Effects of juvenile hormone on the secretion of prothoracicotropic hormone in the last- and penultimate-instar larvae of the silkworm Bombyx mori

Identification and expression profiling of neuropeptides and neuropeptide receptor genes in a natural enemy, Coccinella septempunctata

Introduction

Neuropeptides and their receptors constitute diverse and abundant signal molecules in insects, primarily synthesized and released primarily from neurosecretory cells within the central nervous system Neuropeptides act as neurohormones and euromodulators, regulating insect behavior, lifecycle, and physiology by binding to receptors on cell surface. As a typical natural predator of agricultural pests, the lady beetle, Coccinella septempunctata, has been commercially mass-cultured and widely employed in pest management. Insect diapause is a physiological and ecological adaptative strategy acquired in adverse environments. In biological control programs, knowledge about diapause regulation in natural enemy insects provides important insight for improving long-term storage, transportation, and field adoption of these biological control agents. However, little is known about the function of neuropeptides and their receptors in controlling reproductive diapause of C. septempunctata. It is unclear which neuropeptides affect diapause of C. septempunctata.

Methods

In this study, RNA-seq technology and bioinformatics were utilized to investigate genes encoding neuropeptides and their receptors in female adults of C. septempunctata. Quantitative real-time PCR (qRT-PCR) analysis was employed to examine gene expression across different development/diapause stages.

Results

A total of 17 neuropeptide precursor genes and 9 neuropeptide receptor genes were identified, implicated in regulating various behaviors such as feeding, reproduction, and diapause. Prediction of partial mature neuropeptides from precursor sequences was also performed using available information about these peptides from other species, conserved domains and motifs. During diapause induction, the mRNA abundance of AKH was notably higher on the 10th day compared to non-diapause females, but decreased by the 20th day. In contrast, GPHA showed lower expression levels on the 5th day of diapause induction compared to non-diapause females, but increased significantly by the 15th and 20th days. NPF was higher expressed in head and midgut while DH showed higher expression in the fat body and midgut. Additionally, NPF expression remained consistently lower throughout all stages of diapause induction compared to non-diapause conditions in females.

Discussion

This study represents the first sequencing, identification, and expression analysis of neuropeptides and neuropeptide receptor genes in C. septempunctata. Our results could provide a foundational framework for further investigations into the presence, functions, and potential targets of neuropeptides and their receptors, particularly in devising novel strategies for diapause regulation in C. septempunctata.

Investigating the Regulatory Mechanism of the Sesquiterpenol Nerolidol from a Plant on Juvenile Hormone-Related Genes in the Insect Spodoptera exigua

Various plant species contain terpene secondary metabolites, which disrupt insect growth and development by affecting the activity of juvenile hormone-degrading enzymes, and the juvenile hormone (JH) titers maintained in insects. Nerolidol, a natural sesquiterpenol belonging to the terpenoid group, exhibits structural similarities to insect JHs. However, the impact of nerolidol on insect growth and development, as well as its underlying molecular mechanism, remains unclear. Here, the effects of nerolidol on Spodoptera exigua were investigated under treatment at various sub-lethal doses (4.0 mg/mL, 1.0 mg/mL, 0.25 mg/mL). We found that a higher dose (4.0 mg/mL) of nerolidol significantly impaired the normal growth, development, and population reproduction of S. exigua, although a relatively lower dose (0.25 mg/mL) of nerolidol had no significant effect on this growth and development. Combined transcriptome sequencing and gene family analysis further revealed that four juvenile hormone esterase (JHE)-family genes that are involved in juvenile hormone degradation were significantly altered in S. exigua larvae after nerolidol treatment (4.0 mg/mL). Interestingly, the juvenile hormone esterase-like (JHEL) gene Sexi006721, a critical element responsive to nerolidol stress, was closely linked with the significant augmentation of JHE activity and JH titer in S. exigua (R2 = 0.94, p < 0.01). Taken together, we speculate that nerolidol can function as an analog of JH by modulating the expression of the enzyme genes responsible for degrading JH, resulting in JH disorders and ultimately disrupting the development of insect larvae. This study ultimately provides a theoretical basis for the sustainable control of S. exigua in the field whilst proposing a new perspective for the development of novel biological pesticides.

Larval feeding status regulates the transcript levels of genes encoding PTTH and allatoregulatory peptides in silkworm Bombyx mori

In Bombyx mori, two dorsolateral neurosecretory cells (NSCs) in each of the two brain lobes have been identified as prothoracicotropic hormone (PTTH) producing cells. This neuropeptide in insects stimulates the prothoracic gland for the synthesis and release of ecdysone, responsible for the molting events. Allatotropin (AT) and allatostatin (AST) are allatoregulatory neuropeptides that regulate juvenile hormone biosynthesis. Here, by using RT-qPCR, we showed that in B. mori, nutritional stress modulates the mRNA expression of AT and AST-C (allatostain type C) in the central nervous system consisting of the brain lobes and all the associated ganglia. Using whole-mount in situ hybridization, we showed that the feeding status of Bombyx larvae also influences the expression of PTTH in the NSCs of the brain. Food deprivation significantly decreased the mRNA expression levels of PTTH in larvae at active or terminal growth period. Further, we showed that insulin modulates the expression level of PTTH. However, its action was dependent on the feeding status of the larvae. At feeding, the insulin decreased the PTTH expression level, while at food deprivation, the insulin increased the PTTH expression level. The data thus indicates that larval feeding status plays an important role in altering the mRNA expression levels of allatoregulatory peptide genes and PTTH.

Endocrine Disruptor Exposure Causes Infochemical Dysregulation and an Ecological Cascade from Zooplankton to Algae

Endocrine disruption is intimately linked to controlling the population of pollutant-exposed organisms through reproduction and development dysregulation. This study investigated how endocrine disruption in a predator organism could affect prey species biology through infochemical communication. Daphnia magna and Chlorella vulgaris were chosen as model prey and predator planktons, respectively, and fenoxycarb was used for disrupting the endocrine system of D. magna. Hormones as well as endo- and exometabolomes were extracted from daphnids and algal cells and their culture media and analyzed using liquid chromatography with tandem mass spectrometry. Biomolecular perturbations of D. magna under impaired offspring production and hormone dysregulation were observed. Differential biomolecular responses of the prey C. vulgaris, indicating changes in methylation and infochemical communication, were subsequently observed under the exposure to predator culture media, containing infochemicals released from the reproducibly normal and abnormal D. magna, as results of fenoxycarb exposure. The observed cross-species transfer of the endocrine disruption consequences, initiated from D. magna, and mediated through infochemical communication, demonstrates a novel discovery and emphasizes the broader ecological risk of endocrine disruptors beyond reproduction disruption in target organisms.

RNA interference-mediated knockdown of some genes involved in digestion and development of Helicoverpa armigera

Helicoverpa armigera is a significant agricultural pest and particularly notorious for its resistance to many types of common insecticides. RNA interference (RNAi) is a mechanism of post-transcriptional gene silencing and trigged by double-strand RNA (dsRNA), has become a widely used reverse genetics and potent tool for insect pest control. In this study, the effect of ingestion and injection delivery methods of dsRNA related two important enzyme genes, α-amylase (HaAMY48, Ha-AMY49) and juvenile hormone esterase (Ha-JHE), were examined on growth and development of H. armigera. After 24, 48, 72 and 96 h of feeding bioassay, significant down regulation was observed about; 56, 68, 78, 80.75% for HaAMY48, 60, 70, 86.5 and 96.75%, for Ha-AMY49 and 14, 27.5, 23 and 31.7% for Ha-JHE, respectively. The results for injection assay was 61.5, 71.5, 74 and 95.8% for Ha-AMY48; 70, 88, 91.5 and 97.7% for Ha-AMY49 and 22, 61, 75 and 74% for Ha-JHE after 24, 48 and 72 h of last injecting, respectively. Larvae that treated with dsRNA, fed or injected, lost more than half of their weight. 50% mortality in treated larvae was observed in the case injection bioassay with dsHa-JHE and 59% of larvae that fed of dsRNA-treated cubes survived. DsHa-AMY48 and 49 have significant mortality, but mixing of them is more effective in both bioassays. Injection bioassay has a potent inhibitory effect on α-amylase-specific activity about more than 87% in treated larvae with mix of dsHa-AMY48 and 49. Adult malformation percent was evaluated for feeding (28, 35.5 and 43% for Ha-AMY48, 49 and Ha-JHE, respectively) and injection bioassay (23, 42 and 29% for Ha-AMY48, 49 and Ha-JHE, respectively). All these finding suggest that Ha-AMY48, Ha-AMY49 and Ha-JHE can be new candidates to scheming effective dsRNAs pesticide for H. armigera control.

Identification and characterization of genes involving the early step of Juvenile Hormone pathway in Helicoverpa armigera

Juvenile hormones (JHs) are crucial regulators for multiple physiological processes in insects. In the current study, 10 genes in mevalonate pathway involved in JH biosynthesis were identified from Helicoverpa armigera. Tissue-specific expression analysis showed that six genes were highly expressed in the head which contained the JH biosynthetic gland (corpora allata). Temporal expression pattern showed that 10 of 12 genes were highly transcribed in the late 2^nd-instar when the in vivo JH titer reached the peak, indicating a tight correlation between JH titer and the transcription of JH synthetic pathway genes. Moreover, ingestion of methoprene, a JH analogue, significantly suppressed the transcription of nine JH biosynthetic genes and caused a feedback upregulation of the JH degradation enzyme. Particularly, the Acetoacetyl CoA thiolase (HaAce) and Farnesyl diphosphate synthase gene 4 (HaFpps4) showed high transcript abundance, and their temporal expressions keep pace with JH fluctuations. Further study by RNAi showed that knockdown of HaFpps4 caused the decrease of JH titer, led to a negative effect on the transcript levels of other genes in JH pathway, and resulted in molting disturbance in larvae. Altogether, these results contribute to our understanding of JH biosynthesis in H. armigera and provide target genes for pest control based on JH-dependent regulation.

Homeodomain Protein Scr Regulates the Transcription of Genes Involved in Juvenile Hormone Biosynthesis in the Silkworm

The silkworm Dominant trimolting (Moltinism, M³) mutant undergoes three larval molts and exhibits precocious metamorphosis. In this study, we found that compared with the wild-type (WT) that undergoes four larval molts, both the juvenile hormone (JH) concentration and the expression of the JH-responsive gene Krüppel homolog 1 (Kr-h1) began to be greater in the second instar of the M³ mutant. A positional cloning analysis revealed that only the homeodomain transcription factor gene Sex combs reduced (Scr) is located in the genomic region that is tightly linked to the M³ locus. The expression level of the Scr gene in the brain-corpora cardiaca-corpora allata (Br-CC-CA) complex, which controls the synthesis of JH, was very low in the final larval instar of both the M³ and WT larvae, and exhibited a positive correlation with JH titer changes. Importantly, luciferase reporter analysis and electrophoretic mobility shift assay (EMSA) demonstrated that the Scr protein could promote the transcription of genes involved in JH biosynthesis by directly binding to the cis-regulatory elements (CREs) of homeodomain protein on their promoters. These results conclude that the homeodomain protein Scr is transcriptionally involved in the regulation of JH biosynthesis in the silkworm.

Positive feedback regulation of prothoracicotropic hormone secretion by ecdysteroid--a mechanism that determines the timing of metamorphosis

When insect larvae have fully grown, prothoracicotropic hormone (PTTH) is released from the brain, triggering the initiation of metamorphic development through stimulation of ecdysteroid secretion by the prothoracic glands. The present study analyzes the mechanism that regulates the occurrence of this PTTH surge. In the silkworm Bombyx mori, the PTTH surge occurs on day 6 of the fifth instar and is preceded by a small rise in hemolymph ecdysteroid titer, which occurs late on day 5. We therefore hypothesized that this rise of ecdysteroid titer is involved in the induction of the PTTH surge. To test this hypothesis, two experiments were conducted. First, a small amount of 20-hydroxyecdysone was injected on day 4, two days before the expected day of the PTTH surge, to simulate the small rise in hemolymph ecdysteroid titer on day 5. This injection led to a precocious surge of PTTH the next day. Next, the hemolymph ecdysteroid titer on day 5 was artificially lowered by injecting ecdysteroid-22-oxidase, which inactivates 20-hydroxyecdysone. After this treatment, the PTTH surge did not occur on day 6 in 80% of the animals. These results indicate that a small rise of the hemolymph ecdysteroid titer plays a critical role in the induction of the PTTH surge. Since basal ecdysteroidogenic activity of the prothoracic glands increases with larval growth, a circulating level of ecdysteroids may convey information about larval maturity to the brain, to coordinate larval growth and metamorphosis. This is the first report in invertebrates to demonstrate positive feedback regulation of the surge of a tropic hormone by a downstream steroid hormone.

Microarray Analysis of the Juvenile Hormone Response in Larval Integument of the Silkworm, Bombyx mori

Juvenile hormone (JH) coordinates with 20-hydroxyecdysone (20E) to regulate larval growth and molting in insects. However, little is known about how this cooperative control is achieved during larval stages. Here, we induced silkworm superlarvae by applying the JH analogue (JHA) methoprene and used a microarray approach to survey the mRNA expression changes in response to JHA in the silkworm integument. We found that JHA application significantly increased the expression levels of most genes involved in basic metabolic processes and protein processing and decreased the expression of genes associated with oxidative phosphorylation in the integument. Several key genes involved in the pathways of insulin/insulin-like growth factor signaling (IIS) and 20E signaling were also upregulated after JHA application. Taken together, we suggest that JH may mediate the nutrient-dependent IIS pathway by regulating various metabolic pathways and further modulate 20E signaling.

Functional characterization of a juvenile hormone esterase related gene in the moth Sesamia nonagrioides through RNA interference

Juvenile hormone esterase (JHE) is a carboxylesterase that has attracted great interest because of its critical role in regulating larval to adult transition in insects and other arthropods. Previously, we characterized an ecdysteroid sensitive and juvenile hormone non-susceptible juvenile hormone esterase related gene (SnJHER) in the corn stalk borer, Sesamia nonagrioides. SnJHER was rhythmically up-regulated close to each molt during the corn stalk borer's larval development. In this paper we attempted to functionally characterize SnJHER using several reverse genetics techniques. To functionally characterize SnJHER, we experimented with different dsRNA administration methods, including hemolymph, bacterial or baculovirus-mediated RNA interference, (RNAi). Our findings indicate the potential implication of SnJHER in the developmental programming of Sesamia nonagrioides. It is still unclear whether SnJHER is closely related to the authentic JHE gene, with different or similar biological functions.

Ecdysone control of developmental transitions: lessons from Drosophila research

The steroid hormone ecdysone is the central regulator of insect developmental transitions. Recent new advances in our understanding of ecdysone action have relied heavily on the application of Drosophila melanogaster molecular genetic tools to study insect metamorphosis. In this review, we focus on three major aspects of Drosophila ecdysone biology: (a) factors that regulate the timing of ecdysone release, (b) molecular basis of stage- and tissue-specific responses to ecdysone, and (c) feedback regulation and coordination of ecdysone signaling.

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.

Molecular characterization of an ecdysteroid inducible carboxylesterase with GQSCG motif in the corn borer, Sesamia nonagrioides

We obtained a full-length cDNA encoding a carboxylesterase in Sesamia nonagrioides. The complete cDNA sequence is comprised of 1838 bp with an open reading frame encoding 576 amino acid residues with predicted molecular mass of 64.24 kDa. The deduced amino acid sequence showed high identity to JHE-Related of Trichoplusia ni (65% amino acid identity) and 49-46% amino acid identity to JHEs of other lepidopterans and contained all five functional motifs of insect JHEs. The gene has been termed as SnJHE-Related (SnJHER) to denote its similarity to other insect JHE genes and the occurrence of an unusual cysteine residue immediately adjacent to the catalytic serine, instead of the conventional alanine residue. Phylogenetic analyses localised SnJHER together with TnJHER in a branch of the lepidopteran's JHEs group, with other carboxylesterases (COEs) occuring in separated groups. The JH analog methoprene did not affect the expression of SnJHER in contrast to other insect JHEs. Additionally, ecdysteroid analogs induced SnJHER gene expression. The SnJHER mRNA levels were higher in long-day non-diapausing larvae than in short-day diapausing ones. In the fifth instar of non-diapausing and ninth instar of diapausing larvae, the SnJHER mRNAs reached higher expression levels on the days close to each larval molt. In the last (sixth) non-diapausing larval instar, SnJHER mRNA levels peaked in the intermolt period but were lower than during the fifth instar.

FXPRL-amide peptides induce ecdysteroidogenesis through a G-protein coupled receptor expressed in the prothoracic gland of Bombyx mori

The FXPRL-amide peptide family (pyrokinin/PBAN family) consists of insect peptides that function broadly in insect life processes and are characterized by a conserved C-terminal motif. In the silkworm, Bombyx mori, sex pheromone biosynthesis and induction of embryonic diapause are regulated by peptides from this family. To elucidate other functions of Bombyx FXPRL-amide peptides, we analyzed the tissue expression patterns of two known Bombyx G-protein coupled receptors for these peptides. We found that the Bombyx diapause hormone receptor (BmDHR), is expressed in the prothoracic gland (PG), the organ which synthesizes and releases the insect molting hormones, ecdysteroids. Furthermore, diapause hormone (DH), a member of the Bombyx FXPRL-amide peptides, increases both intracellular Ca(2+) and cAMP concentrations and induces ecdysteroidogenesis in late fifth instar PGs coincident with BmDHR expression in the PGs. DH also has the highest prothoracicotropic activity among the FXPRL-amide peptides, which corresponds well to the ligand specificity of heterologously expressed BmDHR. These results demonstrate that FXPRL-amide peptides can function as prothoracicotropic factors through the activation of BmDHR and may play an important role in controlling molting and metamorphosis.

Identification of a novel prothoracicostatic hormone and its receptor in the silkworm Bombyx mori

The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis. Here we report the identification of a novel prothoracicostatic factor and its receptor in the silkworm Bombyx mori. The prothoracicostatic factor purified from pupal brains of B. mori is a decapeptide with the conserved structure of an insect myosuppressin and thus named Bommo-myosuppressin. Bommo-myosuppressin dose dependently suppressed the cAMP level and inhibited ecdysteroidogenesis in the larval prothoracic glands at much lower concentrations than the prothoracicostatic peptide, the other prothoracicostatic factor reported previously. In vitro analyses using a prothoracic gland incubation method revealed that Bommo-myosuppressin and prothoracicostatic peptide regulate the prothoracic gland activity via different receptors. In situ hybridization and immunohistochemistry revealed the existence of Bommo-myosuppressin in the brain neurosecretory cells projecting to neurohemal organs in which it is stored. We also identified and functionally characterized a specific receptor for Bommo-myosuppressin and showed its high expression in the prothoracic glands. All these results suggest that Bommo-myosuppressin functions as a prothoracicostatic hormone and plays an important role in controlling insect development.

Endocrine changes associated with metamorphosis and diapause induction in the yellow-spotted longicorn beetle, Psacothea hilaris

At 25 degrees C and under a long-day photoperiod, all 5th instar Psacothea hilaris larvae pupate at the next molt. Under a short-day photoperiod, in contrast, they undergo one or two additional larval molts and enter diapause; the 7th instar larvae enter diapause without further molt. The changes in hemolymph juvenile hormone (JH III) titers, JH esterase activity, and ecdysteroid titers in pupation-destined, pre-diapause, and diapause-destined larvae were examined. JH titers of the 5th instar pupation-destined larvae decreased continuously from 1.3 ng/ml and became virtually undetectable on day 13, when JH esterase activity peaked. Ecdysteroids exhibited a small peak on day 8, 1 day before gut purge, and a large peak on day 11, 2 days before the larvae became pre-pupae. The two ecdysteroid peaks are suggested to be associated with pupal commitment and pupation, respectively. JH titers of the 5th instar pre-diapause larvae were maintained at approximately 1.5 ng/ml for 5 days and then increased to form a peak (3.3 ng/ml) on day 11. JH esterase activity remained at a low level throughout. Ecdysteroid levels exhibited a large peak of 40 ng/ml on day 18, coincident with the larval molt to the 6th instar. JH titers of the 7th instar diapause-destined larvae peaked at 1.9 ng/ml on day 3, and a level of approximately 1.1 ng/ml was maintained even 30-60 days into the instar, when they were in diapause. Ecdysteroid titers remained approximately 0.02 ng/ml. Diapause induction in this species was suggested to be a consequence of high JH and low ecdysteroid titers.

Hormonal regulation and functional role of Drosophila E75A orphan nuclear receptor in the juvenile hormone signaling pathway

Ecdysone and juvenile hormone (JH) are important regulators of insect growth and development. While ecdysone initiates a transition from one developmental stage to another, JH determines the nature of the transition. How these two hormones interact at the molecular level is not known. Here we report the JH inducibility of the E75A nuclear receptor encoded by the E75 early ecdysone-inducible gene. In Drosophila S2 cells, E75A transcription is specifically activated by JH at concentrations well within the physiological range found in larvae and adults. The induction is rapid and does not require a concurrent protein synthesis, and thus represents a primary hormone response. Consistent with JH regulation, E75A mRNA levels are reduced in ovaries of apterous(4) mutant adults defective in JH secretion. Expression is rescued by topical methoprene application. We further provide evidence that ectopic E75A is sufficient to perform several functions in the JH signaling pathway. First, it can down-regulate its own transcription. Second, E75A can potentiate the JH inducibility of a secondary response gene, JhI-21. Finally, in the presence of JH, E75A can repress ecdysone activation of early genes including Broad-Complex. Based on these data, we propose a model for the role of E75A in the ecdysone-JH regulatory interplay.

Effects of 20-hydroxyecdysone and serotonin on neurite growth and survival rate of antennal lobe neurons in pupal stage of the silk moth Bombyx mori in vitro

Effects of 20-hydroxyecdysone and serotonin on the morphological development and the survival of antennal lobe neurons from day-2 pupal brains of the silk moth Bombyx mori were investigated in vitro. Four morphologically distinct neuronal types could be identified in the cultured antennal lobe neurons: unipolar, bipolar, multi-polar and projection neurons. Antennal lobe neurons in culture with 20-hydroxyecdysone and serotonin showed different patterns of the morphological development from those described in Manduca sexta. Projection neurons extend their neurites remarkably by 20-hydroxyecdysone in B. mori, but there is no extension from antennal lobe neurons in M. sexta. Multi-polar neurons conspicuously increase only formation of new branches from their primary neurites by serotonin in B. mori, but there are both extension and branching of the neurites in M. sexta. On day-5, antennal lobe neurons in lower titers of 20-hydroxyecdysone had significantly higher survival rates than those in higher titers. Neurons cultured for 7 days at different levels of 20-hydroxyecdysone generally showed significantly lower survival rates than neurons cultured for 5 days under the same conditions.

Induction of dauer pupae by fenoxycarb in the silkworm, Bombyx mori

Topical application of fenoxycarb (1 &mgr;g per animal) at 129 or 132 h of the fifth instar larvae of the silkworm, Bombyx mori, did not induce morphological abnormalities in the pupal stage, but these animals became dauer (permanent) pupae. This condition of B. mori and the endocrine events leading to permanent pupae are discussed in this work. Application of fenoxycarb at 132 h of the fifth instar elicited a high ecdysteroid titre in the pharate pupal stage and a steadily high ecdysteroid titre in the pupal stage. The fenoxycarb-induced permanent pupae had non-degenerating prothoracic glands that secreted low amounts of ecdysteroid and did not respond to recombinant prothoracicotropic hormone (rPTTH) late in the pupal stage. The Bombyx PTTH titre in the haemolymph, determined by a time-resolved fluoroimmunoassay, was lower than that of controls at the time of pupal ecdysis, but higher than controls later in the pupal stage in fenoxycarb-treated animals. After application of fenoxycarb, its haemolymph level, measured by ELISA, reached a peak at pupal ecdysis, then remained low. These results suggest that the fenoxycarb-mediated induction of permanent pupae is only partially a brain-centred phenomenon. It also involves alterations in the hormonal interplay that govern both the initiation of pupal-adult differentiation and changes in the steroidogenic pathway of the prothoracic glands of B. mori.

Basic pattern of fluctuation in hemolymph PTTH titers during larval-pupal and pupal-adult development of the silkworm, Bombyx mori

General features of the changes in hemolymph PTTH titers during larval-pupal and pupal-adult development of the silkworm Bombyx mori were analyzed by comparing the patterns of the titer changes between different races and between silkworms reared under different environmental conditions. In common to all types of the silkworms tested, we observed low PTTH titers during the phagoperiod of the final instar, a small rise in PTTH titer on the day before wandering, two middle-sized peaks of the titer at the wandering and prepupal stages, high PTTH titers during early pupal-adult development, and a gradual titer increase shortly before adult eclosion. Increases in hemolymph PTTH titer were closely correlated with increases in ecdysteroid titers and with subsequent occurrences of morphological and behavioral changes characteristic of the initiation or progression of metamorphosis. The timing of the increase in hemolymph PTTH titer on the day of wandering was photoperiodically controlled, but that timing at the later stages seemed not to be influenced by the light-dark cycle.