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The article discusses a posthumanist reading of Edgar Allan Poe's novella, "The Narrative of Arthur Gordon Pym of Nantucket," focusing on the role of the dog in the story. Scholars have traditionally overlooked the nonhuman animals in the novel, particularly the dog, which plays a significant role in influencing the protagonist and advancing the narrative. The article argues for considering the dog's animal agency and the underlying posthumanist implications in Poe's story, challenging traditional human-centered worldviews and emphasizing the significance of non-human entities. The dog's agency is highlighted through its disobedience, disappearance, and resistance to human re-plotting, symbolizing the persistence of animal agency and challenging the centrality of human beings. [Extracted from the article]

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. [ABSTRACT FROM AUTHOR]

More than 50% of all animal species are insects that undergo complete metamorphosis. The key innovation of these holometabolous insects is a pupal stage between the larva and adult when most structures are completely rebuilt. Why this extreme lifestyle evolved is unclear. Here, we test the hypothesis that a trade-off between growth and differentiation explains the evolution of this novelty. Using a comparative approach, we find that holometabolous insects grow much faster than hemimetabolous insects. Using a theoretical model, we then show how holometaboly evolves under a growth-differentiation trade-off and identify conditions under which such temporal decoupling of growth and differentiation is favored. Our work supports the notion that the holometabolous life history evolved to remove developmental constraints on fast growth, primarily under high mortality. [ABSTRACT FROM AUTHOR]

Blow flies (Diptera: Calliphoridae) are generally early colonisers of fresh cadavers, enabling the estimation of a minimum post-mortem interval (minPMI) based on an accurate aging of the oldest immature stages associated with a cadaver. In blow flies, the pupal stage and the subsequent development of the adult take place inside a protective case, the puparium, formed from the hardened and darkened cuticle of the third instar larva. Because the puparium is an opaque structure that shows virtually no external changes, qualitative analyses of the internal tissues can be very informative for determining reliable age-specific morphological markers. Those analyses can be performed using either non-invasive but expensive and not widely accessible techniques, or traditional histological methods, which are invasive as they require the serial sectioning of the sample. Histological methods are often readily available for forensic researchers and practitioners; however, the histological study of blow fly intra-puparial stages has traditionally been hampered by the poor paraffin infiltration of tissues due to the abundance of fat bodies, resulting in usually fragmented sections and the subsequent loss of relevant information. We present here an effective method for the preparation of histological sections of blow fly intra-puparial stages, maximising the paraffin infiltration while enabling the production of clean and entire sections that allow for the use of reliable age-specific morphological markers, thus improving the accuracy of minPMI estimations when access to more costly techniques is not feasible. [ABSTRACT FROM AUTHOR]

Background: Free fatty acids (FFAs) play vital roles as energy sources and substrates in organisms; however, the molecular mechanism regulating the homeostasis of FFA levels in various circumstances, such as feeding and nonfeeding stages, is not fully clarified. Holometabolous insects digest dietary triglycerides (TAGs) during larval feeding stages and degrade stored TAGs in the fat body during metamorphosis after feeding cessation, which presents a suitable model for this study. Results: This study reported that two lipases are differentially regulated by hormones to maintain the homeostasis of FFA levels during the feeding and nonfeeding stages using the lepidopteran insect cotton bollworm Helicoverpa armigera as a model. Lipase member H-A-like (Lha-like), related to human pancreatic lipase (PTL), was abundantly expressed in the midgut during the feeding stage, while the monoacylglycerol lipase ABHD12-like (Abhd12-like), related to human monoacylglycerol lipase (MGL), was abundantly expressed in the fat body during the nonfeeding stage. Lha-like was upregulated by juvenile hormone (JH) via the JH intracellular receptor methoprene-tolerant 1 (MET1), and Abhd12-like was upregulated by 20-hydroxyecdysone (20E) via forkhead box O (FOXO) transcription factor. Knockdown of Lha-like decreased FFA levels in the hemolymph and reduced TAG levels in the fat body. Moreover, lipid droplets (LDs) were small, the brain morphology was abnormal, the size of the brain was small, and the larvae showed the phenotype of delayed pupation, small pupae, and delayed tissue remodeling. Knockdown of Abhd12-like decreased FFA levels in the hemolymph; however, TAG levels increased in the fat body, and LDs remained large. The development of the brain was arrested at the larval stage, and the larvae showed a delayed pupation phenotype and delayed tissue remodeling. Conclusions: The differential regulation of lipases expression by different hormones determines FFAs homeostasis and different TAG levels in the fat body during the feeding larval growth and nonfeeding stages of metamorphosis in the insect. The homeostasis of FFAs supports insect growth, brain development, and metamorphosis. [ABSTRACT FROM AUTHOR]

The Hemiptera insects are the largest incomplete metamorphosis insect group in Insecta and play a vital role in ecosystems and biodiversity. Previous studies on the spatial distribution of Hemiptera insects mainly focused on a specific region and insect, this study explored the spatial distribution characteristics of Hemiptera insects in China (national scale), and further clarified the dominant factors affecting their spatial distribution. We used spatial autocorrelation analysis, hot spot analysis, and standard ellipse to investigate the spatial distribution characteristics of Hemiptera insects in China. Furthermore, we used geographic detectors to identify the main factors affecting their spatial distribution under China's six agricultural natural divisions and explore the influencing mechanism of dominant factors. The results show that: (i) The spatial differentiation characteristics of Hemiptera insects in China are significant, and their distribution has obvious spatial agglomeration. The Hu Huanyong Line is an important dividing line for the spatial distribution of Hemiptera insects in China. From the city scale, the HH type (high‐high cluster) is mainly distributed on both sides of the Hu Huanyong Line. (ii) The hot spots of Hemiptera insects are mainly distributed in southwest China, along the Qinling Mountains, the western side of the Wuyi Mountains, the Yinshan Mountains, the Liupanshan Mountains, the Xuefeng Mountains, the Nanling Mountains, and other mountainous areas. (iii) Under agricultural natural divisions, the influence of natural environmental factors on the spatial distribution of Hemiptera insects is obviously different. Temperature and precipitation are the dominant factors. Natural factors and socio‐economic factors have formed a positive reinforcement interaction mode on the spatial distribution of Hemiptera insects. These can provide the decision‐making basis for biodiversity conservation and efficient pest control. [ABSTRACT FROM AUTHOR]

Complete insect metamorphosis requires substantial metabolic and physiological adjustments. Although oxidative stress has been implicated in metamorphosis, details on redox metabolism during larva-to-pupa and pupa-to-adult remain scarce. This study explores redox metabolism during metamorphosis of a lepidopteran (Chlosyne lacinia), focusing on core metabolism, antioxidant systems and oxidative stress. The larva-to-pupa transition was characterized by increased lactate dehydrogenase and glutathione peroxidase (GPX) activities, coupled with depletion of reduced glutathione (GSH), high disulfide-to-total-glutathione ratio (GSSG/tGSH), and increased lipid peroxidation. As metamorphosis progressed, metabolic enzyme activities, citrate synthase and glucose 6-phosphate dehydrogenase increased, indicating heightened oxidative metabolism associated with adult development. Concurrently, GSH and GPX levels returned to larval levels and GSSG/tGSH reached its most reduced state right before adult emergence. Adult emergence was marked by a further increase in oxidative metabolism, accompanied by redox imbalance and enhanced antioxidant mechanisms. These findings highlight a fluctuation in redox balance throughout metamorphosis, with periods of oxidative eustress followed by compensatory antioxidant responses. This study is the first to identify concurrent changes in metabolism, antioxidants, redox balance and oxidative stress throughout metamorphosis. Our findings extend knowledge on redox metabolism adjustments and highlight redox adaptations and oxidative stress as natural components of complete insect metamorphosis. [ABSTRACT FROM AUTHOR]

BACKGROUND: Galeruca daurica has become a new pest on the Inner Mongolia grasslands since an abrupt outbreak in 2009 caused serious damage. As a pupa indicator during insect metamorphosis, the early response gene of the ecdysone signaling pathway, Broad‐Complex (Br‐C), plays a vital role in the growth and development of insects. MicroRNAs (miRNAs) are small non‐coding RNAs which mediate various biological activities, but it is unknown whether and how Br‐C is regulated by miRNAs. RESULTS: Temporal expression profiles revealed that miR‐285 and Br‐C basically displayed an opposite trend during larval–adult development, and Br‐C was sharply up‐regulated on the last day of final‐instar larvae while miR‐285 was significantly down‐regulated. Both dual‐luciferase reporter assay and miRNA–mRNA interaction assay indicated that miR‐285 interacts with the coding sequence of Br‐C and represses its expression. Not only overexpression but also downexpression of miR‐285 led to the failure of larval to pupal to adult metamorphosis. In addition, both overexpression of miR‐285 and silence of Br‐C inhibited the expression of Br‐C and other ecdysone signaling pathway genes, including E74, E75, ECR, FTZ‐F1, and HR3. On the contrary, suppressing miR‐285 obtained opposite results. Further experiments showed that 20‐hydroxyecdysone down‐regulated miR‐285 and up‐regulated Br‐C and above‐mentioned genes, whereas juvenile hormone alalogue (JHA) resulted in opposite effects. CONCLUSION: Our results reveal that miR‐285 is involved in mediating the metamorphosis in G. daurica by targeting Br‐C in the ecdysone signaling pathway. miR‐285 and its target Br‐C could be as a potential target for G. daurica management. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Molting and metamorphosis are important physiological processes in insects that are tightly controlled by ecdysone receptor (EcR) through the 20‐hydroxyecdysone (20E) signaling pathway. EcR is a steroid nuclear receptor (SR). Several FK506‐binding proteins (FKBPs) have been identified from the mammal SR complex, and are thought to be involved in the subcellular trafficking of SR. However, their roles in insects are poorly understood. To explore whether FKBPs are involved in insect molting or metamorphosis, we injected an FKBP inhibitor (FK506) into a lepidopteran insect, Spodoptera litura, and found that molting was inhibited in 61.11% of the larvae, and that the time for larvae to pupate was significantly extended. A total of 10 FKBP genes were identified from the genome of S. litura and were clustered into 2 distinct groups, according to their subcellular localization, with FKBP13 and FKBP14 belonging to the endoplasmic reticulum (ER) group and with the other members belonging to the cytoplasmic (Cy) group. All the CyFKBPs were significantly upregulated in the prepupal or pupal stages, with the opposite being observed for the ER group members. FK506 completely blocked the transfer of EcR to the nucleus under 20E induction, and significantly downregulated the transcriptional expression of many 20E signaling genes. A similar phenomenon was observed after RNA interference of 2 CyFKBPs (FKBP45 and FKBP12b), but not for FKBP13. Taken together, our data indicate that the cytoplasmic FKBPs, especially FKBP45 and FKBP12b, mediate the nuclear localization of EcR, thereby regulating the 20E signaling and ultimately affecting molting and metamorphosis in insects. [ABSTRACT FROM AUTHOR]

This article reads Anna Letitia Barbauld's affective encounter in 'The Caterpillar' (1825) in the light of her broader entomological writing for both adults and children. It investigates the recommendations for attention to the small and the particular in her didactic work alongside the narratives of insect subjectivity and insect metamorphosis in her occasional and lyric verse to assess the poet's contribution to an ecological mode of writing in this period. This uncovers a key tension in Barbauld's communication of insect worlds, reflected in the conclusion of 'The Caterpillar', where the affective encounter exposes the inescapable otherness of the human observer. [ABSTRACT FROM AUTHOR]

Insect metamorphosis involves significant changes in insect internal structure and is thus a critical focus of entomological research. Investigating the morphological transformation of internal structures is vital to understanding the origins of adult insect organs. Beetles are among the most species-rich groups in insects, but the development and transformation of their internal organs have yet to be systematically documented. In this study, we have acquired a comprehensive dataset that includes 27 detailed whole-body tomographic image sets of Harmonia axyridis, spanning from the prepupal to the pupal stages. Utilizing this data, we have created intricate 3D models of key internal organs, encompassing the brain, ventral nerve cord, digestive and excretion systems, as well as the body wall muscles. These data documented the transformation process of these critical organs and correlations between the origin of adult and larval organs and can be used to enhance the understanding of holometabolous adult organ genesis and offers a valuable reference model for investigating complete metamorphosis in insects. [ABSTRACT FROM AUTHOR]

Histone acetylation, a crucial epigenetic modification, is governed by histone acetyltransferases (HATs), that regulate many biological processes. Functions of HATs in insects are not well understood. We identified 27 HATs and determined their functions using RNA interference (RNAi) in the model insect, Tribolium castaneum. Among HATs studied, N-alpha-acetyltransferase 40 (NAA40) knockdown caused a severe phenotype of arrested larval development. The steroid hormone, ecdysone induced NAA40 expression through its receptor, EcR (ecdysone receptor). Interestingly, ecdysone-induced NAA40 regulates EcR expression. NAA40 acetylates histone H4 protein, associated with the promoters of ecdysone response genes: EcR, E74, E75, and HR3, and causes an increase in their expression. In the absence of ecdysone and NAA40, histone H4 methylation by arginine methyltransferase 1 (ART1) suppressed the above genes. However, elevated ecdysone levels at the end of the larval period induced NAA40, promoting histone H4 acetylation and increasing the expression of ecdysone response genes. NAA40 is also required for EcR, and steroid-receptor co-activator (SRC) mediated induction of E74, E75, and HR3. These findings highlight the key role of ecdysone-induced NAA40-mediated histone acetylation in the regulation of metamorphosis. The epigenetic regulator, N(alpha)-acetyltransferase 40 (NAA40), induced by ecdysone, acetylates histone H4 and modulates ecdysone action in the regulation of insect metamorphosis. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

Background: Gut bacteria are beneficial to the host, many of which must be passed on to host offspring. During metamorphosis, the midgut of holometabolous insects undergoes histolysis and remodeling, and thus risks losing gut bacteria. Strategies employed by holometabolous insects to minimize this risk are obscure. How gut bacteria affect host insects after entering the hemocoel and causing opportunistic infections remains largely elusive. Results: We used holometabolous Helicoverpa armigera as a model and found low Lactobacillus load, high level of a C-type lectin (CTL) gene CD209 antigen-like protein 2 (CD209) and its downstream lysozyme 1 (Lys1) in the midgut of the wandering stage. CD209 or Lys1 depletion increased the load of midgut Lactobacillus, which further translocate to the hemocoel. In particular, CD209 or Lys1 depletion, injection of Lactobacillus plantarum, or translocation of midgut L. plantarum into the hemocoel suppressed 20-hydroxyecdysone (20E) signaling and delayed pupariation. Injection of L. plantarum decreased triacylglycerol and cholesterol storage, which may result in insufficient energy and 20E available for pupariation. Further, Lysine-type peptidoglycan, the major component of gram-positive bacterial cell wall, contributed to delayed pupariation and decreased levels of triacylglycerols, cholesterols, and 20E, in both H. armigera and Drosophila melanogaster. Conclusions: A mechanism by which (Lactobacillus-induced) opportunistic infections delay insect metamorphosis was found, namely by disturbing the homeostasis of lipid metabolism and reducing 20E production. Moreover, the immune function of CTL − Lys was characterized for insect metamorphosis by maintaining gut homeostasis and limiting the opportunistic infections. [ABSTRACT FROM AUTHOR]

Simple Summary: Baculovirus infection can prevent the pupation of insects. However, the molecular mechanism of baculovirus preventing the pupation of larvae by regulating the Juvenile hormone (JH) pathway is still unclear. In this study, we examined the interactive relationship of Mamestra brassicae multiple nucleopolyhedroviruses (MbMNPV) and Helicoverpa armigera (H. armigera). We found that MbMNPV infection caused an increased JH titer and inhibited the expression levels of juvenile hormone esterase (JHE) and juvenile hormone epoxide hydrolase (JHEH). Our studies further proved that the JH is mainly degraded by JHE in H. armigera larvae. Knocking down of HaJHE promoted MbMNPV replication. These findings suggest that the infection of H. armigera larvae by MbMNPV leads to an increased JH titer by inhibiting the expression of JHE, which prevents pupation of H. armigera and promotes MbMNPV replication. Baculovirus infection can prevent the pupation of insects. Juvenile hormone (JH) plays a vital role in regulating insect molting and metamorphosis. However, the molecular mechanism of baculovirus preventing the pupation of larvae by regulating the Juvenile hormone (JH) pathway is still unclear. In this study, we found that the Mamestra brassicae multiple nucleopolyhedroviruses (MbMNPV) infection prolonged the larval stage of fourth instar Helicoverpa armigera (H. armigera) by 0.52 d and caused an increase in JH titer. To identify the genes that contribute to the JH increase in H. armigera-MbMNPV interaction, we analyzed mRNA expression profiles of the fat bodies of H. armigera infected by MbMNPV. A total of 3637 differentially expressed mRNAs (DE-mRNAs) were filtered out through RNA-seq analysis. These DE-mRNAs were mainly enriched in Spliceosome, Ribosome biogenesis in eukaryotes, Aminoacyl-tRNA biosynthesis, Mismatch repair, and RNA degradation signaling pathway, which are related to the virus infection. Real-time PCR was used to verify the RNA sequencing results. To find out which genes caused the increase in JH titer, we analyzed all the DE-mRNAs in the transcriptome and found that the JHE and JHEH genes, which were related to JH degradation pathway, were down-regulated. JHE and JHEH genes in the larvae of MbMNPV-infected group were significantly down-regulated compared with the control group by RT-qPCR. We further proved that the JH is degraded by JHE in H. armigera larvae by RNAi, ELISA, RT-qPCR and bioassay, while the hydrolysis of JH by JHEH in H. armigera larvae can almost be ignored. Knocking down of HaJHE promoted the expression of the JH receptor gene Met and the downstream gene Kr-h1, and the replication of MbMNPV. This study clarified that JH is mainly degraded by JHE in H. armigera larvae. The MbMNPV infection of H. armigera larvae leads to the increase of JH titer by inhibiting the expression of JHE. The increase in JH titer promotes the expression of the JH receptor gene Met and the downstream gene Kr-h1, which prevents the pupation of H. armigera, and promotes MbMNPV replication. This study provides new insights into H. armigera and MbMNPV interaction mechanisms. [ABSTRACT FROM AUTHOR]

Nuclear receptors are ligand‐regulated transcription factors that play important role in regulating insect metamorphosis through the ecdysone signalling pathway. In this study, we investigated the nuclear receptor HR38 gene in Bombyx mori (BmHR38), belonging to the NR4A subfamily. BmHR38 mRNA was highly expressed in the head and epidermis at the pupal stage. The expression of the BmHR38 gene was influenced by different doses of 20E at different times. A BmHR38 deletion mutant silkworm was generated using the clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 system. Compared with the wild‐type B. mori, the BmHR38 deletion mutant resulted in abnormal development during the pupal stage, leading to either failed eclosion or the formation of abnormal adult wings. After silencing of BmHR38 in the pupal stage, the phenotype of pupa or moth had no significant change, but it did result in reduced egg production. The mRNA levels of USP, E75 and E74 were significantly increased, while the transcript levels of FTZ‐F1 were suppressed after RNA interference. Furthermore, interference with BmHR38 also inhibited the expressions of chitin metabolism genes, including Chs1, Chs2, Chi, Chi‐h and CDA. Our results suggest that BmHR38 is essential for pupal development and pupa–adult metamorphosis in B. mori by regulating the expression of NRs and chitin metabolism genes. [ABSTRACT FROM AUTHOR]

Simple Summary: The regulation of insect growth and development is intricately governed by the levels of juvenile hormone and 20-hydroxyecdysone. Juvenile hormone esterase is a key catabolic enzyme of juvenile hormone that is involved in the growth, development, and metamorphosis of insects. In this study, we identified the juvenile hormone esterase genes Bmjhe1–9 in silkworm and found that Bmjhe6 was specifically expressed in the silk gland. In order to explore the function of Bmjhe6, the expression of Bmjhe6 was down-regulated in an RNA interference experiment. The results showed that the development of the silk gland was changed as well as the juvenile hormone pathway genes. Interestingly, Bmjhe6 was secreted into the silk gland lumen and cocoon silk, which may have new functions. This study provides some theoretical basis for the regulation of tissue growth and development as well as silk protein synthesis by juvenile hormone esterase, and servers as a reference for the study of juvenile hormone esterase in other insects. Juvenile hormone esterase (JHE) is the specific enzyme that degrades juvenile hormone (JH) and regulates the JH titer in insects. JH also regulates the development of the silk gland and the synthesis and secretion of silk proteins in Bombyx mori. Here, we identified nine possible JHE family members, Bmjhe1–9. Notably, Bmjhe6 is specifically expressed in the silk gland. Using semi-quantitative, quantitative real-time RT-PCR and Western blot, it was confirmed that Bmjhe6 was specifically expressed in the middle silk gland (MSG) with high levels in the anterior region of the MSG (A-MSG). The immunofluorescence localization analysis revealed that Bmjhe6 is produced within cells, secreted into the gland lumen, and co-transported with silk proteins into the anterior silk gland (ASG). In vitro hormone induction experiments demonstrated that Bmjhe6 responds to a JH analog, increasing its expression after 12–24 h, whereas 20-hydroxyecdysone inhibited it. In addition, Bmjhe6 knockdown using dsBmjhe6 injections accelerated larval development, resulting in increased larval body and silk gland weight. This induced disordered sericin genes (Ser2, Ser3) expression, and key genes in the JH synthesis pathway (BmKr-h1 and BmMet1) were significantly upregulated along with the transcription factors (SGF-1 and Sage). These results indicate that Bmjhe6 plays an important role in silk gland growth and silk protein synthesis by modulating JH signal. [ABSTRACT FROM AUTHOR]

Insect metamorphosis fascinated Greek philosophers, bewildered Christian theologians, affirmed the beliefs of Chinese moralists, and continues to mystify science. Yet dramas representing human-animal transformations rarely involve insects. When they do appear, they usually serve as metaphors satirizing human flaws, but are also demeaning to the insect in their simplistic representation. In some 21st-century performances, however, that approach is evolving to better appreciate the multifarious intricacies of insect life. [ABSTRACT FROM AUTHOR]

BACKGROUND: Juvenile hormone (JH) signaling inhibitors may be used as insect growth regulators because of their ability to control metamorphosis and reproduction in insects by regulating the action of JH. RESULTS: We identified ethyl (E)‐3‐(4‐{[7‐ (4‐methoxycarbonylbenzyloxy)‐1,4‐benzodioxan‐6‐yl]methyl}phenyl)prop‐2‐enoate (EMBP) and observed its strong precocious metamorphosis‐inducing activity against silkworm larvae. To further elucidate its mechanism of action, we investigated the effect of EMBP on the JH‐mediated signaling pathway in vitro and in vivo. In a reporter assay using a Bombyx mori cell line, EMBP strongly suppressed the induction of reporter gene expression by Juvenile hormone I (JH I) in a concentration‐dependent manner. A parallel rightward shift was observed in the dose–response curve of JH I after treatment with EMBP, indicating that EMBP competitively inhibited JH. Moreover, we monitored developmental changes in the JH‐responsive gene, Krüppel homolog 1 (Kr‐h1), and ecdysone‐responsive gene, Broad‐Complex (BRC), in EMBP‐treated silkworm larvae. EMBP suppressed only the expression of Kr‐h1 in third‐instar larvae. CONCLUSION: Our results demonstrated that EMBP specifically regulates the JH‐mediated Kr‐h1 signaling pathway. EMBP could be used as a lead compound in the development of new insect growth regulators. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This article features an interview with Gabriela Krejčová and Adam Bajgar, who conducted a study on the role of macrophages in tissue homeostasis during metamorphosis in fruit flies. They found that macrophages convert dying larval adipocytes into nutrients that are utilized by other tissues during post-metamorphic development. The researchers also discuss their scientific backgrounds and the questions their lab is trying to answer. They suggest that the role of macrophages in nutrient recycling may be a universal process in insects and potentially conserved in vertebrates. The article concludes with a discussion of the researchers' hobbies and interests outside of the lab. [Extracted from the article]

Many insects are dependent on microbial mutualists, which are often harbored in specialized symbiotic organs. Upon metamorphosis, insect organs are drastically reorganized. What mechanism regulates the remodeling of the symbiotic organ upon metamorphosis? How does it affect the microbial symbiont therein? Here, we addressed these fundamental issues of symbiosis by experimentally manipulating insect metamorphosis. The stinkbug Plautia stali possesses a midgut symbiotic organ wherein an essential bacterial symbiont resides. By RNAi of master regulator genes for metamorphosis, Kr-h1 over nymphal traits and E93 over adult traits, we generated precocious adults and supernumerary nymphs of P. stali, thereby disentangling the effects of metamorphosis, growth level, developmental stage, and other factors on the symbiotic system. Upon metamorphosis, the symbiotic organ of P. stali was transformed from nymph type to adult type. The supernumerary nymphs and the precocious adults, respectively, developed nymph-type and adult-type symbiotic organs not only morphologically but also transcriptomically, uncovering that metamorphic remodeling of the symbiotic organ is under the control of the MEKRE93 pathway. Transcriptomic, cytological, and biochemical analyses unveiled that the structural and transcriptomic remodeling of the symbiotic organ toward adult emergence underpins its functional extension to food digestion in addition to the original role of symbiont retention for essential nutrient production. Notably, we found that the symbiotic bacteria in the adult-type symbiotic organ up-regulated genes for production of sulfur-containing essential amino acids, methionine and cysteine, that are rich in eggs and sperm, uncovering adult-specific symbiont functioning for host reproduction and highlighting intricate host-symbiont interactions associated with insect metamorphosis. [ABSTRACT FROM AUTHOR]

This article explores the origin of insect metamorphosis, specifically focusing on the role of juvenile hormone in the life cycle of firebrat insects. The study suggests that changing levels of juvenile hormone may have played a significant role in the evolution of metamorphosis. The research indicates that juvenile hormone promotes differentiation and maturation processes in the embryo, marking the end of morphogenesis. The findings also suggest that proteins involved in metamorphosis in hemimetabolous insects may have originated from ancestral ametabolous insects. Further research is needed to understand the molecular mechanisms behind these changes. [Extracted from the article]

The consumption of insects as food and feed has been recently suggested as a possible alternative to the rising global food need, thus it is crucial to monitor any potential food safety hazards in the insect supply chain. The aims of this systematic review were to collect, select, and evaluate studies investigating the persistence of Salmonella in insects. We searched PUBMED, EMBASE, WEB of Science Core Collection, and Food Science and Technology Abstracts. In total, 36 papers investigating the persistence of Salmonella in insects (both holometabolous and heterometabolous) were included after screening. Regarding complete metamorphosis insects, the longest Salmonella persistence was reported in Phormia regina, in which the pathogen persisted for 29 days at 5 °C. Similarly, Salmonella persisted in the feces of Alphitobius diaperinus for 28 days. The incomplete metamorphosis insect showing the longest Salmonella persistence (>10 months) was Blatella germanica. Periplaneta americana excreted Salmonella via feces for 44 days until all the insects were dead. The retrieved data on the persistence of Salmonella can be useful for further analysis by risk assessors and decision-makers involved in the safety of insect-based food, contributing to defining the sanitary requirements and risk mitigation measures along the supply chain. The review protocol is registered in PROSPERO database (CRD42022329213). [ABSTRACT FROM AUTHOR]

Symbiotic interactions between microorganisms and social insects have been described as crucial for the maintenance of these multitrophic systems, as observed for the stingless bee Scaptotrigona depilis and the yeast Zygosaccharomyces sp. SDBC30G1. The larvae of S. depilis ingest fungal filaments of Zygosaccharomyces sp. SDBC30G1 to obtain ergosterol, which is the precursor for the biosynthesis of ecdysteroids that modulate insect metamorphosis. In this work, we find a similar insect-microbe interaction in other species of stingless bees. We analyzed brood cell samples from 19 species of stingless bees collected in Brazil. The osmophilic yeast Zygosaccharomyces spp. was isolated from eight bee species, namely Scaptotrigona bipunctata, S. postica, S. tubiba, Tetragona clavipes, Melipona quadrifasciata, M. fasciculata, M. bicolor, and Partamona helleri. These yeasts form pseudohyphae and also accumulate ergosterol in lipid droplets, similar to the pattern observed for S. depilis. The phylogenetic analyses including various Zygosaccharomyces revealed that strains isolated from the brood cells formed a branch separated from the previously described Zygosaccharomyces species, suggesting that they are new species of this genus and reinforcing the symbiotic interaction with the host insects. [ABSTRACT FROM AUTHOR]

A heterodimeric complex of two nuclear receptors, the ecdysone receptor (ECR) and ultraspiracle (USP), transduces 20-hydroxyecdysone (20E) signaling to modulate insect growth and development. Here, we aimed to determine the relationship between ECR and 20E during larval metamorphosis and also the specific roles of ECR during larval–adult transition in Apis mellifera. We found that ECR gene expression peaked in the 7-day-old larvae, then decreased gradually from the pupae stage. 20E slowly reduced food consumption and then induced starvation, resulting in small-sized adults. In addition, 20E induced ECR expression to regulate larval development time. Double-stranded RNAs (dsRNAs) were prepared using common dsECR as templates. After dsECR injection, larval transition to the pupal stage was delayed, and 80% of the larvae showed prolonged pupation beyond 18 h. Moreover, the mRNA levels of shd, sro, nvd , and spo , and ecdysteroid titers were significantly decreased in ECR RNAi larvae compared with those in GFP RNAi control larvae. ECR RNAi disrupted 20E signaling during larval metamorphosis. We performed rescuing experiments by injecting 20E in ECR RNAi larvae and found that the mRNA levels of ECR, USP, E75, E93 , and Br-c were not restored. 20E induced apoptosis in the fat body during larval pupation, while RNAi knockdown of ECR genes reduced apoptosis. We concluded that 20E induced ECR to modulate 20E signaling to promote honeybee pupation. These results assist our understanding of the complicated molecular mechanisms of insect metamorphosis. [ABSTRACT FROM AUTHOR]

Holometabolous insects undergo metamorphosis to reconstruct their body to the adult form during pupal period. Since pupae cannot take any diets from the outside because of a hard pupal cuticle, those insects stock up on nutrients sufficient for successful metamorphosis during larval feeding period. Among those nutrients, carbohydrates are stored as glycogen or trehalose, which is the major blood sugar in insects. The hemolymph trehalose is constantly high during the feeding period but suddenly decreases at the beginning of the prepupal period. It is believed that trehalase, which is a trehalose-hydrolyzing enzyme, becomes highly active to reduce hemolymph trehalose level during prepupal period. This change in the hemolymph trehalose level has been interpreted as the physiological shift from storage to utilization of trehalose at that stage. Although this shift in trehalose physiology is indispensable for energy production required for successful metamorphosis, little is known on the regulatory mechanisms of trehalose metabolism in accordance with developmental progress. Here, we show that ecdysone, an insect steroid hormone, plays essential roles in the regulation of soluble trehalase activity and its distribution in the midgut of silkworm, Bombyx mori. In the end of larval period, soluble trehalase was highly activated in the midgut lumen. This activation was disappeared in the absence of ecdysone and also restored by ecdysone administration. Our present results suggest that ecdysone is essentially required for the changes in the function of the midgut on trehalose physiology as development progresses. [ABSTRACT FROM AUTHOR]

The control of insect moulting and metamorphosis involves ecdysteroids that orchestrate the execution of developmental genetic programs by binding to dimeric hormone receptors consisting of the ecdysone receptor (EcR) and ultraspiracle (USP). In insects, the main ecdysteroids comprise ecdysone (E), which is synthesized in the prothoracic gland and secreted into the haemolymph, and 20‐hydroxyecdysone (20E), which is considered the active form by binding to the nuclear receptor of the target cell. While biosynthesis of ecdysteroids has been studied in detail in different insects, the transport systems involved in guiding these steroid hormones across cellular membranes have just recently begun to be studied. By analysing RNAi phenotypes in the red flour beetle, Tribolium castaneum, we have identified three transporter genes, TcABCG‐8A, TcABCG‐4D and TcOATP4‐C1, whose silencing results in phenotypes similar to that observed when the ecdysone receptor gene TcEcRA is silenced, that is, abortive moulting and abnormal development of adult compound eyes during the larval stage. The genes of all three transporters are expressed at higher levels in the larval fat body of T. castaneum. We analysed potential functions of these transporters by combining RNAi and mass spectrometry. However, the analysis of gene functions is challenged by mutual RNAi effects indicating interdependent gene regulation. Based on our findings, we propose that TcABCG‐8A, TcABCG‐4D and TcOATP4‐C1 participate in the ecdysteroid transport in fat body cells, which are involved in E → 20E conversion catalysed by the P450 enzyme TcShade. [ABSTRACT FROM AUTHOR]

Simple Summary: Ecdysone is an essential factor affecting host immunity, in addition to regulating insect metamorphosis. There are two isoforms of ecdysone receptors (EcR) in silkworm, BmEcR-B1, and BmEcR-A. In this study, BmEcR-B1 was found to be more critical than BmEcR-A in responding to BmNPV infection. Further studies confirmed that BmEcR-B1 played an anti-BmNPV role in the participation of 20E, which was associated with 20E-induced apoptosis. This study provides theoretical support for elucidating the resistant mechanism of silkworm to BmNPV and the control of BmNPV disease in sericulture. Bombyx mori nucleopolyhedrovirus (BmNPV) is a serious threat to sericulture. Nevertheless, no effective control strategy is currently available. The innate immunity of silkworm is critical in the antiviral process. Exploring its molecular mechanism provides theoretical support for the prevention and treatment of BmNPV. Insect hormone receptors play an essential role in regulating host immunity. We found a correlation between Bombyx mori ecdysone receptor B1 (BmEcR-B1) and BmNPV infection, whereas the underlying mechanism remains unclear. In this study, the expression patterns and sequence characteristics of BmEcR-B1 and its isoform, BmEcR-A, were initially analyzed. BmEcR-B1 was found to be more critical than BmEcR-A in silkworm development and responses to BmNPV. Moreover, RNAi and an overexpression in BmN cells showed BmEcR-B1 had antiviral effects in the presence of 20-hydroxyecdysone (20E); Otherwise, it had no antiviral activity. Furthermore, BmEcR-B1 was required for 20E-induced apoptosis, which significantly suppressed virus infection. Finally, feeding 20E had no significant negative impacts on larval growth and the cocoon shell, suggesting the regulation of this pathway has practical value in controlling BmNPV in sericulture. The findings of this study provide important theoretical support for understanding the mechanism of the silkworm innate immune system in response to BmNPV infection. [ABSTRACT FROM AUTHOR]

20E‐hydroxyecdysone (20E) plays important roles in larval molting and metamorphosis in insects and is also involved in the insect innate immune response. Insect metamorphosis is a highly successful strategy for environmental adaptation and is the most vulnerable stage during which the insect is susceptible to various pathogens. 20E regulates a series of antimicrobial peptides (AMPs) through the immunodeficiency (IMD) pathway activation in Drosophila; nevertheless, whether other immune pathways are involved in 20E‐regulated insect immunity is unknown. Our previous studies showed that BmMD‐2A is a member of the MD‐2‐related lipid recognition (ML) family of proteins that are involved in the Bombyx mori innate immunity Toll signaling pathway. In this study, we further demonstrate that BmMD‐2A is also positively regulated by 20E, and the BmMD‐2A neutralization experiment suggested that 20E activates some downstream immune effect factors, the AMP genes against Escherichia coli and Staphylococcus aureus, through the regulation of BmMD‐2A in larval metamorphosis, implying that B. mori may use the Toll‐ML signaling pathway to maintain innate immune balance in the larval‐pupal metamorphosis stage, which is a different innate immunity pathway regulated by 20E compared to the IMD pathway in Drosophila. [ABSTRACT FROM AUTHOR]

Simple Summary: The English grain aphid, Sitobion avenae, is one of the major pests and disease vectors of wheat crops. In this study, E75, a key gene associated with ecdysone signal pathway, was identified and cloned from S. avenae. Functional characterization of E75 confirmed its role in the regulation of growth, development, and molting process of aphids. This finding offers a potential molecular target for the subsequent development of genetic-based biopesticides for aphid control. Ecdysteroid hormones are key regulators of insect development and metamorphosis. Ecdysone-inducible E75, a major component of insect ecdysone signaling pathway, has been well characterized in holometabolous insects, however, barely in hemimetabolous species. In this study, a total of four full-length E75 cDNAs from the English grain aphid, Sitobion avenae, were identified, cloned, and characterized. The four SaE75 cDNAs contained 3048, 2625, 2505, and 2179 bp open reading frames (ORF), encoding 1015, 874, 856, and 835 amino acids, respectively. Temporal expression profiles showed that SaE75 expression was low in adult stages, while high in pseudo embryo and nymphal stages. SaE75 was differentially expressed between winged and wingless morphs. RNAi-mediated suppression of SaE75 led to substantial biological impacts, including mortality and molting defects. As for the pleiotropic effects on downstream ecdysone pathway genes, SaHr3 (hormone receptor like in 46) was significantly up-regulated, while Sabr-c (broad-complex core protein gene) and Saftz-f1 (transcription factor 1) were significantly down-regulated. These combined results not only shed light on the regulatory role of E75 in the ecdysone signaling pathway, but also provide a potential novel target for the long-term sustainable management of S. avenae, a devastating global grain pest. [ABSTRACT FROM AUTHOR]

Essential oils (EOs) are a promising source for novel environmentally safe insecticides. However, the structural diversity of their compounds poses challenges to accurately elucidate their biological mechanisms of action. We present a new chemoinformatics methodology aimed at predicting the impact of essential oil (EO) compounds on the molecular targets of commercial insecticides. Our approach merges virtual screening, chemoinformatics, and machine learning to identify custom signatures and reference molecule clusters. By assigning a molecule to a cluster, we can determine its most likely interaction targets. Our findings reveal that the main targets of EOs are juvenile hormone-specific proteins (JHBP and MET) and octopamine receptor agonists (OctpRago). Three of the twenty clusters show strong similarities to the juvenile hormone, steroids, and biogenic amines. For instance, the methodology successfully identified E-Nerolidol, for which literature points indications of disrupting insect metamorphosis and neurochemistry, as a potential insecticide in these pathways. We validated the predictions through experimental bioassays, observing symptoms in blowflies that were consistent with the computational results. This new approach sheds a higher light on the ways of action of EO compounds in nature and biotechnology. It also opens new possibilities for understanding how molecules can interfere with biological systems and has broad implications for areas such as drug design. [ABSTRACT FROM AUTHOR]

20-Hydroxyecdysone (20E) plays an essential role in coordinating developmental transitions in insects through responsive protein-coding genes and microRNAs (miRNAs). However, the interplay between 20E and miRNAs during insect metamorphosis is unknown. In this study, using small RNA sequencing, a comparative miRNA transcriptomic analysis in different development stages, and 20E treatment, we identified ame-bantam-3p as a key candidate miRNA involved in honeybee metamorphosis. Target prediction and in vitro dual-luciferase assays confirmed that ame-bantam-3p interacts with the coding region of the megf8 gene and promotes its expression. Meanwhile, temporal expression analysis revealed that the expression of ame-bantam-3p is higher in the larval stage than in prepupal and pupal stages, and that this expression pattern is similar to that of megf8. In vivo, we found that the mRNA level of megf8 was significantly increased after the injection of ame-bantam-3p agomir. A 20E feeding assay showed that 20E downregulated the expression of both ame-bantam-3p and its target gene megf8 on larval days five, six, and seven. Meanwhile, the injection of ame-bantam-3p agomir also reduced the 20E titer, as well as the transcript levels of essential ecdysteroid synthesis genes, including Dib, Phm, Sad, and Nvd. The transcript levels of 20E cascade genes, including EcRA, ECRB1, USP, E75, E93, and Br-c, were also significantly decreased after ame-bantam-3p agomir injection. However, ame-bantam-3p antagomir injection and dsmegf8 injection showed the opposite effect to ame-bantam-3p agomir injection. Ame-bantam-3p agomir treatment ultimately led to mortality and the failure of larval pupation by inhibiting ecdysteroid synthesis and the 20E signaling pathway. However, the expression of 20E signaling-related genes was significantly increased after megf8 knockdown, and larvae injected with dsmegf8 showed early pupation. Combined, our results indicate that ame-bantam-3p is involved in the 20E signaling pathway through positively regulating its target gene megf8 and is indispensable for larval–pupal development in the honeybee. These findings may enhance our understanding of the relationship between 20E signaling and small RNAs during honeybee development. [ABSTRACT FROM AUTHOR]

ABSTRACT Microbes found in the digestive tracts of insects are known to play an important role in their host’s behavior. Although Lepidoptera is one of the most varied insect orders, the link between microbial symbiosis and host development is still poorly understood. In particular, little is known about the role of gut bacteria in metamorphosis. Here, we explored gut microbial biodiversity throughout the life cycle of Galleria mellonella, using amplicon pyrosequencing with the V1 to V3 regions, and found that Enterococcus spp. were abundant in larvae, while Enterobacter spp. were predominant in pupae. Interestingly, eradication of Enterococcus spp. from the digestive system accelerated the larval-to-pupal transition. Furthermore, host transcriptome analysis demonstrated that immune response genes were upregulated in pupae, whereas hormone genes were upregulated in larvae. In particular, regulation of antimicrobial peptide production in the host gut correlated with developmental stage. Certain antimicrobial peptides inhibited the growth of Enterococcus innesii, a dominant bacterial species in the gut of G. mellonella larvae. Our study highlights the importance of gut microbiota dynamics on metamorphosis as a consequence of the active secretion of antimicrobial peptides in the G. mellonella gut. IMPORTANCE First, we demonstrated that the presence of Enterococcus spp. is a driving force for insect metamorphosis. RNA sequencing and peptide production subsequently revealed that antimicrobial peptides targeted against microorganisms in the gut of Galleria mellonella (wax moth) did not kill Enterobacteria species, but did kill Enterococcus species, when the moth was at a certain stage of growth, and this promoted moth pupation.

Recent studies have documented global declines in insects and their relatives, but the exact mechanisms explaining these patterns are not fully understood. A potential driver underlying arthropod population declines is increases in anthropogenic inputs of nitrogen (N) and phosphorus (P). Here, we synthesize the effects of N, P, and combined N + P enrichment on the abundance of hexapods (insects and collembola) and arachnids from 901 experiments reported in 84 studies. We found that N and combined N + P enrichment caused significant decreases in the abundance of these groups overall. While arthropod responses to nutrient enrichment across aquatic and terrestrial habitats and in temperate as well as tropical climatic zones differed in magnitude, our results suggest that arthropods are decreasing similarly in response to nitrogen and phosphorus enrichment. Further, despite previously shown differences in the nutrient demands of different insect metamorphosis groups, we found consistent negative effects of N + P enrichment on all groups. Our results also showed that the negative effects of nutrient additions are stronger for aquatic insects that are considered more sensitive to changes in physical–chemical parameters in their environments, Ephemeroptera, Plecoptera, and Trichoptera (EPT), compared with other aquatic insects. In addition, N + P enrichment reduced the abundance of above‐ground and below‐ground arthropods, suggesting that a similar mechanism driving arthropod community change is acting on both groups. These findings suggest that changes in elemental cycles are a potential cause of the ongoing global decline of arthropods and underscore the serious effects of nutrient enrichment on ecological systems. [ABSTRACT FROM AUTHOR]

Mammalian puberty and Drosophila metamorphosis, despite their evolutionary distance, exhibit similar design principles and conservation of molecular components. In this Viewpoint, we review recent advances in this area and the similarities between both processes in terms of the signaling pathways and neuroendocrine circuits involved. We argue that the detection and uptake of peripheral fat by Drosophila prothoracic endocrine cells induces endomembrane remodeling and ribosomal maturation, leading to the acquisition of high biosynthetic and secretory capacity. The absence of this fat–neuroendocrine interorgan communication leads to giant, obese, non‐pupating larvae. Importantly, human leptin is capable of signaling the pupariation process in Drosophila, and its expression prevents obesity and triggers maturation in mutants that do not pupate. This implies that insect metamorphosis can be used to address issues related to the biology of leptin and puberty. [ABSTRACT FROM AUTHOR]

The neuropeptide prothoracicotropic hormone (PTTH) plays a key role in regulating ecdysone synthesis and promoting insect metamorphosis. Pyriproxyfen is a juvenile hormone analogue. We previously reported that pyriproxyfen disrupts ecdysone secretion and inhibits larval-pupal metamorphosis in silkworms. However, the specific molecular mechanisms by which pyriproxyfen interferes with ecdysone signaling remain to be elucidated. Herein, the RNA-seq analysis on the ecdysone-secretion organ prothoracic gland (PG) was conducted following pyriproxyfen exposure. A total of 3774 differentially expressed genes (DEGs) were identified, with 1667 up-regulated and 2107 down-regulated. KEGG analysis showed that DEGs were enriched in the MAPK signaling pathway, a conserved pathway activated by PTTH binding to Torso, which regulates the ecdysone synthesis. qRT-PCR results indicated a significant up-regulation in PTTH transcription level, while the transcription levels of torso and downstream MAPK pathway genes, Ras2 , Raf and ERK , were down-regulated 24 h post-pyriproxyfen treatment. Consistent with these transcriptional changes, PTTH titers in the brain also increased following pyriproxyfen treatment. These results suggest that pyriproxyfen induces abnormal metamorphosis in silkworms by impairing PTTH-Torso signaling. This study enhances our understanding of the molecular mechanisms of pyriproxyfen-induced larval-pupal abnormal metamorphosis in silkworms, and also provides insights for developing detoxification strategies for juvenile hormone analog pesticides to non-target organisms. [Display omitted] • Pyriproxyfen disrupted the interaction of prothoracicotropic hormone with its receptor Torso. • The prothoracicotropic hormone's receptor Torso may be a potential target of pyriproxyfen. • Pyriproxyfen stimulated the phosphorylation of ERK protein. [ABSTRACT FROM AUTHOR]

Carboxypeptidase A has been found across various animal species, yet its activation mechanism during the insect molting process remains elusive. Our study specifically delved into the activation mechanism of carboxypeptidase A (Bm-CPA), identified in Bombyx mori 's molting fluid during metamorphosis. Initially, western blotting identified two forms of Bm-CPA, 65 kDa and 54 kDa, in the epidermis of silkworms during the molting stage. Expressing the complete Bm-CPA sequence in Pichia pastoris allowed the identification, via mass spectrometry analysis, of a 75-amino-acid propeptide for the initial hydrolysis process. Subsequently, a 35 kDa form of Bm-CPA emerged in the molting fluid, confirmed as the active form through in vitro assays, demonstrating potent carboxypeptidase A activity and faint carboxypeptidase B activity. Four potential activation sites (including Lys158/Arg159 and Arg177/Arg178) were identified through mass spectrometry and amino acid mutation analysis. RNAi of Bm-CPA indicates its critical role in molting. Finally, the carboxypeptidase inhibitor (Bm-CPI) from silkworm molting fluid was expressed to explore its role in regulating Bm-CPA activity, demonstrating a direct interaction with the 35 kDa Bm-CPA. Our research implies Bm-CPA's potential involvement in the silkworm molting process, suggesting diverse regulatory roles. These findings highlight intricate protein regulation patterns during insect metamorphosis and development. [Display omitted] • Three distinct molecular weights of Bm-CPA are present in the epidermis and molting fluid of silkworms. • Bm-CPA undergoes two proteolytic cleavages for activation. • Bm-CPA has four potential activation sites, including Lys158/Arg159 and Arg177/Arg178. • RNAi of Bm-CPA results in silkworms failing to molt. • Bm-CPI inhibits the activity of Bm-CPA but does not affect its activation process. [ABSTRACT FROM AUTHOR]

Juvenile hormones (JHs) control insect metamorphosis and reproduction. JHs act through a receptor complex consisting of methoprene-tolerant (Met) and taiman (Tai) proteins to induce transcription of specific genes. Among chemically diverse synthetic JH mimics (juvenoids), some of which serve as insecticides, unique peptidic juvenoids stand out as being highly potent yet exquisitely selective to a specific family of true bugs. Their mode of action is unknown. Here we demonstrate that, like established JH receptor agonists, peptidic juvenoids act upon the JHR Met to halt metamorphosis in larvae of the linden bug, Pyrrhocoris apterus. Peptidic juvenoids induced ligand-dependent dimerization between Met and Tai proteins from P. apterus but, consistent with their selectivity, not from other insects. A cell-based split-luciferase system revealed that the Met-Tai complex assembled within minutes of agonist presence. To explore the potential of juvenoid peptides, we synthesized 120 new derivatives and tested them in Met-Tai interaction assays. While many substituents led to loss of activity, improved derivatives active at sub-nanomolar range outperformed hitherto existing peptidic and classical juvenoids including fenoxycarb. Their potency in inducing Met-Tai interaction corresponded with the capacity to block metamorphosis in P. apterus larvae and to stimulate oogenesis in reproductively arrested adult females. Molecular modeling demonstrated that the high potency correlates with high affinity. This is a result of malleability of the ligand-binding pocket of P. apterus Met that allows larger peptidic ligands to maximize their contact surface. Our data establish peptidic juvenoids as highly potent and species-selective novel JHR agonists. [ABSTRACT FROM AUTHOR]

The disproportionate growth of insect appendages such as facultative growth of wings and exaggeration of beetle horns are examples of phenotypic plasticity. Insect metamorphosis is the critical stage for development of pupal and adult structures and degeneration of the larval cells. How the disproportionate growth of external appendages is regulated during tissue remodeling remains unanswered. Tribolium castaneum is used as a model to study the function of mitochondria in metamorphosis. Mitochondrial dysfunction is achieved by the knockdown of key mitochondrial regulators. Here we show that mitochondrial function is not required for metamorphosis except that severe mitochondrial dysfunction blocks ecdysis. Surprisingly, various abnormal wing growth, including short and wingless phenotypes, are induced after knocking down mitochondrial regulators. Mitochondrial activity is regulated by IIS (insulin/insulin-like growth factor signaling)/FOXO (forkhead box, sub-group O) pathway through TFAM (transcription factor A, mitochondrial). RNA sequencing and differential gene expression analysis show that wing-patterning and insect hormone response genes are downregulated, while programmed cell death and immune response genes are upregulated in insect wing discs with mitochondrial dysfunction. These studies reveal that mitochondria play critical roles in regulating insect wing growth by targeting wing development during metamorphosis, thus showing a novel molecular mechanism underlying developmental plasticity. Mitochondrial disruption in the red flour beetle leads to insects with three layers of cuticles (larval, pupal, and adult) and blocks the wing development. [ABSTRACT FROM AUTHOR]

The feeding activity of Plutella xylostella in brassica crops can lead to large losses; thus, pesticides that prevent feeding during the larval stage or prevent the metamorphosis of this insect can be used for its control. In this study, the effects of two types of aqueous extracts of Tradescantia pallida on the different life stage of P. xylostella cycle were tested; neither of the two aqueous extracts, which were obtained by infusion and maceration, had been tested against P. xylostella. The biological variables evaluated were larval and pupal duration and viability, pupal weight, sex ratio, longevity of females, fecundity, fertility and oviposition period. There was no significant difference in the duration of the larval phase of P. xylostella between the bioassay treatments; however, larval viability was lower when the individuals were exposed to both types of T. pallida extracts. Reduced pupal viability was observed among the individuals treated with the application of the extracts. Treatment with the aqueous extract obtained by infusion caused the lowest pupal weight, fecundity, and fertility and longevity among females. The results obtained in this study allow us to propose the bioextract as an alternative for pest management, emphasizing the technique for small producers and/or organic. [ABSTRACT FROM AUTHOR]

The corpora allata and the prothoracic glands control moulting and metamorphosis in insects. These endocrine glands are specified in the maxillary and labial segments at positions homologous to those forming the trachea in more posterior segments. Glands and trachea can be homeotically transformed into each other suggesting that all three evolved from a metamerically repeated organ that diverged to form glands in the head and respiratory organs in the trunk. While much is known about tracheal specification, there is limited information about corpora allata and prothorathic gland specification. Here we show that the expression of a key regulator of early gland development, the snail gene, is controlled by the Dfd and Scr Hox genes and by the Hedgehog and Wnt signalling pathways that induce localised transcription of upd, the ligand of the JAK/STAT signalling pathway, which lies at the heart of gland specification. Our results show that the same upstream regulators are required for the early gland and tracheal primordia specification, reinforcing the hypothesis that they originated from a segmentally repeated organ present in an ancient arthropod. Author summary: The main endocrine organs controlling insect moulting and metamorphosis are the corpora allata and the prothoracic glands. Genetic experiments in Drosophila melanogaster suggested that, despite their extremely different morphology and function, the corpora allata and the prothoracic glands are homologous to the respiratory trachea. All three organs derive from a primordium arising at similar locations along the cephalic and trunk segments, they activate common developmental genes using the same cis-regulatory elements, and can be transformed into each other by modifying Hox expression. One key difference between glands and trachea is that the endocrine primordia activate the Epithelial to Mesenchymal inducer gene snail. Using the snail gland specific enhancer as a proxy for gland formation, we show that the glands are specified by the same inputs specifying the trachea. These include the JAK/STAT, the Hedgehog and Wingless signalling pathways as well as inputs from the Hox genes. These observations support the hypothesis that during arthropod evolution, a metamerically repeated organ diverged to give rise to endocrine glands in the head and respiratory organs in the trunk segments. [ABSTRACT FROM AUTHOR]

Abstract Background The zinc-finger transcription factor Krüppel-homolog 1 (Kr-h1) exerts a dual regulatory role during insect development by preventing precocious larval/nymphal metamorphosis and in stimulating aspects of adult reproduction such as vitellogenesis. However, how Kr-h1 functions both as a transcriptional repressor in juvenile metamorphosis and an activator in adult reproduction remains elusive. Here, we use the insect Locusta migratoria to dissect the molecular mechanism by which Kr-h1 functions as activator and repressor at these distinct developmental stages. Results We report that the kinase PKCα triggers Kr-h1 phosphorylation at the amino acid residue Ser154, a step essential for its dual functions. During juvenile stage, phosphorylated Kr-h1 recruits a corepressor, C-terminal binding protein (CtBP). The complex of phosphorylated Kr-h1 and CtBP represses the transcription of Ecdysone induced protein 93F (E93) and consequently prevents the juvenile-to-adult transition. In adult insects, phosphorylated Kr-h1 recruits a coactivator, CREB-binding protein (CBP), and promotes vitellogenesis by inducing the expression of Ribosomal protein L36. Furthermore, Kr-h1 phosphorylation with the concomitant inhibition of E93 transcription is evolutionarily conserved across insect orders. Conclusion Our results suggest that Kr-h1 phosphorylation is indispensable for the recruitment of transcriptional cofactors, and for its anti-metamorphic and vitellogenic actions in insects. Our data shed new light on the understanding of Kr-h1 regulation and function in JH-regulated insect metamorphosis and reproduction.

Juvenile hormone (JH) signalling, via its receptor Methoprene-tolerant (Met), controls metamorphosis and reproduction in insects. Met belongs to a superfamily of transcription factors containing the basic Helix Loop Helix (bHLH) and Per Arnt Sim (PAS) domains. Since its discovery in 1986, Met has been characterized in several insect species. However, in spite of the importance as vectors of Chagas disease, our knowledge on the role of Met in JH signalling in Triatominae is limited. In this study, we cloned and sequenced the Dipetalogaster maxima Met transcript (DmaxMet). Molecular modelling was used to build the structure of Met and identify the JH binding site. To further understand the role of the JH receptor during oogenesis, transcript levels were evaluated in two main target organs of JH, fat body and ovary. Functional studies using Met RNAi revealed significant decreases of transcripts for vitellogenin (Vg) and lipophorin (Lp), as well as their receptors. Lp and Vg protein amounts in fat body, as well as Vg in hemolymph were also decreased, and ovarian development was impaired. Overall, these studies provide additional molecular insights on the roles of JH signalling in oogenesis in Triatominae; and therefore are relevant for the epidemiology of Chagas´ disease. [ABSTRACT FROM AUTHOR]

Background: Insect 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. Results: During 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). Conclusions: This 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. [ABSTRACT FROM AUTHOR]

Spodoptera litura (Fabricius) is a polyphagous pest causing economic losses to a number of agriculturally important crops. The present study aimed to investigate the changes in bacterial diversity during metamorphosis of insect using culturable techniques. Based on 16S rRNA sequencing, seventeen culturable bacteria were identified from different development stages of S. litura. Firmicutes were found to be the most abundant followed by Proteobacteria and Actinobacteria. The bacterial diversity varied across different developmental stages as indicated by Simpson and Shannon indices. The eggs supported less diverse bacterial flora consisting of Staphylococcus species. Further, different larval instars had a common baseline distribution of bacterial flora, with some bacterial species observed in specific instars only. The bacterial diversity decreased in the late pupal stage. The gut bacterial communities differed in male and female with Proteobacteria being more prominent in the later. Gut bacteria are known to play important role in host nutrition, digestion, detoxification, reproduction, communication etc. Therefore, in order to determine their functional role, S. litura larvae were fed on diet enriched with bacteria. None of the bacterial isolate influenced the fitness in terms of growth and development of S. litura. However, Serratia marcescens, Klebsiella pneumoniae and Pseudomonas paralactis lead to decrease the survival of S. litura. These results indicate that metamorphosis influences the gut bacterial diversity and the association between S. litura and its gut bacteria may be commensal or pathogenic. The study on culturable bacterial flora may pave the way to develop sustainable and environment friendly pest management approaches. [ABSTRACT FROM AUTHOR]

Hormone receptor 3 (HR3), an early-late gene of the 20-hydroxyecdysone (20E) signaling pathway, plays a critical role in insect metamorphosis and development. In this study, we identified and characterized an HR3 gene (LsHR3) from the cigarette beetle, Lasioderma serricorne. The open reading frame of LsHR3 is 1581 bp encoding a 527 amino acid protein that contains a conserved DNA binding domain and a ligand binding domain. LsHR3 was mainly expressed in the fourth-instar larvae, prepupae, and pupae and showed high expression in the fat body. The expression of LsHR3 was induced by 20E, while it was significantly suppressed by silencing of six 20E synthesis and signaling pathway genes. RNA interference (RNAi)-aided knockdown of LsHR3 in the fourth-instar larvae disrupted the larval–pupal molting and caused 100% mortality. The 20E titer of LsHR3-depletion larvae was decreased, and expressions of five 20E synthesis genes were dramatically decreased. Silencing LsHR3 reduced chitin content and downregulated the expression of genes involved in chitin synthesis and degradation. Hematoxylin and eosin staining of abdominal cuticle showed that no apolysis occurred after silencing LsHR3. These results suggest that LsHR3-mediated 20E signaling is involved in the regulation of chitin metabolism during the molting process of L. serricorne, and targeting this gene by RNAi has potential in controlling this pest. [ABSTRACT FROM AUTHOR]