Effects of juvenile hormone on the programming of postembryonic development in eggs of the silkworm, Hyalophora cecropia

Biological effects of some natural and chemical compounds on the potato tuber moth, Phthorimaea operculella Zell. (Lepidoptera:Gelechiidae)

The olfactory reaction of larvae and moths was investigated towards 18 oils (6 natural oils and 12 commercial chemical oils). Some of these oils such as peppermint and camphor (natural oils) and eugenol and camphene (commercial oils) were repellent to both larvae and moths. Other oils such as strawberry and d-limonene were attractive to both larvae and moths. Some of the repellent oils were, therefore, tested for their effect on certain biological aspects of the insects. Eugenol and peppermint oils, each at the 0.01% conc., caused a significant depression in the fecundity of moth and decreased the percentage of egg hatchability. Eugenol oil was much more effective than peppermint oil at 1%. Dried (leaves, fruits or seeds) powder of 14 different plants species were tested in different concentrations with talcum powder (carrier material) against egg deposition. The results indicated that dried powders of Allium cepa, Curcuma longa, Colocasia antiqurum, Ocimum basilicum. Dodonaea viscose and Thuja orientalis played a highly significant role in reducing egg deposition. The most impressive effect was displayed by powders of D. viscose and A. cepa, which caused the highest depression in egg deposition as well as in the emerging offsprings. Ethanolic extracts of 11 plants indicated that extracts of Pithuranthos tortosus and Iphiona scabra caused the maximum inhibition of egg hatchability, followed by C. longa, Citrullus colocynthia and T. orientalis. Ethanolic extracts of Schinus terebenthiflius (leaves) and I. scabra caused the highest depression in the deposited eggs, as they played a remarkable role as ovipositor deterrents. The majority of the plant extracts at 1% conc. could protect potato tubers at different intervals according to the calculated tuber damage index as follows: Iphiopna > Pithuranthos > Curcuma > Schinus (fruits) Thuja > Schinus (leaves) > Dodonaea > Citrullus.

Unscrambling butterfly oogenesis

Background

Butterflies are popular model organisms to study physiological mechanisms underlying variability in oogenesis and egg provisioning in response to environmental conditions. Nothing is known, however, about; the developmental mechanisms governing butterfly oogenesis, how polarity in the oocyte is established, or which particular maternal effect genes regulate early embryogenesis. To gain insights into these developmental mechanisms and to identify the conserved and divergent aspects of butterfly oogenesis, we analysed a de novo ovarian transcriptome of the Speckled Wood butterfly Pararge aegeria (L.), and compared the results with known model organisms such as Drosophila melanogaster and Bombyx mori.

Results

A total of 17306 contigs were annotated, with 30% possibly novel or highly divergent sequences observed. Pararge aegeria females expressed 74.5% of the genes that are known to be essential for D. melanogaster oogenesis. We discuss the genes involved in all aspects of oogenesis, including vitellogenesis and choriogenesis, plus those implicated in hormonal control of oogenesis and transgenerational hormonal effects in great detail. Compared to other insects, a number of significant differences were observed in; the genes involved in stem cell maintenance and differentiation in the germarium, establishment of oocyte polarity, and in several aspects of maternal regulation of zygotic development.

Conclusions

This study provides valuable resources to investigate a number of divergent aspects of butterfly oogenesis requiring further research. In order to fully unscramble butterfly oogenesis, we also now also have the resources to investigate expression patterns of oogenesis genes under a range of environmental conditions, and to establish their function.

How clocks and hormones act in concert to control the timing of insect development

During the last century, insect model systems have provided fascinating insights into the endocrinology and developmental biology of all animals. During the insect life cycle, molts and metamorphosis delineate transitions from one developmental stage to the next. In most insects, pulses of the steroid hormone ecdysone drive these developmental transitions by activating signaling cascades in target tissues. In holometabolous insects, ecdysone triggers metamorphosis, the remarkable remodeling of an immature larva into a sexually mature adult. The input from another developmental hormone, juvenile hormone (JH), is required to repress metamorphosis by promoting juvenile fates until the larva has acquired sufficient nutrients to survive metamorphosis. Ecdysone and JH act together as key endocrine timers to precisely control the onset of developmental transitions such as the molts, pupation, or eclosion. In this review, we will focus on the role of the endocrine system and the circadian clock, both individually and together, in temporally regulating insect development. Since this is not a coherent field, we will review recent developments that serve as examples to illuminate this complex topic. First, we will consider studies conducted in Rhodnius that revealed how circadian pathways exert temporal control over the production and release of ecdysone. We will then take a look at molecular and genetic data that revealed the presence of two circadian clocks, located in the brain and the prothoracic gland, that regulate eclosion rhythms in Drosophila. In this context, we will also review recent developments that examined how the ecdysone hierarchy delays the differentiation of the crustacean cardioactive peptide (CCAP) neurons, an event that is critical for the timing of ecdysis and eclosion. Finally, we will discuss some recent findings that transformed our understanding of JH function.

Role of juvenile hormone esterase and epoxide hydrolase in reproduction of the cotton bollworm, Helicoverpa zea

The role of juvenile hormone (JH) esterase (JHE) and epoxide hydrolase (EH) in reproduction of the cotton bollworm, Helicoverpa zea, was investigated. Peak emergence of male and female bollworm adults occurred early in the scotophase. Female adults were added to males in a 1:2 ratio, respectively, at the beginning of the first photophase after emergence (d0). The highest oviposition rates for mated females were noted on d 2-4. The in vitro JH III esterase and JH III EH activity was measured in whole body homogenates of virgin and mated females from d0 to d8 post-emergence. Maximal JHE activity for virgin females occurred on d2 (1.09+/-0.14(+/-1 SEM) nmol of JH III degraded/min/mg protein), which was approximately twice that of mated females on the same day. The same results were observed for EH where the activity peaked on d2 at 0.053+/-0.003 as compared to 0.033+/-0.003 nmol of JH III degraded/min/mg protein, respectively. By d4, both JHE and JH EH activities declined significantly in virgin and mated females and were the same through d7. The developmental changes and effects of mating on JH degradation were similar when measured per insect. The highest levels of JHE and JH EH activity/min/mg protein in d2 virgin and mated females was found in ovaries followed by the carcass and then haemolymph; no EH activity was found in haemolymph as expected. For ovary, the JHE and JH EH activity was highest in virgin compared to mated females. The role of both enzymes in the regulation of reproduction is discussed.

Embryonic expression of juvenile hormone binding protein and its relationship to the toxic effects of juvenile hormone in Manduca sexta

The juvenile hormones (JHs) regulate a diverse array of insect developmental and reproductive processes. One molecular target of JH action is its transporter, hemolymph JH binding protein (hJHBP); in the larva of the tobacco hornworm, Manduca sexta, low doses of JH can immediately increase hJHBP gene expression. Less explored are the effects of JH on embryological development, where early hormonal treatment has been shown to affect embryonic development and pupation. This study examines the egg form of JHBP and its gene expression during embryogenesis of M. sexta, as well as the phenotypic effect JH treatment has on embryos and on JHBP gene expression. We here demonstrate that the preponderance of JHBP found in the egg is maternally derived and that the embryonic gene and protein appear identical to those found in the larva. Expression of the JHBP gene begins in both the embryo itself and extra-embryonic tissues 15 h after fertilization, long before emergence of a functional fat body and circulatory system. Topical application of low JH doses to early embryos resulted in larval abnormalities while high doses of the hormone induced embryonic mortality. These effects are not mediated through regulation of the JHBP gene, since embryonic expression appears invariant in response to JH challenge. The toxicity of JH is tightly correlated with the concentration of unbound hormone.

Stress-reactivity and juvenile hormone degradation in Drosophila melanogaster strains having stress-related mutations

Juvenile hormone (JH) degradation was studied under normal and stress conditions in young and matured females of Drosophila melanogaster strains having mutations in different genes involved in responses to stress It was shown that (1) the impairment in heat shock response elicits an alteration in stress-reactivity of the JH system; (2) the impairment JH reception causes a decrease of JH-hydrolysing activity and of stress-reactivity in young females, while in mature ones stress reactivity is completely absent; (3) the absence of octopamine results in higher JH-hydrolysis level under normal conditions and altered JH stress-reactivity; (4) the higher dopamine content elicits a dramatic decrease of JH degradation under normal conditions and of JH stress-reactivity. Thus, the impairments in any component of the Drosophila stress reaction result in changes in the reponse of JH degradation system to stress. The role of JH in the development of the insect stress reaction is discussed.

Stress-reactivity of a Drosophila melanogaster strain with impaired juvenile hormone action

Met(27) is a null allele of the Methoprene-tolerant gene of D. melanogaster that shows resistance to the toxic effects of both juvenile hormone (JH) and a JH analog, methoprene. The mechanism of resistance appears to be altered JH reception. We measured fertility, JH-hydrolyzing activity, and dopamine (DA) levels in Met(27) and Met(+) flies under normal (25 degrees C) and heat-stress (38 degrees C) conditions. We show that under normal conditions Met(27) females have JH-hydrolyzing activity and fertility lower than Met(+), but DA content did not differ between the two strains. At 38 degrees C Met(27) flies show no impairment in JH-hydrolyzing activity in response to stress, but they do show lower DA levels and impaired reproduction. The results with Met(27) are consistent with the previous hypothesis that the alteration in fertility that follows heat stress in D. melanogaster could result from alteration in the JH endocrine system.

Prolonged negative selection of Drosophila melanogaster for a character of adaptive significance disturbs stress reactivity

The metabolism of juvenile hormone by JH-esterase and JH-epoxide hydrolase, and octopamine by tyrosine decarboxylase were studied under normal and stress conditions in flies of two related lines of D. melanogaster. One was selected for high (HA line) and another for low (LA line) male sexual activity for more than 700 generations. It was demonstrated that prolonged selection for low male sexual activity results in considerable changes in both systems. Tyrosine decarboxylase activity in males and females of the LA line was sharply reduced as compared with those of the HA and control Canton-S lines; JH-esterase and JH-epoxide hydrolase activities were decreased in females, and not in males, of the LA line. It was demonstrated that the response of both metabolic systems to heat stress is impaired in individuals of the LA line: the system of juvenile hormone metabolism does not respond to stress, and that of octopamine metabolism is decelerated. The role of juvenile hormone metabolism in male reproductive function is discussed.

Bombyx mori development: the context for its endocrine system

Quantitative data on neurohormones (brain-hormones) steroïd hormones, juvenile hormones, in an insect : Bombyx mori are outlined. The variations of hormonal contents throughout larval and pupal development, in eggs and ovocytes are analyzed.

[Development of prospective diapause-germs (Bombyx mori L.)in vitro without dormancy : III. Their competence and interference inLYS-media, without extraembryonic storage material]

In a foreign protein medium (LTS), naked prospective diapause-germs have a tendency to develop into fully segmented germ bands (stage of dormancy): however, deposition of chorion, serosa or yolk will stimulate themvia the medium to pass through organogenesis without delay (non-dormancy =Nd). The question remained if a germ from a non-diapausing egg would stimulate the uninterrupted development of such a test-germ (Tk). Using 2 different or 2 to 3 equal germs as well asTk alone (control) in hanging drops, experimental evidence was obtained permitting conclusions not only as to the competence and sensitivity of the embryonic reaction system, but also as to factors of the extraembryonicNd-action systems in eggs with and without predetermined diapause regulatory mechanism. 1. Control explants (1 prospective diapause-Tk inLYS) have aNd-level of 10% (= average ofNd-rates in operative stages). This difference from former controls (0%Nd) can be explained by the longer operative procedure in the cups when several test-germs were used. Seven minutes after opening an egg one can reckon on aNd-stimulationvia LYS medium from egg-residues in the operation cup. While transfering the test-germs, yolk-derived substances related to theNd-stimulation can be brought into the hanging drop. The difference betweenNd-controls and the results ofNd-stimulation have to be statistically significant. 2. In experiments with two different germs in LYS-droplets no influence of a non-diapause germ (polyvoltine) on a prospective diapause germ (univoltine) could be noted. Accordingly, the naturally prospectiveNd-germs, have a tendency to develop to dormant germs only, as do the 2Tk and 1Tk controls. In combination with artificially prospectiveNd-germs (univoltine, HCl-treated) no stimulation of the test germ occcurs; nor after explantation with an older germ-band or a young embryo. 3. Combination with two prospective diapause germs of equal age in a drop, having the same minor contamination ofNd-factors in the operation-cup, will result in a threefold increase of theNd-level as compared to the 1Tk-controls. The competence of the embryonic reaction system ranges from a coatlike germ-anlage to a germ with thoracic segmentation. In the dish-like germ-anlage at diapause onsetin ovo maximalNd-rate (70%) is foundin vitro, i.e. highest sensibility towardsNd-stimulatory factors. Also at this operative stage, bothTk of a drop, most frequently developed beyond the dormancy stage. 4. Experiments with three prospective diapause germs of equal age in a drop, having the same minor contamination ofNd-factors in the operation-cup, show a sevenfold increase of theNd-level as compared to controls, showing an almost similar stage-range in competence and stage-specificity in sensibility. The increase of theNd-stimulation rate in relation with the number of test germs in the drop corresponds to a morphogenetic crowding-effect, the influence of the test germs on each other being called "interference". 5. Experiments with LYS-media which was slightly contaminated with bacteria and then refiltered had a 42%Nd-level in the 1Tk experiments. This significant difference from the 10% control level can be related to a sensitivity increasing factor or to aNd-stimulating "masterkey"-effect of the bacterial products in addition to the yolk factors already present. The 65%Nd-level in the 2Tk experiments clearly indicates "interference". 6. Interference was also shown inexperiments with artificially prospective non-diapause germ of the same age. Test-germs isolated immediately after the HCl-treatment had a very highNd-rate (78% in 2Tk and 100% in 3Tk). Interference also occurred in germ-bands that were removed at a later stage, i.e.in ovo prior to organogenesis (2Tk, 60%Nd-rate instead of 1Tk, 20%Nd-rate). Consequently, interference may be caused by a factor promoting an overall increase of tissue activity. 7. Critical evaluation of the methods and discussion of the resultsin vitro permit the following conclusions as to the developmentin ovo. Up to organogenesis, the continuous development of the germ-anlage (non-dormancy), is stimulated by an extra-embryonic system. In particular, the yolk-cell system contains factors, without which all germ-bands (including nondiapausal eggs fromBombyx and presumably other insect eggs) can only pass autonomously through the already programmed and/or determined gastrulation and segmentation. In pre-determined egg-diapause, an extra-embryonic dormancy regulatory mechanism inactivates thisNd-action system. Maternal hormonal depots may influence the continuous stimulation of cell division and the information-transfer for the programming of organogenesis. The activation of enzyme-systems inNd-stimulation can be imitatedin vitro by bacterial contamination and by interference from test germs of the same age, and may be appear as increased sensibility of the test germs.

Effect of juvenile hormone on DNA synthesis during embryogenesis inAcheta domesticus

1) The effect of juvenile hormone on embryonic development in the cricket,Acheta domesticus, was investigated. Application of 1 to 2.5 μg of methyl 12,14-dihomojuvenate (cecropia juvenile hormone) in 1 μl of acetone to 7-day-old cricket embryos inhibited their further growth. In such embryos, differentiation of some of the embryonic organs and tissues such as nerves, muscles and cuticular structures continued. However, embryonic growth was arrested, their morphology was abnormal and they failed to hatch. 2) Lipid extracts from adult maleHyalophora cecropia which possess juvenile hormone activity also showed similar effects on embryonic development. But lipid extracts prepared from allatectomized adult maleH. cecropia lacking juvenile hormone activity, did not inhibit embryonic development. 3) DNA synthesis in the embryonic tissues of the JH-treated and control embryos was investigated using an autoradiographic method of determination of H³ thymidine incorporation into nuclear DNA. The results showed that DNA synthesis in epidermal and mesenchymal cells of the cricket embryo decreased gradually after application of 1 μg of JH to 7-day-old embryos and ceased within 6 days after application of JH. 4) From these observations it is suggested that JH may inhibit embryonic development by suppression of DNA synthesis and cell divisions.

Prevention of Metamorphosis by Exposure of Insect Eggs to Juvenile Hormone Analogs

Metamorphosis of the bugs Pyrrhocoris apterus and Oncopeltus fasciatus is blocked by the application of juvenile hormone analogs to the eqgs 4 weeks earlier. One or more supernumerary larval molts occur to form "giant" larvae which routinely die without undergoing netamorphosis. When the corpora allatta were excised at the outset of the fifth larval stage, the entire phenomenon vanished and all individuals underwent normal metamorphosis. The inhibition of metamorphosis can therefoore be attributed to a continuation of the secretion of endogenous juvenile hormone by the corpora allata of mature larvae deried from eggs treated with juvenile hormone.