponded to JH₁ JH₂ and JH₃. Subsequently, the embryos entered diapause and the hormonal content of eggs was reduced to traces of ecdysteroids. These dramatic changes in juvenile hormone levels during early embryogenesis raise a number of issues which are developed in the discussion.     

Endocrine interrelationship between the parasitoid Chelonus sp. and its host Trichoplusia ni

The egg-larval parasitoid Chelonus sp. induces the precocious onset of metamorphosis in the 4th (penultimate) stadium of its host Trichoplusia ni, emerges from the prepupa, and then feeds on it. Qualitative and quantitative changes in ecdysteroids and juvenile hormone were measured. Hemolymph of 3rd-to 4th-instar host larvae and the parasitoids they contained, as well as nonparasitized and parasitized eggs, were analyzed. In the host hemolymph a broad peak of ecdysteroids during molting into the 4th stadium and a continuous increase from day 2 (onset of precocious wandering) until day 4 (emergence of parasitoid) were observed; 20-hydroxyecdysone and 20,26-dihydroxyecdysone were predominant. The juvenile hormone titer fluctuated in the 3rd and early 4th stadium and fell to undetectable levels shortly before the precocious onset of wandering. The parasitoid's ecdysteroids started to increase on the molt to the 2nd instar (= early 4th instar of the host) and thereafter fluctuated on a high level, 20-hydroxyecdysone, 20,26-dihydroxy-ecdysone, and ecdysone being predominant. The juvenile hormone titer was high in late 1st-instar parasitoids, decreased to low levels at ecdysis into the 2nd instar, and increased again to high levels in the 2nd-instar larvae at the time when their shape changed from flat to cylindrical. After ecdysis to the 3rd instar the juvenile hormone titer fell. A comparison revealed that both ecdysteroids and juvenile hormone fluctuate independently in parasitoid and host at most stages, suggesting that the parasitoid produces its own hormones. The first data on ecdysteroids and juvenile hormones in the egg stage of a parasitoid/host system are reported. At the stage of eye pigmentation parasitized eggs contained more immunoreactive midpolar ecdysteroids than non-parasitized ones. 20-Hydroxyecdysone and 20,26-dihydroxyecdysone were the predominant ecdysteroids in both nonparasitized and parasitized eggs, but the latter contained several additional ecdysteroids which were not seen in nonparasitized eggs. The titer of juvenile hormone was similar in both. Shortly before hatching the ecdysteroids were low in parasitized and nonparasitized eggs, but the content of juvenile hormone was much higher in the former. At this stage the majority of parasitoids have already eclosed and teratocytes are released. The results of HPLC analysis indicated the presence of juvenile hormone III together with juvenile hormones I and II in parasitized eggs, but only juvenile hormones I and II in nonparasitized eggs.     

Qualitative and quantitative analyses of juvenile hormone and ecdysteroids from the egg to the pupal molt in Trichoplusia ni

A method was developed to determine in the same extract juvenile hormone and various types of ecdysteroids in precisely staged eggs and larvae of Trichoplusia ni. Ecdysteroids were tentatively identified on the basis of their retention time in ion suppression reversed-phase HPLC and their cross-reactivity with two relatively non-specific, complimentary antibodies, whereas juvenile hormone was identified using reversed-phase HPLC combined with Galleria bioassay. Freshly laid eggs contained low levels of immunoreactive ecdysteroids. Mid-polar ecdysteroids increased in the phase of segmentation (14-18 h) and 1st larval cuticle formation (36-44 h), when 20-hydroxyecdysone and 20,26-dihydroxyecdysone were found to be predominant. Only traces of ecdysone and 26-hydroxyecdysone were seen. Toward hatching ecdysteroids decreased and represented mainly compounds more polar than 20,26-dihydroxyecdysone. In larval development ecdysteroids were low at the beginning of the feeding phases, increased toward cessation of feeding, and reached highest levels 12-15 h before ecdysis. In feeding stages ecdysone and 20-hydroxyecdysone were predominant, whereas in molting stages they were seen together with 20,26-dihydroxyecdysone and 20-hydroxyecdysonoic acid. The juvenile hormone titer was very low in freshly laid eggs and was high (approximately 25 ng/g) in embryos at the stage of 1st larval cuticle formation and eye pigmentation. In eggs we tentatively identified juvenile hormones I and II, whereas in larval stages juvenile hormone II appeared to be the predominant or exclusive juvenile hormone. Its titer fluctuated rapidly and was high in early 1st-instar larvae and again before the molts into the 3rd, 4th, and 5th instar. Highest titers were reached concomitant with the peak in 20-hydroxyecdysone 12-15 h before ecdysis.     

Changes in ecdysteroids during embryogenesis of the blue crab, Callinectes sapidus rathbun.

Total ecdysteroid titers [estimated by radioimmunoassay (RIA)] in embryos of the blue crab increased from ～6 ng 20-hydroxyecdysone equivalents/g in the immature embryo to a maximum of ～500 ng 20-hydroxyecdysone equivalents/g in maturing embryos; titers dropped to ～300 ng 20-hydroxyecdysone equivalents/g in prehatch embryos. High-pressure reverse-phase chromatography of the embryo extracts resolved five RIA-active components. α-Ecdysone and the polar conjugate of 20-hydroxyecdysone were present in low quantities. The concentration of 20-hydroxyecdysone increased during embryogenesis to a maximum of ～160 ng/g in maturing embryos and decreased only slightly in the prehatch embryos. Two unidentified components were also detected and the changes in their concentrations were estimated. One, an apolar component (peak III), accounted for as much as 63% of the total RIA activity as the embryos matured. The estimated concentration of this component increased from 85 ng/g in early embryos to 475 ng/g in maturing embryos, then decreased by 50% in the prehatch embryos. The level of the other, more polar component (peak II) increased from 7.5 to 75 ng/g as the embryos developed. The increase in the concentration of ecdysteroids during embryogenesis indicates that crab embryos have the capacity to synthesize ecdysteroids and suggests that these hormones may have a physiological role in the embryonic development of crustaceans.     

Prothoracicotropic hormone activity in the embryonic brain of the tobacco hornworm,Manduca sexta

Summary Head segments and brains were extirpated from embryos of the tobacco hornworm,Manduca sexta, extracted and the resulting extracts assayed for prothoracicotropic hormone (PTTH) activity on prothoracic glands from day 3 fifth instar larvae and day 0 pupae. Dose-response curves were generated and indicated the presence of PTTH activity in embryonic brains and head segments, suggesting a role(s) for this neurohormone during embryogenesis. Maximal PTTH activity was found in brains from embryos 117 h post-oviposition, just prior to hatching, but activity was also noted in head segments as early as 24 h postoviposition. These data on PTTH and those on ecdysteroids and juvenile hormones in embryos suggest that these 3 classes of hormones which control insect post-embryonic development, may also be involved in the regulation of developmental processes in the embryo.     

Profile of free and conjugated ecdysteroids and ecdysteroid acids during embryonic development of Manduca sexta (L.) following maternal incorporation of [14C]cholesterol

The levels of both free and conjugated ecdysteroids, maternally labeled from [¹⁴C]cholesterol, of six different age groups of Manduca sexta eggs were quantitatively determined. Eggs 0–1-h old contain about 2.5 and 35 μ/g of the 2- and 26-phosphates of 26-hydroxyecdysone, respectively, and 1 μg/g of 26-hydroxyecdysone. During embryogenesis of 26-hydroxyedcdysone 26-phosphate is hydrolyzed to 26-hydroxyecdysone, which reaches a peak titer in 1–18-h-old eggs; the level of 26-hydroxyecdysone 2-phosphate remains rather constant. Additionally, other metabolic modifications such as hydroxylation, conjugation, epimerization, and oxidation are occurring; and as the level of the 26-hydroxyecdysone 26-phosphate decreases there is a progression of other ecdysteroids. C-20 hydroxylation first appears in 24–40-h-old eggs and reaches peak activity in 48–64-h-old eggs, where 20-hydroxyecdysone and 20, 26-dihydroxyecdysone are both present at peak titer but the latter is the major free ecdysteroid. Ecdysone is observed at measurable levels only in the three age groups of eggs between 1 and 64 h-old. C-3 epimerase activity also appears at 24–40 h and continually increases throughout embryogenesis to the point that 3-epi-26-hydroxyecdysone and 3-epi-20, 26-dihydroxyecdysone are the major free ecdysteroids in 96-h-old eggs. A new ecdysteroid conjugate, 26-hydroxyecdysone 22-glucoside, first appears at 24–40h and becomes the major conjugate in 72–80-h-old eggs; it represents an apparent end-product as its peak titer is reached and maintained throughout the final embryonic stages. 20-Hydroxyecdysonoic acid occurs in 48–64-h-old eggs, and along with 3-epi-20-hydroxyecdysonoic and ecdysonoic acids in 72–88-h-old eggs. 20-Hydroxyecdysonoic acid peaks during the latter time interval, and as its titer subsequently falls, there is a concurrent increase in the level of 3-epi-20-hydroxyecdysonoic which was identified as the second major component of the ecdysteroid conjugate fraction of 0–1-h-old larvae. Our results indicate that there is little or no biosynthesis of ecdysteroids during embryogenesis; that the materal ecdysteroid conjugate 26-hydroxyecdysone 26-phosphate serves as source for 26-hydroxyecdysone and the numerous metabolites; that 26-hydroxyecdysone and 20,26-dihydroxyecdysone may be the active hormones during embryonic development; and that glucosylation, epimerization, and formation of acids cosntitute inactivation processes. A scheme of the proposed pathways involved in the metabolism of 26–hydroxyecdysone 26-phosphate in the developing eggs of m. sexta is presented.     

The ecdysteroids from young embryonated eggs of the tobacco hornworm

26-Hydroxyecdysone, which is the major free recoverable ecdysteroid of older age groups of embryonated eggs of the tobacco hornworm was also the major component in 4- to 18-hour-old embryonated eggs. The other 3β-ecdysteroids, ecdysone, 20-hydroxyecdysone, and 20,26-dihydroxy-ecdysone, were also present and accounted for an the molting hormone activity; 26-hydroxyecdysone was devoid of molting hormone activity in the house fly assay. 20-Hydroxyecdysone was a minor component, which confirms the earlier observations that the main metabolic route for ecdysteroids during embryonic development is that leading to 26-hydroxy-ecdysone, whereas formation of 20-hydroxyecdysone is a minor pathway. A new 3α-ecdysteroid, 3-epi-26-hydroxyecdysone, also devoid of molting hormone activity, was the second major ecdysteroid isolated from the eggs. 3-Epi-20,26-dihydroxyecdysone was detected in very minute amounts. In additon to the six 3β-and 3α-ecdysteroids there were at least an equivalent number of unknown ecdysteroids an of which lacked molting hormone activity. Their physical properties including chromatographic behavior are discussed.     

A possible role of 20-hydroxyecdysone in embryonic development of the silkworm Bombyx mori

It has been well established that eggs of insects, including those of the silkworm Bombyx mori, contain various ecdysteroids and the amounts of these ecdysteroids fluctuate during embryonic development. In order to know the function of egg ecdysteroids in embryonic development of B. mori, we examined the biological activities of various egg ecdysteroids by in vitro ligand-binding assay and bioassay using B. mori eggs. First, using the ecdysteroid receptor of B. mori (BmEcR-B1/BmUSP heterodimer) prepared by yeast and Escherichia coli expression systems, the interaction between the ecdysteroid receptor and various egg ecdysteroids of B. mori was analyzed. The relative binding affinities of egg ecdysteroids to the BmEcR-B1/BmUSP heterodimer decreased in the order of 20-hydroxyecdysone > 2-deoxy-20-hydroxyecdysone > 22-deoxy-20-hydroxyecdysone > ecdysone > 2-deoxyecdysone > ecdysone 22-phosphate. Next, several egg ecdysteroids of B. mori were injected into the prospective diapause eggs, which show a very low level of free ecdysteroids at the onset of embryonic diapause (gastrula stage). Approximately 7% of them (P < 0.002, chi(2)-test) developed beyond the gastrula stage without entering diapause by the injection of 20-hydroxyecdysone (25 ng/egg). In contrast, the injection of other ecdysteroids was not effective in inducing embryonic development. These results suggest that 20-hydroxyecdysone, via the ecdysteroid receptor, is responsible for the developmental difference between diapause and non-diapause in B. mori embryos. Furthermore, it was suggested that continuous supply of 20-hydroxyecdysone may be required to induce embryonic development.     

Ecdysteroids in developing ovaries and eggs of the tobacco hornworm

Ecdysteroids of ovaries and newly-laid eggs (0- to 1-hour-old) of the tobacco hornworm are present mainly as conjugates (greater than 95%). Newly-laid eggs contain ecdysteroid conjugates equivalent to 21 micrograms of 26-hydroxyecdysone and 0.73 micrograms of ecdysone per gram of eggs. These levels are similar in ovaries of 93-hour-old adult females. In 1- to 18-hour-old eggs more than 63% of the ecdysteroids exist in the free form and the proportion is similar in 48- to 64-hour-old eggs. The ratio of 26-hydroxyecdysone to ecdysone in the conjugated form remains constant during oocyte maturation and embryogenesis. Though 26-hydroxyecdysone is without molting hormone activity in the house fly assay, the exceptionally high concentration of 26-hydroxyecdysone conjugate(s) in ovaries and newly-laid eggs, together with the fact that it is being released during embryogenesis, indicate some physiological role for 26-hydroxyecdysone.     

Ecdysteroids in Carausius eggs during embryonic development

Peaks of ecdysteroids were observed during the different phases of embryonic development of intact Carausius eggs or eggs precociously deprived of their exochorion and cultivated under paraffin oil. Several groups of ecdysteroids were separated and analyzed by thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC) combined with radioimmunoassay. Ecdysteroids were similar in the two categories of eggs, including high-polarity products (essentially conjugates hydrolyzable by Helix pomatia digestive juice, or alkaline phosphatase), possible ecdysonoic acids (unhydrolyzable polar substances), free hormones, and nonpolar ecdysteroids. Four ecdysteroids were identified by co-elution during HPLC with reference compounds of 20,26-dihydroxyecdysone, 20-hydroxyecdysone, ecdysone, and 2-deoxy-20-hydroxyecdysone. Concentrations of these substances (free and conjugated forms) were studied during the different stages of embryonic development: 20-hydroxyecdysone and 2-deoxy-20-hydroxyecdysone were the major free ecdysteroids. They showed parallel variations with large peaks at stages VI₈ and VII₆ whereas ecdysone titers were consistently low. Injected labelled ecdysone was converted efficiently into 20-hydroxyecdysone, and both compounds underwent 26-hydroxylation and/or conjugation to polar or apolar metabolites.     

Growth-promoting effects of ecdysteroids and juvenile hormone on in vitro development of the larval endoparasitoid,Venturia canescens (Hymenoptera: Ichneumonidae)

We previously reported that lipophorin, fetal bovine serum (FBS), and 20-hydroxyecdysone (20-HE) are essential for the development of the larval endoparasitoid Venturia canescens larvae in vitro. The present study was undertaken to determine the optimal concentrations of those three substances in the MGM-450 medium, and to examine the hormonal effects of ecdysteroids and juvenile hormone (JH) on the development of the parasitoid larvae in vitro. When the culture was started with embryos at the post-germband stage, concentrations of 3 mg/ml of lipophorin and 20% of FBS were most suitable for the development of the parasitoid. The growth-promoting effect of 20-HE increased in a concentration-dependent manner and peaked at a concentration of 1 &mgr;g/ml. Excess concentration led to malformations of the larvae. Three other ecdysteroids, ecdysone, 2-deoxy-20-hydroxyecdysone, and polypodine B had the same effect, although their activity was lower than that of 20-HE. Cholesterol had no effect; most larvae failed to develop. When the medium was supplemented with JH, the duration of the developmental period was significantly shortened, but this hormone was not found to be essential.     

Crustacean ecdysteriods in reproduction and embryogenesis

Ecdysteroids are the molting hormones in Crustacea, as in other arthropods. They also subserve functions in the control of reproduction and embryogenesis. The available evidence indicate that the ecdysteroids are sequestered into the ovary by binding to yolk precursor proteins. Steroidogenic ability of the ovary is yet to be demonstrated in Crustacea. Despite several investigations, the role of ecdysteroids in oocyte maturation is not fully known. However, the embryonic ecdysteroids undergo significant fluctuation, correlated to specific developmental stages, including the secretion of embryonic envelopes and cuticle. Ecdysteroid metabolism in the eggs seems to be active throughout embryogenesis inasmuch as the free ecdysteroids are rapidly converted into conjugates, and vice versa; in addition to their inactivation into excretory ecdysteroidic acids. Eyestalk neuropeptides such as molt inhibiting hormones have a dominant role on the ecdysteroid synthesis by Y-organ, although recent evidence suggests a stimulatory role for yet another endocrine gland, the mandibular organ on Y-organ synthesis.     

Ecdysteroids During Embryogenesis in Locusta migratoria

SYNOPSIS. Ovaries of Locusta migratoria synthesize large amountsof ecdysteroids at the end of oöcyte maturation. The predominantecdysteroids in mature ovaries are conjugated 2-deoxyecdysone(100 µM) and conjugated ecdysone (50 µM) which outnumberthe corresponding free compounds by 50–100 fold. Thesevarious ecdysteroids persist during ovulation and are recoveredfrom newly-laid eggs. The conjugated maternal ecdysteroids aregradually metabolized as embryonic development proceeds; theyhave disappeared as such on day 6 after oviposition, that isafter blastokinesis and shortly after dorsal closure. Concomitantlyto this metabolism of the maternal conjugated ecdysteroids,other ecdysteroid conjugates appear in the eggs which have differentchromatographic behaviors and some of which are conjugates ofecdysone metabolites formed by the embryo. The data availableso far are compatible with the hypothesis that the maternalconjugates are hydrolysed to free 2-deoxyecdysone and ecdysoneby the embryo during early stages of development and subsequentlyconjugated to inactivation compounds. During the later stagesof embryonic development however, a de novo synthesis of ecdysoneis probable, the maternal conjugates having been metabolizedduring the earlier stages.     

Investigations on ecdysteroids and juvenile hormones and on morphological aspects during early embryogenesis in the ovoviviparous cockroach Nauphoeta cinerea

During early embryogenesis, which is from ovulation (day 0) until dorsal closure (day 19), the quantity of free and conjugated ecdysteroids in the egg cases, as measured by radioimmunoassay (RIA), increases. Thin-layer chromatography (TLC) and high-performance-liquid-chromatography (HPLC) analyses combined with RIA suggest that 20-hydroxy-ecdysone is the predominant ecdysteroid. Hydrolysis of the highly polar products of day-0 and day-17 egg cases by Helix pomatia enzymes indicates the presence of some conjugates of 20-hydroxy-ecdysone, hydrolyzable under these conditions. However, important quantities of RIA-reactive highly polar products are not hydrolyzed particularly in day-17 egg cases. These results demonstrate that the highly polar products of day-0 egg cases are qualitatively as well as quantitatively different from the highly polar products of day-17 egg cases. Morphological investigations show that the peak of 20-hydroxy-ecdysone at the time of the dorsal closure coincides with the synthesis of an embryonic cuticle. Using the Galleria wax test only traces, or no juvenile hormone activity could be detected in embryos during the entire period of early embryonic development. Morphological investigations of the brood sac suggest that this organ is very important to facilitate the initial uptake of water into the eggs. Thereafter the embryos can develop independently of the female when kept in a humid environment.     

The effect of manipulating ecdysteroid signaling on embryonic eye development in the locust<Emphasis Type="Italic"> Schistocerca americana</Emphasis>

Adult body plan differentiation in holometabolous insects depends on global induction and control by ecdysteroid hormones during the final phase of postembryogenesis. Studies in Drosophila melanogaster and Manduca sexta have shown that this pertains also to the development of the compound eye retina. It is unclear whether the hormonal control of postembryonic eye development in holometabolous insects represents evolutionary novelty or heritage from hemimetabolous insects, which develop compound eyes during embryogenesis. We therefore investigated the effect of manipulating ecdysteroid signaling in cultured embryonic eye primordia of the American desert locust Schistocerca americana, in which ecdysteroid level changes are known to induce three rounds of embryonic molt. Although at a considerably reduced rate compared to in vivo development, early differentiation and terminal maturation of the embryonic retina was observed in culture even if challenged with the ecdysteroid antagonist cucurbitacin B. Supplementing cultures with 20-hydroxyecdysone (20E) accelerated differentiation and maturation, and enhanced cell proliferation. Considering these results, and the relation between retina differentiation and ecdysteroid level changes during locust embryogenesis, we conclude that ecdysteroids are not an essential but possibly a modulatory component of embryonic retina development in S. americana. We furthermore found evidence that 20E initiated precocious epithelial morphogenesis of the posterior retinal margin indicating a more general role of ecdysteroids in insect embryogenesis.Electronic Supplementary Material Supplementary material is available in the online version of this article at Edited by C. Desplan     

Embryonic ecdysteroids in a mole crab,Emerita asiatica (Milne-Edwards)

Using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC), the presence of a complex mixture of free and conjugated ecdysteroids is reported in the embryonated eggs of a mole crab,Emerita asiatica. From an initial low value of 6.5 ng/g egg wet weight in stage I, the total ecdysteroids increased in concentration to 15.2 ng/g egg wet weight in stage III. This was followed by a sharp fall in stage IV, but again increased to 15.0 ng/g egg wet weight in stage VI. After a further decline in stage VII, the total ecdysteroids registered the highest value of 36.2 ng/g egg wet weight in stage VIII. This value, however, declined to a low level in the prehatching stage (IX). The concentration of the free ecdysteroids always predominated over the conjugated ones. The HPLC analysis of free ecdysteroids demonstrated the presence of 20-hydroxyecdysone and ecdysone in the ratio of 2.5. Purified lipovitellin II also contained free and conjugated ecdysteroids. The functional significance of the embryonic ecdysteroids as well as their nature of synthesis and storage within the eggs is discussed in the light of the information available on insect embryogenesis.     

The ecdysteroids from the tobacco hornworm during pupal-adult development five days after peak titer of molting hormone activity.

Six naturally occurring C27 ecdysteroids were isolated and identified from the tobacco hornworm during pupal-adult development five days after peak titer of molting hormone activity. In order of decreasing quantities the hormones were: 20,26-dihydroxyecdysone, 3-epi-20-hydroxyecdysone, 20hydroxyecdysone, 3-epi-20,26-dihydroxyecdysone, 3-epi-ecdysone, and ecdysone. 20-Hydroxyecdysone, in an earlier study, was the major molting hormone present at peak titer during pupal-adult development. The major ecdysteroid present during embryonic development in this insect, 26-hydroxyecdysone, was not detected. The copresence of all six of these ecdysteroids from a single developmental stage of an insect provides information on the metabolic interrelationships that exist among these steroids and on their possible function(s) in insects. The 3alpha-ecdysteroids were far less active than the 3 beta-epimers in the house fly assay. The significance of epimerization is discussed.     

Sécrétions cuticulaires et ecdystéroïdes chez les embryons decapités du phasme Carausius morosus Br. / Ecdysteroids and cuticle secretions in decapitated embryos of the phasmid Carausius morosus Br.

Summary

Embryos of the phasmid Carausius morosus Br., deprived of their head at an early stage (V₃, 27th day) of development live up to the 147th day when grown on their own vitello-serosal system.

In these embryos, the 2nd embryonic cuticle characteristic of the dorsal closure stage, and the 3rd embryonic cuticle (1st larval cuticle) with its setae and procuticle, both have a typical structure. Thus the cephalic endocrine system of the embryo is clearly not indispensable either for 2nd and 3rd cuticle deposition, or for production of a typical ecdysteroid peak at the dorsal closure, or even for the rise of ecdysteroid level during the 3rd cuticle secretion. But in decapitated embryos this rise is not followed by a decrease as it is in controls.

In both operated eggs and controls, the same free and conjugated 3 hormones were separated by HPLC and quantified by RIA: 20,26-dihydroxyecdysone, 20-hydroxyecdysone (main hormone in the phasmid) and ecdysone.

Very similar quantitative results were obtained for controls and operated eggs at the dorsal closure stage. However, noteworthy differences were found between the two kinds of eggs concerning the respective levels of 20-hydroxyecdysone and of its conjugates during the 3rd cuticle secretion.