Juvenile Hormone Levels Research Articles

Effect and Mechanism of Uric Acid in Regulating Larval Growth and Development of Drosophila Melanogaster

Objective To explore the effect and mechanism of uric acid (UA) in regulating the larval growth and development of Drosophila melanogaster. Methods A total of 1350 newly hatched first-instar larvae of wild-type Drosophila melanogaster (W1118) were collected,and the Drosophila melanogaster model of hyperuricemia was constructed with a high purine diet.The larvae were assigned into three groups (n=150):control (standard corn meal medium),low-dose adenine (corn meal medium containing 0.05% adenine),and high-dose adenine (corn meal medium containing 0.10% adenine),and two parallel groups were set up.The growth and development of larvae in each group was observed,and the UA and hormone levels were measured.In addition,the expression levels of genes involved in growth and development were determined. Results Compared with the control group,the low- and high-dose adenine groups showed elevated UA levels (both P<0.001) and prolonged developmental period (P=0.024,P<0.001).The high-dose adenine group showed decreased survival rate,pupation rate,and eclosion rate and elevated levels of juvenile hormone (JH) and 20-hydroxyecdysone (20E) (all P<0.001).The PCR results showed that compared with the control group,high-dose adenine upregulated the mRNA levels of reactive oxygen species (ROS),forkhead box O (FOXO),and mammalian target of rapamycin (mTOR) while downregulating the mRNA levels of Sestrin,mTOR complex 1(mTORC1),and AMP-activated protein kinase (all P<0.001). Conclusion High concentrations of UA may promote the expression of ROS/FOXO/mTORC1/mTOR signaling pathway by regulating the levels of JH and 20E,thereby inhibiting the larval growth and development of Drosophila melanogaster.

The miRNA-mRNA modules enhance juvenile hormone biosynthesis for insect vitellogenesis and egg production.

In addition to preventing precocious larval metamorphosis, juvenile hormone (JH), synthesized in corpora allata (CA), is known to stimulate female reproduction of insects. JH titer is extremely low or absent during metamorphosis, but thereafter rapidly increases in the previtellogenic stage and rises to a peak in the vitellogenic phase. However, the mechanisms underlying the biosynthesis of high levels of JH in adults remain unclear. We found in this study that 12 genes involved in JH synthesis pathway were highly expressed in the CA of adult locusts. By transcriptome analysis and quantitative real-time - polymerase chain reaction validation, a total of 106 evolutionary conserved micro RNAs (miRNAs) and 163 species-specific miRNAs were identified in locust CA. Dual-luciferase assay revealed that 17 miRNAs bound to 10 JH synthesis genes (JHSGs) and downregulated their expression. These miRNAs were expressed in low levels during vitellogenic stage, which was oppositive from that of targeting JHSGs. Six miRNAs including miR-971-3p, miR-31a, miR-9-5p, miR-1-3p, miR-315, and miR-282 were selected for function study. Co-application of agomiRs resulted in significantly decreased levels of targeting JHSGs, accompanied by significantly reduced vitellogenin expression as well as arrested ovarian development. The data suggest that multiple miRNAs expressed synchronously at low levels in the vitellogenic phase, thereby ensuring the high levels of JHSG expression to facilitate JH biosynthesis required for JH-dependent female reproduction. The findings provide important information for deciphering miRNA-messenger RNA modules for JH biosynthesis as well as JH regulation of insect metamorphosis and reproduction.

Transcriptome and Metabolome Analysis of BmFAMeT6 Overexpression in Bombyx mori.

Background/Objectives: The gene-encoding farnesyl diphosphate O-methyltransferase 6 (FAMeT 6) is a member of the farnesyl diphosphate O-methyltransferase family. Our previous studies have demonstrated its influence on juvenile hormone levels in third instar silkworm larvae. Methods: we utilized transcriptomic and metabolomic techniques to investigate the changes in third instar larvae at 0, 12, and 24 h following BmFAMeT6 overexpression. Results: (1) The differentially expressed homologous genes were enriched in detoxification-related pathways at all three time points. (2) Transcription factor analysis of DEGs indicated a predominant presence of ZF-C2H2. (3) The metabolite-related network suggested that BmFAMeT6 may influence the metabolism of silkworm larvae through the ABC transporters, purine metabolism, and tyrosine metabolism pathways. (4) The differential gene count, differential metabolite count, and types of metabolites at the three time points indicated a shift in the regulatory focus within the larvae as time progresses, with the inflection point of regulation occurring at the third instar larval stage, 12 h. Conclusion: In summary, our research indicates that the regulatory role of BmFAMeT6 occurs within the context of the domestic silkworm's own growth and development regulation.

Knockdown of TcGluCl leads to the premature pupation of Tribolium castaneum larvae possibly by influencing the calcium-mediating hormone homeostasis

The glutamate-gated chloride channels (GluCls) are widely existed in the neural and nonneural tissues of invertebrate. In addition to play important roles in signal transduction, the GluCls also showed multiple physiological functions in insects such as participate in the juvenile hormone synthesis. In the present study, the potential roles of TcGluCl in growth and development of the red flour beetle Tribolium castaneum were explored. Knockdown of TcGluCl showed no effects on the survivability, weight growth, final pupation rate, eclosion and fecundity of T. castaneum, whereas resulted in the significant premature pupation of larvae. Inhibition of TcGluCl expression significantly changed the levels of juvenile hormone and ecdysone as well as the expressions of hormone biosynthetic genes. The increased ecdysone level and decreased juvenile hormone level were observed at the late stage of dsGluCl-treated larvae. Knockdown of TcGluCl significantly reduced the expressions of TcSTIM1 and TcOrai1, which were the primary proteins in store-operated calcium entry (SOCE) mediated Ca2+ influx mechanism. Whilst the L-glutamic acid treatment led to the increased TcOrai1 expression in T. castaneum. These findings suggested that knockdown of TcGluCl increased the ecdysone level and contributed to the premature pupation of larvae, which might be due to the reduced Ca2+ influx caused by the decreased expressions of TcSTIM1 and TcOrai1. These studies provide novel insights on the function of GluCls in insects.

Artificial diets can manipulate the reproductive development status of predatory ladybird beetles and hold promise for their shelf-life management

With the development of biological control methods, the predatory ladybird beetle Harmonia axyridis Pallas (Coleoptera: Coccinellidae) has been widely used for pest control in agricultural production. Appropriate shelf-life management strategies could synchronize H. axyridis production with pest outbreaks, finally improving the effectiveness of biological control. Herein, we preliminarily explored whether an artificial diet could optimize the shelf-life management of H. axyridis. We compared the survival rate, nutrition accumulation, reproductive development, juvenile hormone (JH) related-gene expression levels, and stress resistance gene expression levels between aphid-fed and artificial diet-fed H. axyridis females. The results revealed that H. axyridis females maintained a high survival rate after being fed an artificial diet for 60 days, whereas the survival rate of aphid-fed females decreased. Continuous feeding of the artificial diet caused H. axyridis females to enter a diapause-like state, which was characterized by low JH levels, high triglycerides and trehalose accumulation, ovarian development inhibition, decreased Vgs expression levels, and increased stress resistance gene expression levels. This diapause-like state could be promptly recovered upon transferring to an aphid diet. These results indicate that the artificial diet could manipulate the reproductive development status of H. axyridis and lay the foundation for its shelf-life management.

Fertility differences between two wild-type Drosophila melanogaster lines correlate with differences in the expression of the Jheh1 gene, which codes for an enzyme degrading juvenile hormone.

Juvenile hormone plays a "status quo" role in Drosophila melanogaster larvae, preventing the untimely metamorphosis, and performs a gonadotropic function in imagoes, ensuring the ovaries' preparedness for vitellogenesis. The decreased level of juvenile hormone results in reproductive disorders in D. melanogaster females including a delay in the oviposition onset and a fertility decrease. Another factor that can affect the insect reproduction is an infection with the maternally inherited symbiotic α-proteobacterium Wolbachia. The present study is devoted to the analysis of the expression of two juvenile hormone metabolism genes encoding enzymes of its synthesis and degradation, juvenile hormone acid O-methyltransferase ( jhamt) and juvenile hormone epoxide hydrase (Jheh1), respectively, in four wild-type D. melanogaster lines, two of them being infected with Wolbachia. Lines w153 and Bi90 were both derived from an individual wild-caught females infected with Wolbachia, while lines w153T and Bi90T were derived from them by tetracycline treatment and are free of infection. Line Bi90 is known to be infected with the Wolbachia strain wMel, and line w153, with the Wolbachia strain wMelPlus belonging to the wMelCS genotype. It was found that infection with either Wolbachia strain does not affect the expression of the studied genes. At the same time, it was shown that the w153 and w153T lines differ from the Bi90 and Bi90T lines by an increased level of the Jheh1 gene expression and do not differ in the jhamt gene expression level. Analysis of the fertility of these four lines showed that it does not depend on Wolbachia infection either, but differs between lines with different nuclear genotypes: in w153 and w153T, it is significantly lower than in lines Bi90 and Bi90T. The data obtained allow us to reasonably propose that the inter-line D. melanogaster polymorphism in the metabolism of the juvenile hormone is determined by its degradation (not by its synthesis) and correlates with the fertility level.

The embryonic role of juvenile hormone in the firebrat, Thermobia domestica, reveals its function before its involvement in metamorphosis.

To gain insights into how juvenile hormone (JH) came to regulate insect metamorphosis, we studied its function in the ametabolous firebrat, Thermobia domestica. Highest levels of JH occur during late embryogenesis, with only low levels thereafter. Loss-of-function and gain-of-function experiments show that JH acts on embryonic tissues to suppress morphogenesis and cell determination and to promote their terminal differentiation. Similar embryonic actions of JH on hemimetabolous insects with short germ band embryos indicate that JH's embryonic role preceded its derived function as the postembryonic regulator of metamorphosis. The postembryonic expansion of JH function likely followed the evolution of flight. Archaic flying insects were considered to lack metamorphosis because tiny, movable wings were evident on the thoraces of young juveniles and their positive allometric growth eventually allowed them to support flight in late juveniles. Like in Thermobia, we assume that these juveniles lacked JH. However, a postembryonic reappearance of JH during wing morphogenesis in the young juvenile likely redirected wing development to make a wing pad rather than a wing. Maintenance of JH then allowed wing pad growth and its disappearance in the mature juvenile then allowed wing differentiation. Subsequent modification of JH action for hemi- and holometabolous lifestyles are discussed.

The Role of Cholesterol during the Ovarian Maturation and Lipid Metabolism of Female Chinese Mitten Crab (Eriocheir sinensis)

In previous study, we found that the cholesterol requirement of Eriocheir sinensis was 0.27%, to further investigate the effects of cholesterol on health status, ovarian maturation, and lipid metabolism of female Eriocheir sinensis broodstock. Two diets containing 0% and 0.25% (actually 0.05% and 0.27%) cholesterol were fed to the female crabs (average weight: 49.21 ± 0.11 g) for 4 months and sampled once a month. The results showed that the body weight (BW), survival rate (SR), meat yield (MY), condition factor (CF), hepatosomatic index (HSI), and gonadosomatic index (GSI) of Eriocheir sinensis were significantly affected by treatment time and compared with the cholesterol deficient group, supplementing cholesterol significantly increased BW, HSI, and GSI (P&lt;0.05). In addition, long-term lack of cholesterol will lead to a significant decrease in the activity of ACP, AKP, and SOD and a significant increase in the content of MDA. The histological results showed that cholesterol significantly increased the volume of oocytes (P&lt;0.05). Further studies found that 0.27% cholesterol significantly increased the transcription levels of vtg and vgr in hepatopancreas and ovaries, which may be the main reason for the increase of oocyte size (P&lt;0.05). When fed with 0.27% cholesterol diet, the contents of nutrients in hepatopancreas and ovaries increased significantly, especially lipids and cholesterol (P&lt;0.05). Through the analysis of mRNA expression level of genes related to lipid metabolism, it was found that cholesterol enhanced the transcription level of genes related to lipid synthesis and transport in hepatopancreas, thereby promoting the accumulation of lipid in the organism. Furthermore, compared with control group, the levels of juvenile hormone (JH), 17β-estradiol (E2), methyl farnesoate (MF), and ecdysone in the organism were significantly increased after feeding a diet with 0.27% cholesterol (P&lt;0.05). In summary, supplementing an appropriate amount of cholesterol in the diet can improve the growth performance of Eriocheir sinensis broodstock, enhance the body’s antioxidant and immune system, and promote the accumulation of nutrients in the ovaries, thereby promoting ovarian maturation.

TGFß/activin-dependent activation of Torso controls the timing of the metamorphic transition in the red flour beetle Tribolium castaneum.

Understanding the mechanisms governing body size attainment during animal development is of paramount importance in biology. In insects, a crucial phase in determining body size occurs at the larva-pupa transition, marking the end of the larval growth period. Central to this process is the attainment of the threshold size (TS), a critical developmental checkpoint that must be reached before the larva can undergo metamorphosis. However, the intricate molecular mechanisms by which the TS orchestrates this transition remain poor understood. In this study, we investigate the role of the interaction between the Torso and TGFß/activin signaling pathways in regulating metamorphic timing in the red flour beetle, Tribolium castaneum. Our results show that Torso signaling is required specifically during the last larval instar and that its activation is mediated not only by the prothoracicotropic hormone (Tc-Ptth) but also by Trunk (Tc-Trk), another ligand of the Tc-Torso receptor. Interestingly, we show that while Tc-Torso activation by Tc-Ptth determines the onset of metamorphosis, Tc-Trk promotes growth during the last larval stage. In addition, we found that the expression of Tc-torso correlates with the attainment of the TS and the decay of juvenile hormone (JH) levels, at the onset of the last larval instar. Notably, our data reveal that activation of TGFß/activin signaling pathway at the TS is responsible for repressing the JH synthesis and inducing Tc-torso expression, initiating metamorphosis. Altogether, these findings shed light on the pivotal involvement of the Ptth/Trunk/Torso and TGFß/activin signaling pathways as critical regulatory components orchestrating the TS-driven metamorphic initiation, offering valuable insights into the mechanisms underlying body size determination in insects.

Investigating the role of aae-miR-34-5p in the regulation of juvenile hormone biosynthesis genes in the mosquito Aedes aegypti

Juvenile hormone (JH) controls the development and reproduction of insects. Therefore, a tight regulation of the expression of JH biosynthetic enzymes is critical. microRNAs (miRNAs) play significant roles in the post-transcriptional regulation of gene expression by interacting with complementary sequences in target genes. Previously, we reported that several miRNAs were differentially expressed during three developmental stages of Aedes aegypti mosquitoes with different JH levels (no JH, high JH, and low JH). One of these miRNAs was aae-miR-34-5p. In this study, we identified the presence of potential target sequences of aae-miR-34-5p in the transcripts of some genes encoding JH biosynthetic enzymes. We analysed the developmental expression patterns of aae-miR-34-5p and the predicted target genes involved in JH biogenesis. Increases in miRNA abundance were followed, with a delay, by decreases in transcript levels of target genes. Application of an inhibitor and a mimic of aae-miR-34-5p led respectively to increased and decreased levels of thiolase transcripts, which is one of the early genes of JH biosynthesis. Female adult mosquitoes injected with an aae-miR-34-5p inhibitor exhibited significantly increased transcript levels of three genes encoding JH biosynthetic enzymes, acetoacetyl-CoA thiolase (thiolase), farnesyl diphosphate phosphatase, and farnesal dehydrogenase. Overall, our results suggest a potential role of miRNAs in JH production by directly targeting genes involved in its biosynthesis.

Feeding Spodoptera exigua larvae with gut-derived Escherichia sp. increases larval juvenile hormone levels inhibiting cannibalism

Feed quality influences insect cannibalistic behavior and gut microbial communities. In the present study, Spodoptera exigua larvae were fed six different artificial diets, and one of these diets (Diet 3) delayed larval cannibalistic behavior and reduced the cannibalism ratio after ingestion. Diet 3-fed larvae had the highest gut bacterial load (1.396 ± 0.556 × 1014 bacteria/mg gut), whereas Diet 2-fed larvae had the lowest gut bacterial load (3.076 ± 1.368 × 1012 bacteria/mg gut). The gut bacterial composition and diversity of different diet-fed S. exigua larvae varied according to the 16S rRNA gene sequence analysis. Enterobacteriaceae was specific to the Diet 3-fed larval gut. Fifteen culturable bacterial isolates were obtained from the midgut of Diet 3-fed larvae. Of these, ten belonged to Escherichia sp. After administration with Diet 1- or 2-fed S. exigua larvae, two bacterial isolates (SePC-12 and -37) delayed cannibalistic behavior in both tested larval groups. Diet 2-fed larvae had the lowest Juvenile hormone (JH) concentration and were more aggressive against intraspecific predation. However, SePC-12 loading increased the JH hormone levels in Diet 2-fed larvae and inhibited their cannibalism. Bacteria in the larval midgut are involved in the stabilization of JH levels, thereby regulating host larval cannibalistic behavior.

Hormonal gatekeeping via the blood-brain barrier governs caste-specific behavior in ants

Here, we reveal an unanticipated role of the blood-brain barrier (BBB) in regulating complex social behavior in ants. Using scRNA-seq, we find localization in the BBB of a key hormone-degrading enzyme called juvenile hormone esterase (Jhe), and we show that this localization governs the level of juvenile hormone (JH3) entering the brain. Manipulation of the Jhe level reprograms the brain transcriptome between ant castes. Although ant Jhe is retained and functions intracellularly within the BBB, we show that Drosophila Jhe is naturally extracellular. Heterologous expression of ant Jhe into the Drosophila BBB alters behavior in fly to mimic what is seen in ants. Most strikingly, manipulation of Jhe levels in ants reprograms complex behavior between worker castes. Our study thus uncovers a remarkable, potentially conserved role of the BBB serving as a molecular gatekeeper for a neurohormonal pathway that regulates social behavior.

Exorista sorbillans (Diptera: Tachinidae) parasitism shortens host larvae growth duration by regulating ecdysone and juvenile hormone titers in Bombyx mori (Lepidoptera: Bombycidae).

The tachinid fly, Exorista sorbillans, is a notorious ovolarviparous endoparasitoid of the silkworm, Bombyx mori, causing severe damage to silkworm cocoon industry. Silkworm larvae show typically precocious wandering behavior after being parasitized by E. sorbillans; however, the underlying molecular mechanism remains unexplored. Herein, we investigated the changes in the levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) titer, and they both increased in the hemolymph of parasitized silkworms. Furthermore, we verified the expression patterns of related genes, which showed an upregulation of 20E signaling and biosynthesis genes but a significant downregulation of ecdysone oxidase (EO), a 20E inactivation enzyme, in parasitized silkworms. In addition, related genes of the JH signaling were activated in parasitized silkworms, while related genes of the JH degradation pathway were suppressed, resulting in an increase in JH titer. Notably, the precocious wandering behavior of parasitized silkworms was partly recoverable by silencing the transcriptions of BmCYP302A1 or BmCYP307A1 genes. Our findings suggest that the developmental duration of silkworm post parasitism could be shortened by regulation of 20E and JH titers, which may help silkworm to resist the E. sorbillans infestation. These findings provide a basis for deeper insight into the interplay between silkworms and E. sorbillans and may serve as a reference for the development of a novel approach to control silkworm myiasis.

Convergent and complementary selection shaped gains and losses of eusociality in sweat bees.

Sweat bees have repeatedly gained and lost eusociality, a transition from individual to group reproduction. Here we generate chromosome-length genome assemblies for 17 species and identify genomic signatures of evolutionary trade-offs associated with transitions between social and solitary living. Both young genes and regulatory regions show enrichment for these molecular patterns. We also identify loci that show evidence of complementary signals of positive and relaxed selection linked specifically to the convergent gains and losses of eusociality in sweat bees. This includes two pleiotropic proteins that bind and transport juvenile hormone (JH)-a key regulator of insect development and reproduction. We find that one of these proteins is primarily expressed in subperineurial glial cells that form the insect blood-brain barrier and that brain levels of JH vary by sociality. Our findings are consistent with a role of JH in modulating social behaviour and suggest that eusocial evolution was facilitated by alteration of the proteins that bind and transport JH, revealing how an ancestral developmental hormone may have been co-opted during one of life's major transitions. More broadly, our results highlight how evolutionary trade-offs have structured the molecular basis of eusociality in these bees and demonstrate how both directional selection and release from constraint can shape trait evolution.

The role of Wolbachia and the environment on sex determination of the Indian lac insect, Kerria lacca (Coccoidea: Tachardiidae)

• In Kerria lacca , presence of endosymbiont Wolbachia is developmental-stage dependent. • Administration of antibiotic enhances the sex ratio of the lac insect multifold. • The lac insect sex ratio is influenced by environmental factors. • Mode of metamorphosis together with Wolbachia dynamics explains sex ratio changes. The Indian lac insect, Kerria lacca (Kerr) exhibits a highly variable sex ratio, apparently influenced by various environmental factors, in the absence of a chromosomal sex determination mechanism. The endosymbiont Wolbachia, well known as sex ratio distorter, was reported in this species but its role in the sex determination of the host has hitherto remained unexplored. Distinct variation in the presence of Wolbachia was observed in relation to the developmental stages and the sexes of K. lacca as well as the host plant species; adult males of W + whereas adult females are W -. The post-settlement environmental factors such as host plant, season and genetic makeup affect the sex ratio in this insect, probably mediated through Wolbachia dynamics. Denser settlement of the crawlers led to comparatively higher Wolbachia presence with an elevated sex ratio. Suppression of Wolbachia through antibiotic administration resulted in a nearly three-fold increase in the sex ratio. Distinct transitions in the proportion of insects with heterochromatic genome (cytological males) have been observed during the first instar on different host plants, indicating that changes in the sex ratio occur during early development phase. Environmental factors appear to influence Wolbachia , which in turn brings about sex ratio changes, probably mediated through changes in juvenile hormone levels, as the male and female lac insects show distinct modes of metamorphosis.

Crosstalk between Nutrition, Insulin, Juvenile Hormone, and Ecdysteroid Signaling in the Classical Insect Model, Rhodnius prolixus

The rigorous balance of endocrine signals that control insect reproductive physiology is crucial for the success of egg production. Rhodnius prolixus, a blood-feeding insect and main vector of Chagas disease, has been used over the last century as a model to unravel aspects of insect metabolism and physiology. Our recent work has shown that nutrition, insulin signaling, and two main types of insect lipophilic hormones, juvenile hormone (JH) and ecdysteroids, are essential for successful reproduction in R. prolixus; however, the interplay behind these endocrine signals has not been established. We used a combination of hormone treatments, gene expression analyses, hormone measurements, and ex vivo experiments using the corpus allatum or the ovary, to investigate how the interaction of these endocrine signals might define the hormone environment for egg production. The results show that after a blood meal, circulating JH levels increase, a process mainly driven through insulin and allatoregulatory neuropeptides. In turn, JH feeds back to provide some control over its own biosynthesis by regulating the expression of critical biosynthetic enzymes in the corpus allatum. Interestingly, insulin also stimulates the synthesis and release of ecdysteroids from the ovary. This study highlights the complex network of endocrine signals that, together, coordinate a successful reproductive cycle.

A possible mechanism of Cry7Ab4 protein in delaying pupation of Plutella xylostella larvae.

Cry toxins produced by Bacillus thuringiensis (Bt) are well known for their insecticidal activities against Lepidopteran, Dipteran, and Coleopteran species. In our previous work, we showed that trypsin-digested full-length Cry7Ab4 protoxin did not have insecticidal activity against Plutella xylostella larvae but strongly inhibited their growth. In this paper, we expressed and purified recombinant active Cry7Ab4 toxic core from Escherichia coli for bioassay and identified its binding proteins. Interestingly, Cry7Ab4 toxic core exhibited activity to delay the pupation of P. xylostella larvae. Using protein pull-down assay, several proteins, including basic juvenile hormone-suppressible protein 1-like (BJSP-1), were identified from the midgut juice of P. xylostella larvae as putative Cry7Ab4-binding proteins. We showed that feeding P. xylostella larval Cry7Ab4 toxic core upregulated the level of BJSP-1 mRNA in the hemocytes and fat body and decreased the free juvenile hormone (JH) level in larvae. BJSP-1 interacted with Cry7Ab4 and bound to free JH in vitro. A possible mechanism of Cry7Ab4 in delaying the pupation of P. xylostella larvae was proposed.

Conceptual framework for the insect metamorphosis from larvae to pupae by transcriptomic profiling, a case study of Helicoverpa armigera (Lepidoptera: Noctuidae)

BackgroundInsect metamorphosis from larvae to pupae is one of the most important stages of insect life history. Relatively comprehensive information related to gene transcription profiles during lepidopteran metamorphosis is required to understand the molecular mechanism underlying this important stage. We conducted transcriptional profiling of the brain and fat body of the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) during its transition from last instar larva into pupa to explore the physiological processes associated with different phases of metamorphosis.ResultsDuring metamorphosis, the differences in gene expression patterns and the number of differentially expressed genes in the fat body were found to be greater than those in the brain. Each stage had a specific gene expression pattern, which contributed to different physiological changes. A decrease in juvenile hormone levels at the feeding stage is associated with increased expression levels of two genes (juvenile hormone esterase, juvenile hormone epoxide hydrolase). The expression levels of neuropeptides were highly expressed at the feeding stage and the initiation of the wandering stage and less expressed at the prepupal stage and the initiation of the pupal stage. The transcription levels of many hormone (or neuropeptide) receptors were specifically increased at the initiation of the wandering stage in comparison with other stages. The expression levels of many autophagy-related genes in the fat body were found to be gradually upregulated during metamorphosis. The activation of apoptosis was probably related to enhanced expression of many key genes (Apaf1, IAP-binding motif 1 like, cathepsins, caspases). Active proliferation might be associated with enhanced expression levels in several factors (JNK pathway: jun-D; TGF-β pathway: decapentaplegic, glass bottom boat; insulin pathway: insulin-like peptides from the fat body; Wnt pathway: wntless, TCF/Pangolin).ConclusionsThis study revealed several vital physiological processes and molecular events of metamorphosis and provided valuable information for illustrating the process of insect metamorphosis from larvae to pupae.

Biological and physiological responses of Bradysia odoriphaga 4th instar larvae to long‐term mild heat stress

AbstractThe high summer temperature is a key barrier to Bradysia odoriphaga (Diptera: Sciaridae), a devastating soil pest in China. The 4th instar larvae possess the strongest thermal tolerance to high temperatures. To determine whether B. odoriphaga 4th instar larvae possessed other adaptations to summer mild heat stress than thermal plasticity, we evaluated the biological performance of 4th instar larvae under constant long‐term mild heat stress. The physiological responses were studied including energy storage, hormone level and related gene expression. Bioassay results indicated that 4th instar larvae survived, without pupation, for more than 40 days under long‐term mild heat stress (34°C). Long‐term mild heat stress pretreatment delayed larval development, reduced longevity and fecundity. A summer diapause‐like phenomenon was observed, including larval development stasis under mild heat exposure and prolonged recovery time after mild heat. Protective physiological responses were involved in regulating the larval stage, including fat and glycogen accumulation, a high level of juvenile hormone and a low level of moulting hormone. In addition, high expression levels of hsp70 and hsp90 were detected. The delayed development of 4th instar larvae appears to be a special adaptation strategy to withstand mild heat stress in summer that regulated by complex physiological processes.

Caterpillar-Induced Rice Volatile (E)-β-Farnesene Impairs the Development and Survival of Chilo suppressalis Larvae by Disrupting Insect Hormone Balance.

Significant research progress has recently been made on establishing the roles of tps46 in rice defense. (E)-β-farnesene (Eβf) is a major product of tps46 activity but its physiological functions and potential mechanisms against Chilo suppressalis have not yet been clarified. In the present study, C. suppressalis larvae were artificially fed a diet containing 0.8 g/kg Eβf and the physiological performance of the larvae was evaluated. In response to Eβf treatment, the average 2nd instar duration significantly increased from 4.78 d to 6.31 d while that of the 3rd instar significantly increased from 5.70 d to 8.00 d compared with the control. There were no significant differences between the control and Eβf-fed 4th and 5th instars in terms of their durations. The mortalities of the 2nd and 3rd Eβf-fed instars were 21.00-fold and 6.39-fold higher, respectively, than that of the control. A comparative transcriptome analysis revealed that multiple differentially expressed genes are involved in insect hormone biosynthesis. An insect hormone assay on the 3rd instars disclosed that Eβf disrupted the balance between the juvenile hormone and ecdysteroid levels. Eβf treatment increased the juvenile hormones titers but not those of the ecdysteroids. The qPCR results were consistent with those of the RNA-Seq. The foregoing findings suggested that Eβf impairs development and survival in C. suppressalis larvae by disrupting their hormone balance. Moreover, Eβf altered the pathways associated with carbohydrate and xenobiotic metabolism as well as those related to cofactors and vitamins in C. suppressalis larvae. The discoveries of this study may contribute to the development and implementation of an integrated control system for C. suppressalis infestations in rice.