The Evolution of Insect Metamorphosis

Knockdown of farnesyl pyrophosphate synthetase gene TuFPPS by RNAi extends quiescent period and halts molting of the spider mite, Tetranychus urticae

In insects, farnesyl pyrophosphate synthase (FPPS), a pivotal enzyme in the mevalonate pathway, is crucial in the juvenile hormone (JH)/methyl farnesoate (MF) biosynthesis pathway, particularly regulating the molting process. However, its role in the post-embryonic development and molting in Acari remains unclear. This study therefore investigated the function of TuFPPS in the deutonymphal stage of the two-spotted spider mite, Tetranychus urticae, an important pest in agriculture. Real time quantitative PCR (qPCR) revealed a significant increase in TuFPPS expression in the middle of the quiescent period (28 h). RNA interference (RNAi)-mediated knockdown of TuFPPS caused developmental delays, notably extending the quiescent period and delaying the molting process. Ultimately, the treated mites failed to molt and died with 80% mortality at 108 h before molting, while > 90% of the mites in the control successfully molted. To investigate the potential functions of TuFPPS during the quiescent period and molting process in T. urticae, we performed a genome-wide RNA sequencing following RNAi knockdown of TuFPPS. Four genes were identified based on the thresholds of|FC| ≥ 3 and FDR < 0.05, and these are involved in carbohydrate metabolism, fatty acid and lipid metabolism, amino acid metabolism, and ABC transporters. Altogether, our data suggest that TuFPPS plays a critical role in regulating energy transport, intracellular digestion, and energy supply, as seen in ametabolous insects. These findings lay the foundation for further studies of the molecular mechanism of JH/MF in post-embryonic development and molting in mites, and also identify a potential target for pest control, as demonstrated in T. urticae.

Role of histone methylation in insect development: KMT5A regulates ecdysteroid biosynthesis during metamorphosis of Tribolium castaneum

Methylation levels of core histones play important roles in the regulation of gene expression and impact animal development. However, the methyltransferases and demethylases that determine histone methylation levels remain largely unexplored in insects. Most of our current understanding of histone methylation comes from mammalian studies. In this study, we first identified potential histone methyltransferases and demethylases encoded in the genome of the red flour beetle Tribolium castaneum. The function of these histone methylation enzymes in the metamorphosis was investigated by knocking down genes coding for these enzymes using RNA interference (RNAi). Our results showed that a lysine methyltransferase, KMT5A, plays a critical role in T. castaneum metamorphosis by regulating the biosynthesis of ecdysteroids. Treating KMT5A-knockdown larvae with 20 hydroxyecdysone can partially rescue T. castaneum pupation. Western blot analysis showed that KMT5A catalyzes H4K20 mono-methylation. However, further studies suggest that KMT5A may regulate T. castaneum pupation through mechanisms independent of H4K20 methylation. These data uncovered the roles of histone methylation enzymes in T. castaneum metamorphosis and KMT5A as a critical regulator of ecdysteroid biosynthesis.

Symbiotic bracovirus of a parasite modulate host ecdysis process

Parasitoids modulate host development for the survival of their offspring, but the mechanisms underlying this phenomenon remain largely unknown. Here, we found that the endoparasitoid Cotesia vestalis disrupted the larval-larval ecdysis in its host Plutella xylostella by the 20-hydroxyecdysone (20E) synthesis pathway. After parasitization by C. vestalis, the 20E peak of host larvae disappeared before the onset of ecdysis and the expression of ecdysone synthesis genes was significantly downregulated. We further found that a Cotesia vestalis bracovirus (CvBV) gene CvBV_28 - 5 was transiently high-level expressed prior to the host's 20E peak, enabling the precise suppression of this critical developmental signal. Consistently, the knockdown of CvBV_28 - 5 affected the expression of 20E response transcription factors in the cuticle and several ecdysis-related genes. Furthermore, we found that CvBV_28 - 5 bound directly to the Raf, a MAP3K member of the MAPK pathwaythat functions as a critical regulator of ecdysone synthesis genes in hosts. Collectively, our results provide the first evidence that parasitoids modulate host ecdysis by affecting MAPK-20E signaling during a defined developmental window and provide novel insights into the mechanism of parasitoid regulation of host development.

Environmental yeasts differentially impact the development and oviposition behavior of the Asian tiger mosquito Aedes albopictus

BACKGROUND

While the Asian tiger mosquito (Aedes albopictus), a known vector of many arboviruses, establishes symbiotic associations with environmentally acquired yeasts, their impact on mosquito biology remains poorly investigated. To better understand these associations, we hypothesized that waterborne yeasts colonizing the larval gut differentially support mosquito development based on their capacity to produce riboflavin or recycle nitrogen waste into proteins by secreting uricase, as B vitamins and amino acids are crucial for mosquito development. To address this hypothesis, we used axenic and gnotobiotic insects to gauge the specific impact of different environmental yeasts on Ae. albopictus development and survival. We then evaluated whether the observed variations across yeast species could be linked to differential uricolytic activities and varying quantities of riboflavin and proteins in insecta. Finally, given that mosquito oviposition site selection favors conditions that enhance offspring performance, we tested whether yeasts that promote faster development mediate oviposition site selection by gravid females.

RESULTS

Differences in mosquito development times were observed based on the environmental yeast used. Yeasts like Rhodotorula mucilaginosa and Aureobasidium pullulans promoted rapid development and were associated with improved survival. Conversely, yeasts such as Torulaspora delbrueckii and Martiniozyma asiatica, which led to slower development, produced smaller adults. Notably, R. mucilaginosa, which promoted the fastest development, provided high riboflavin intakes and enhance nitrogenous waste recycling and protein synthesis through strong uricolytic-ureolytic activity. Behavioral experiments indicated that yeasts promoting rapid development "attract gravid females.

CONCLUSIONS

Our findings highlight that a set of environmental yeasts present in natural larval breeding sites can be associated with improved mosquito development and survival by enhancing nutritional intake, thereby attracting gravid females. Variations in mosquito development time are likely linked to the differential levels of riboflavin production and nitrogenous waste recycling capacities among yeast species. This study opens new perspectives on the trophic interactions between mosquitoes and their mycobiota, emphasizing the importance of nitrogen-containing molecules such as essential amino acids, proteins, or vitamins provided by the mycobiota. Video Abstract.

Transcriptional induction by ecdysone in Drosophila salivary glands involves an increase in chromatin accessibility and acetylation

Transcriptional activation by 20-hydroxyecdysone (20E) in Drosophila provides an excellent model for studying tissue-specific responses to steroids. An increase in the 20E concentration regulates the degradation of larval and the proliferation of adult tissues during metamorphosis. To study 20E-dependent transcription, we used the natural system for controlling the 20E concentration-the E23 membrane transporter-which exports 20E from the cell. We artificially expressed E23 in tissues to suppress the first wave of 20E-inducible transcription at metamorphosis. E23 expression revealed a plethora of 20E-dependent genes in salivary glands, while mildly affecting transcription in brain. We described the mechanisms controlling transcriptional activation by 20E in salivary glands. 20E depletion decreased the binding of Pol II and the TFIID subunit, TBP, to the promoters of primary targets, demonstrating the role of 20E in transcription initiation. At target loci, 20E depletion resulted in the malfunctioning of sites co-bound with EcR and CBP/Nejire and enriched for the H3K27Ac mark inherent to active enhancers. At these sites, the 20E concentration was found to control chromatin accessibility and acetylation. We suggest that the activity of these 'active' ecdysone-sensitive elements was responsible for the active status of 20E targets in the salivary glands of wandering larvae.

Assessment of MALDI-TOF MS for Arthropod Identification Based on Exuviae Spectra Analysis

MALDI-TOF MS is an innovative tool for identifying hematophagous and non-hematophagous arthropods at various life stages. However, identification by MALDI-TOF MS currently requires euthanizing of the specimen, hindering further phenotypic tests. All arthropods have a common factor, molting of their exoskeletons leaving a remaining structure known as the exuviae. This phenomenon is indispensable for their growth and can evidence past arthropod presence. This study assessed the performance of MALDI-TOF MS biotyping for arthropod identification using exuviae from nine distinct laboratory-reared species (Aedes aegypti, Anopheles coluzzii, Cimex lectularius, C. hemipterus, Pediculus humanus humanus, Triatoma infestans, Rhodnius prolixus, Supella longipalpa and Blattella germanica) compared its efficiency with a molecular identification approach using DNA sequencing. Molecular analysis showed low DNA quantity in exuviae (n = 108) across species, resulting in low success of COI, 16s, and 18s amplification (50.0%), depending on the species and sequencing (10.2%). The establishment of an exuviae protocol for MS submission yielded spectra of high reproducibility and specificity per species. After upgrading a homemade reference MS database with exuviae spectra, a query with remaining spectra revealed that 100% of samples were correctly identified, with 85.8% (278/324) exceeding the threshold score value for reliable identification. MALDI-TOF MS showed high efficiency in identifying various arthropod species based on their exuviae. This approach is a groundbreaking development in the field of entomology underlining that MALDI-TOF outperformed traditional methods of exuviae identification, including morphological and molecular tools. It also prevents specimen sacrifice which could be used for complementary analyses.

Developmental Genetic and Molecular Analysis of Drosophila Central Complex Lineages

Complex behaviors are mediated by a diverse class of neurons and glia produced during development. Both neural stem cell-intrinsic and -extrinsic temporal cues regulate the appropriate number, molecular identity, and circuit assembly of neurons. The Drosophila central complex (CX) is a higher-order brain structure regulating various behaviors, including sensory-motor integration, celestial navigation, and sleep. Most neurons and glia in the adult CX are formed during larval development by 16 Type II neural stem cells (NSCs). Unlike Type I NSCs, which directly give rise to the ganglion mother cells (GMCs), Type II NSCs give rise to multiple intermediate neural progenitors (INPs), and each INP in turn generates multiple GMCs, hence fostering the generation of longer and more diverse lineages. This makes Type II NSCs a suitable model to unravel the molecular mechanisms regulating neural diversity in more complex lineages. In this review, we elaborate on the classification and identification of NSCs based on the types of division adopted and the molecular markers expressed in each type. In the end, we discuss genetic methods for lineage analysis and birthdating. We also explain the temporal expression of stem cell factors and genetic techniques to study how stem cell factors may regulate neural fate specification.

Knockout BR-C induces premature expression of E93 thus triggering adult differentiation under larval morphology

BACKGROUND

Holometabolan pupal-specifier broad-complex (BR-C) and adult specifier ecdysone-induced protein 93F (E93) are essential for metamorphosis; however, their interaction and effects on programmed cell death and cell differentiation during pupation remain unclear.

RESULTS

Here, multiple single-guide RNA (sgRNA)-mediated mosaic knockout of BR-C induced a deformed larva/pupa intermediate phenotype in Spodoptera frugiperda. Quantitative real-time polymerase chain reaction (qPCR) analysis showed that the adult specifier E93 was prematurely expressed in the BR-C mutants during the penultimate and last instar larval stages. Additionally, histological observation and TUNEL assay showed that apoptosis in the fat body and midgut was activated in the larval tissues; astonishingly, the adult midgut appeared in the pupae of BR-C mutants.

CONCLUSION

Overall, the results demonstrated that the premature expression of E93 induced by lack of BR-C triggers adult differentiation during the larval stages, which revealed the inhibitory effect of BR-C on E93 during metamorphosis in S. frugiperda. © 2024 Society of Chemical Industry.

Pseudogerm of the parasitoid Macrocentrus cingulum suppresses host pupation by degenerating prothoracic gland and inhibiting the expression of Br-C in the host Ostrinia furnacalis

BACKGROUND

Parasitic wasps manipulate host development for successful parasitization. When the host Ostrinia furnacalis is parasitized by the parasitoid Macrocentrus cingulum, its larvae fail to pupate and are consumed as nutrition by the wasp larvae. However, the mechanism by which M. cingulum modulates host pupation remains unclear. This study reports on pseudogerm, a newly discovered parasitic factor derived from M. cingulum, which plays a regulatory role in the pupation process of the host.

RESULTS

Ostrinia furnacalis larvae transplanted with pseudogerms failed to pupate, and their prothoracic gland (PG) cells did not enlarge significantly at the prepupal stage compared to the control. Additionally, the nuclei of PG cells fragmented, the number of secretory vesicles in the cytoplasm decreased markedly, and the intracellular channel system on the cell membrane atrophied. Furthermore, the elevation of the 20-hydroxyecdysone (20E) titer at the prepupal stage was also suppressed, indicating that pseudogerm disrupts the ecdysteroid level by causing PG cell degeneration. Additionally, there was a suppression of Broad Complex (Br-C) expression in O. furnacalis larvae before the prepupal stage due to pseudogerms transplantation. When OfBr-C was knocked down by RNA-interference or knocked out by CRISPR/Cas9, approximately 24% and 48.3% of O. furnacalis larvae failed to pupate, respectively.

CONCLUSION

Pseudogerm potentially disrupts the 20E titer by destroying the host's PG and further inhibits the expression of OfBr-C, ultimately preventing host pupation. This study provides new insights into the strategies employed by parasitoids in controlling host development. © 2024 Society of Chemical Industry.

Differential regulation of reproduction and molting by juvenile hormone in aphids

Insects rely on juvenile hormones to regulate various physiological processes, including reproduction and molting; currently eight forms of this hormone are known. In most insects, only JH Ⅲ is synthesized. Meanwhile, aphids produce JH Ⅲ and JH Ⅲ skipped bisepoxide (JHSB3). However, it remains unclear whether these compounds play distinct roles in functional regulation. In this study, we demonstrated that the tested concentrations of JH Ⅲ effectively increased the number of aphid offspring, whereas high concentrations of JHSB3 affected the molting process. Drip experiments showed that 10 mg/L JH Ⅲ increased the number of offspring from 39.38 ± 8.03 to 56.50 ± 13.17, whereas 10 mg/L JHSB3 resulted in a 60.00 %± 5.77 % failure rate in molting before adulthood. Transcriptomic analysis also revealed that in the JH Ⅲ treatment group, 9 genes and 7 pathways associated with reproduction were expressed, but not genes or pathways associated with molting. In addition, 16 genes and 9 pathways associated with molting as well as 5 genes and 4 pathways associated with reproduction were identified in the JHSB3 treatment group. JH Ⅲ promotes reproduction in aphids by enhancing Vg expression, whereas JHSB3 affects molting by inhibiting the synthesis of molting hormone-related enzymes. The results indicate that JH Ⅲ and JHSB3 exhibit diverse functions in Aphis craccivora. The findings have significant implications for further studies on the physiological functions of different JHs.

The Dangers of Growing Old: Adult Moths Face Higher Predation Pressures than Caterpillars in Hyles lineata

Holometabolous insects display drastically different morphologies across life stages (i.e., larvae vs. adults). Morphological differences across life stages, such as different sizes and coloration, likely result in differential survival, as predators may find individuals of one life stage more conspicuous and/or more energetically profitable than another. Furthermore, prey conspicuousness may vary temporally because both the sensory environment and predator sensory abilities differ between day and night. Here, we investigated how the interaction between life stage (caterpillar vs. moth) and time of day (day vs. night) influences predation of the white-lined sphinx (Lepidoptera: Hyles lineata). We predicted that caterpillars would be less susceptible to predation than adult moths, as adults are larger and have a more conspicuous shape. After quantifying predation for 72 h during dawn and dusk using 199 plasticine replicas each of adults and caterpillars, predation on adult replicas was twice that of predation on caterpillar replicas. Furthermore, replicas were six times more likely to be predated on during the day than during the night. Lastly, attacks were made mainly by birds, which carried out 86% of the attacks on adult models and 85% of those on caterpillar models. These data support the hypothesis that predation rates differ across life stages in holometabolous insects. This research lays a foundation for further investigation into how specific differences in morphology across life stages affect predation and survival in holometabolous insects.

Interactions of juvenile hormone, 20-hydroxyecdysone, developmental genes, and miRNAs during pupal development in Apis mellifera

Insect development is primarily controlled by juvenile hormone (JH) and 20-hydroxyecdysone (20E), which regulate gene cascades leading to changes in phenotype, physiology, and behavior. Besides these hormones, microRNAs play a crucial role in insect development by regulating gene expression at the post-transcriptional level. To advance the molecular understanding of holometabolous developmental events, we investigate the pupal phase in the honeybee, Apis mellifera. In this study, we assessed the expression profiles of genes components of JH and 20E cascades - Usp, ftz-f1, EcR, Met, Chd64, InR-2, Kr-h1 and Tai - as well as the microRNAs miRNA-34 and miRNA-281 during pupal development of A. mellifera. We then analyzed the impact of JH and 20E treatments on the expression of these developmental genes and their putative regulators, the microRNAs. Overall, the selected genes and miRNAs remained stable or were downregulated following 20E treatment, while treatments with JH, upregulated most of our candidate developmental genes and microRNAs. Notably, the expression profile of Met, an intracellular receptor of JH, showed a strong correlation with fluctuations in 20E titers during pupal development. Furthermore, a computational analysis, followed by experimental assays, points to both miR-34 and miR-281 as potential regulators of pupal development in A. mellifera. This study paves the way for a better understanding of how JH and 20E hormones interact with developmental genes and microRNAs (miR-34 and miR-281) to regulate pupal development in honeybees, elucidating a piece of this complex network of interactions.

Krüppel homolog 1, a juvenile hormone transcription factor, regulates the reproduction and development of Aedes albopictus(Skuse) (Diptera: Culicidae)

The control of Aedes albopictus (Skuse) (Diptera: Culicidae), a vector for several important viral diseases, is crucial for mitigating mosquito-borne diseases. This study focused on the Krüppel homolog 1 (Kr-h1) gene, a transcription factor in juvenile hormone (JH) signaling, which plays a pivotal role in inhibiting metamorphosis and promoting adult reproduction. We characterized Aedes albopictus Kr-h1(AalbKr-h1), identified its eight zinc finger domains, and confirmed its orthology among insects through phylogenetic analysis. Expression profiling across life stages showed high level of expression in eggs, late larvae, and adults, with minimal expression in pupae. In adults, AalbKr-h1 was most active in the fat body and ovaries. Exposing larvae to a JH analogue significantly upregulated AalbKr-h1 expression in both larval and adult stages. RNAi-mediated knockdown of Kr-h1 protein reduced egg reproduction, survival rate and gene expression levels. These results provide a solid foundation for further exploration of the function of the AalbKr-h1 gene and the potential development of novel strategies for mosquito control and prevention of mosquito-borne diseases.

Insect Flight and Lipid Metabolism: Beyond the Classic Knowledge

Insects are the most successful animal group by various ecological and evolutionary metrics, including species count, adaptation diversity, biomass, and environmental influence. This book delves into the underlying reasons behind insects' dominance on Earth. Lipids play pivotal roles in insect biology, serving as fuel for physiological processes, signaling molecules, and structural components of biomembranes and providing waterproofing against dehydration, among other functions. The study of insect flight has been instrumental in advancing our understanding of insect metabolism, with the migratory locust (Locusta migratoria) and the tobacco hornworm (Manduca sexta) serving as prominent models. Throughout the 1980s and 1990s, numerous studies shed light on the role of adipokinetic hormone (AKH), a crucial neuropeptide in lipid mobilization, to support the extraordinary energy demands of insect flight. Remarkably, AKH was the first identified peptide hormone in insects. These pioneering works linking lipids and flight laid the groundwork for subsequent research characterizing the physiological roles of other neuroendocrine factors in energy substrate mobilization across diverse insect species. However, in the omics era, one may be surprised by the limited understanding of the complex cascade of events governing lipid supply to insect flight muscles. Thus, this chapter aims to provide a concise overview of the evolutionary significance of insect flight, emphasizing key advancements that expand our classical knowledge in this field. Ultimately, we hope this chapter serves as a modest tribute to the pioneering researchers of one of the most captivating areas in insect biology, inspiring further exploration into the myriad roles of lipids in insect biology.

Receptor tyrosine kinases CAD96CA and FGFR1 function as the cell membrane receptors of insect juvenile hormone

Juvenile hormone (JH) is important to maintain insect larval status; however, its cell membrane receptor has not been identified. Using the lepidopteran insect Helicoverpa armigera (cotton bollworm), a serious agricultural pest, as a model, we determined that receptor tyrosine kinases (RTKs) cadherin 96ca (CAD96CA) and fibroblast growth factor receptor homologue (FGFR1) function as JH cell membrane receptors by their roles in JH-regulated gene expression, larval status maintaining, rapid intracellular calcium increase, phosphorylation of JH intracellular receptor MET1 and cofactor Taiman, and high affinity to JH III. Gene knockout of Cad96ca and Fgfr1 by CRISPR/Cas9 in embryo and knockdown in various insect cells, and overexpression of CAD96CA and FGFR1 in mammalian HEK-293T cells all supported CAD96CA and FGFR1 transmitting JH signal as JH cell membrane receptors.

Insect metamorphosis and chitin metabolism under miRNA regulation: a review with current advances

Insect metamorphosis is a complex developmental process regulated by microRNAs (miRNAs) and hormonal signaling pathways. Key genes driving insect ontogenic changes are precisely modulated by miRNAs, which interact with 20-hydroxyecdysone (20E) and juvenile hormone (JH) to coordinate developmental transitions. Over the past decade, significant progress has been made in understanding miRNA biogenesis, their regulatory roles in gene expression, and their involvement in critical biological processes, including metamorphosis and chitin metabolism. miRNAs are now recognized as essential regulators of chitin metabolism and hormonal signaling, ensuring precise control of insect development. Disrupting the expression of participating genes in hormone signaling pathways through miRNAs leads to aberrant metamorphosis and consequent lethal outcomes, highlighting their potential as targets for pest control. This review summarizes current advances in miRNA-mediated regulation of insect metamorphosis and chitin metabolism, with a focus on their interactions with 20E and JH signaling pathways. By integrating recent findings, we provide insights into the molecular mechanisms underlying miRNA function in developmental transitions and their potential applications in insect pest management strategies. © 2025 Society of Chemical Industry.

Effects of Feeding Sources and Different Temperature Changes on the Gut Microbiome Structure of Chrysomya megacephala (Diptera: Calliphoridae)

Chrysomya megacephala (Diptera: Calliphoridae), commonly referred to as the oriental latrine fly, is a synanthropic blowfly species frequently associated with decomposing organic matter. This study sought to investigate the influence of various feeding substrates and temperature conditions, specifically constant temperatures of 15, 25, 35 °C, and variable temperatures averaging 23.31 °C, on the gut microbiome of C. megacephala. The microbiome analysis was conducted using the Illumina HiSeq platform for 16S rRNA gene sequencing in Changsha, China. Across all experimental conditions, the gut microbiome of C. megacephala yielded 1257 operational taxonomic units (OTUs), which were categorized into 26 phyla, 72 classes, 165 orders, 270 families, 516 genera, and 794 species. The study showed significant differences in the gut microbiome of C. megacephala between different feeding sources and temperature conditions across the lifespan. Low temperature had the potential to reduce the proportion abundance of bacterial communities in the gut microbiome, while high and variable temperature increased them. Metabolism was the main predicted function with diverse phenotypic characters in the gut microbiota of C. megacephala. The presence of diverse bacterial phenotypes in the gut microbiome of C. megacephala highlights its significant interest for medicine and offers promising applications in industry and agriculture.

Effects of larval foam-making and prolonged terrestriality on morphology, nitrogen excretion and development to metamorphosis in a Leptodactylid frog

At ontogenetic transitions, animals often exhibit plastic variation in development, behavior and physiology in response to environmental conditions. Most terrestrial-breeding frogs have aquatic larval periods. Some species can extend their initial terrestrial period, as either a plastic embryonic response to balance trade-offs across environments or an enforced wait for rain that allows larvae to access aquatic habitats. Terrestrial larvae of the foam-nesting frog, Leptodactylus fragilis, can arrest development, make their own nest foam to prevent dehydration, and synthesize urea to avoid ammonia toxicity. These plastic responses enable survival during unpredictably long periods in underground nest chambers, waiting for floods to enable exit and continued development in water. However, such physiological and behavioral responses may have immediate and long-term carry-over effects across subsequent ecological and developmental transitions. We examined effects of prolonged terrestriality and larval foam-making activity on larval physiology, development, and metamorphosis in L. fragilis. We tested for changes in foam-making ability by measuring the nests larvae produced following complete removal of parental foam at different ages. We measured ammonia and urea levels in larval foam nests to assess nitrogen excretion patterns, testing for effects of larval age, soil hydration around parental nests, and repeated nest construction. We also assessed immediate and long-term effects of larval foam-making and prolonged terrestriality on larval morphology at water entry and development to metamorphosis. We found that larvae arrested development during prolonged time on land and even young larvae were able to effectively produce multiple foam nests. We found high ammonia concentrations in larval nests, very high urea excretion by developmentally arrested older larvae, and faster growth of larvae in water than while constructing nests. Nonetheless, sibling larvae had a similar aquatic larval period and size at metamorphosis, regardless of their nest-making activity and timing of water entry. Sibship size increased the size of larval foam nests, but reduced per-capita foam production and increased size at metamorphosis, suggesting maternal effects in cooperative groups. Metamorph size also decreased with aquatic larval period. Our results highlight the extent of larval ability to maintain and construct a suitable developmental environment and excrete N-waste as urea, which are both crucial for survival during enforced extensions of terrestriality. Our results suggest that the energetic reserves in large eggs are sufficient to meet metabolic costs of urea synthesis and foam production during developmental arrest over an extended period on land, with no apparent carry-over effects on fitness-relevant traits at metamorphosis.

Increased versatility and convenience: Advances and strategy optimization of Receptor-Mediated Ovary Transduction of Cargo-mediated genetic modification in insects

Genetic modification via gene editing has become a widely adopted and demonstrably effective method in functional gene research within entomology. However, the optimal efficiency and simplicity of delivering exogenous guide RNA-clustered regularly interspaced short palindromic repeats-associated protein 9 complexes into target tissues are crucial for successful gene editing. The Receptor-Mediated Ovary Transduction of Cargo (ReMOT) strategy, which simplifies the delivery process, target-site selection, technical requirements, and delivery cost compared with embryonic microinjection, enabling efficient editing at the germline level, is gaining increasing attention. Although the feasibility and advantages of this technique have been demonstrated in various insect species, further optimization of operational details and the overcoming of further bottlenecks are still required. This review focuses on advances in developing ReMOT as a valuable technology, exploring its applicability, rationale for selecting the ovary as a delivery target site, factors influencing its efficiency, and improvement recommendations. The versatility and effectiveness of ReMOT make it a promising method for researchers looking to make precise genetic modifications with greater ease and efficiency.

Epigenetic processes in insect adaptation to environmental stress

Insects exhibit remarkable adaptability to a wide range of environmental stressors, including temperature fluctuations, pathogens, and changes in diet. This adaptability is often driven by epigenetic processes, which regulate gene expression without altering the underlying DNA sequence. This review provides a comprehensive overview of these epigenetic processes in insect adaptation, highlighting their impact on development, behaviour, and stress resilience. Understanding these mechanisms is essential for pest management and conservation efforts, offering insights into the rapid adaptive capacity of insects. By examining recent studies on epigenetics in insects, we aim to elucidate the molecular underpinnings of their adaptation and suggest future research directions in this evolving field.

Evolution of insect metamorphosis - an update

Metamorphosis endowed the insects with properties that enabled them to conquer the Earth. It is a hormonally controlled morphogenetic process that transforms the larva into the adult. Metamorphosis appeared with the origin of wings and flight. The sesquiterpenoid juvenile hormone (JH) suppresses wing morphogenesis and ensures that metamorphosis takes place at the right ontogenetic time. This review explores the origin of insect metamorphosis and the ancestral function of JH. Fossil record shows that the first Paleozoic winged insects had (hemimetabolous) metamorphosis, and their larvae were likely aquatic. In the primitive wingless silverfish that lacks metamorphosis, JH is essential for late embryogenesis and reproduction. JH production after the embryo dorsal closure promotes hatching and terminal tissue maturation.

Kin Competition Drives the Evolution of Earlier Metamorphosis

Metamorphosis, the discrete morphological change between postembryonic life stages, is widespread across the animal kingdom. The suggested advantages of metamorphosis have usually been framed in terms of population benefits, i.e., ecological explanations. In contrast, evolutionary explanations concern whether and how metamorphosis spreads through a population owing to individual-fitness benefits. However, how kin selection modulates evolution of metamorphosis remains to be investigated formally. Here we develop a mathematical model to investigate how kin selection shapes the optimal timing of metamorphosis from foraging, non-reproductive larva to reproductive adult, when larvae tend to cluster with their genetic relatives. We consider the full range of larval competition intensities-from no competition to full competition-and the full range of relatedness coefficients-from unrelated to clonality. We provide testable predictions as to how kin selection modulates the timing of metamorphosis, as well as a conceptual framework within which empirical observations may be understood.

The steroid hormone 20-hydroxyecdysone inhibits RAPTOR expression by repressing Hox gene transcription to induce autophagy

Regulatory-associated protein of TOR (RAPTOR) is a key component of TOR complex 1, which determines the lysosomal location and substrate recruitment of TOR complex 1 to promote cell growth and prevent autophagy. Many studies in recent decades have focused on the post-translational modification of RAPTOR; however, little is known about the transcriptional regulatory mechanism of Raptor. Using the lepidopteran insect cotton bollworm (Helicoverpa armigera) as model, we reveal the transcriptional regulatory mechanism of Raptor. RAPTOR has different expression profiles in tissues during development from larva to late pupa, with high expression levels at larval feeding stages but low expression levels during metamorphic stages in the epidermis, midgut, and fat body. RAPTOR is localized in the larval midgut at the feeding stage but is localized in the imaginal midgut at metamorphic stages. The knockdown of Raptor at the feeding stage results in the production of small pupae, early autophagy of the midgut and fat body, and decreased cell proliferation. However, Raptor knockdown at metamorphic stage represses the development of the epidermis, adult fat body, and brain. 20-Hydroxecdysone (20E) represses Raptor transcription. Homeobox (HOX) proteins promote Raptor transcription by binding to its promoter. Overexpression of HOX proteins represses autophagy-related gene expression and autophagy but increases cell proliferation. 20E represses Hox genes transcription via its nuclear receptor EcR binding to its promoters. Together, these findings suggest that HOX proteins are positive regulators that upregulate Raptor transcription. 20E represses Hox gene transcription, thus repressing Raptor expression, resulting in autophagy and repressing cell proliferation during metamorphosis.

Evolutionary Novelty of Apolipoprotein D Facilitates Metabolic Plasticity in Lepidopteran Wings

Understanding metabolic plasticity of animal evolution is a fundamental challenge in evolutionary biology. Owing to the diversification of insect wing morphology and dynamic energy requirements, the molecular adaptation mechanisms underlying the metabolic pathways in wing evolution remain largely unknown. This study reveals the pivotal role of the duplicated Apolipoprotein D (ApoD) gene in lipid and energy homeostasis in the lepidopteran wing. ApoD underwent significant expansion in insects, with gene duplication and consistent retention observed in Lepidoptera. Notably, duplicated ApoD2 was highly expressed in lepidopteran wings and encoded a unique C-terminal tail, conferring distinct ligand-binding properties. Using Bombyx mori as a model organism, we integrated evolutionary analysis, multiomics, and in vivo functional experiments to elucidate the way duplicated ApoD2 mediates lipid trafficking and homeostasis via the AMP-activated protein kinase pathway in wings. Moreover, we revealed the specific expression and functional divergence of duplicated ApoD as a key mechanism regulating lipid homeostasis in the lepidopteran wing. These findings highlight an evolutionary scenario in which neofunctionalization conferred a novel role of ApoD in shaping adaptive lipid metabolic regulatory networks during wing phenotypic evolution. Overall, we provide in vivo evidence for the functional differentiation of duplicate genes in shaping adaptive metabolic regulatory networks during phenotypic evolution.

Comparative genomics reveals carbohydrate enzymatic fluctuations and herbivorous adaptations in arthropods

Background

Arthropods represent the largest and most diverse phylum on Earth, playing a pivotal role in the biosphere. One key to their evolutionary success is their ability to feed on plant material. However, their endogenous enzymatic repertoire, which contributes to plant digestion, remains largely unexplored and poorly understood.

Results

We analyzed 815 arthropod proteomes and identified a total of 268,171 carbohydrate-active modules. Our findings revealed a strong correlation between enzymatic content and feeding habits, with herbivorous species possessing significantly higher enzyme levels. We identified widespread carbohydrate-active families across the AA, CBM, GH, and GT classes, and observed a progressive increase in taxa-exclusive families in more recent arthropod lineages. Notably, we highlighted the impact of the transition from ametabolous to holometabolous development on carbohydrate metabolism, as well as the ecological adaptations of different species groups. By reconstructing the ancestral enzymatic profiles of arthropods, we identified significant fluctuations in 10 carbohydrate-active families over time.

Conclusions

Our analysis advances the understanding of the evolutionary mechanisms utilized by the megadiverse phylum Arthropoda. We emphasize the critical role of herbivory as a selective force shaping enzymatic strategies, particularly those involved in carbohydrate metabolism. The distribution and exclusivity of carbohydrate-active families across different arthropod groups provide insights into their evolutionary trajectories and offer a clearer picture of the metabolic pathways that led their ancestors to their present forms.

A critical role for the nuclear protein Akirin in larval development in Henosepilachna vigintioctopunctata

Akirin is a nuclear protein that controls development in vertebrates and invertebrates. The function of Akirin has not been assessed in any Coleopteran insects. We found that high levels of akirin transcripts in Henosepilachna vigintioctopunctata, a serious Coleopteran potato defoliator (hereafter Hvakirin), were present at prepupal, pupal and adult stages, especially in larval foregut and fat body. RNA interference (RNAi) targeting Hvakirin impaired larval development. The Hvakirin RNAi larvae arrested development at the final larval instar stage. They remained as stunted larvae, gradually blackened and finally died. Moreover, the remodelling of gut and fat body was inhibited in the Hvakirin depleted larvae. Two layers of cuticles, old and newly formed, were noted in the dsegfp-injected animals. In contrast, only a layer of cuticle was found in the dsakirin-injected beetles, indicating the arrest of larval development. Furthermore, the expression of three transforming growth factor-β cascade genes (Hvsmox, Hvmyo and Hvbabo), a 20-hydroxyecdysone (20E) receptor gene (HvEcR) and six 20E response genes (HvHR3, HvHR4, HvE75, HvBrC, HvE93 and Hvftz-f1) was significantly repressed, consistent with decreased 20E signalling. Conversely, the transcription of a juvenile hormone (JH) biosynthesis gene (Hvjhamt), a JH receptor gene (HvMet) and two JH response genes (HvKr-h1 and HvHairy) was greatly enhanced. Our findings suggest a critical role of Akirin in larval development in H. vigintioctopunctata.

Juvenile hormone-induced microRNA miR-iab-8 regulates lipid homeostasis and metamorphosis in Drosophila melanogaster

Metamorphosis plays an important role in the evolutionary success of insects. Accumulating evidence indicated that microRNAs (miRNAs) are involved in the regulation of processes associated with insect metamorphosis. However, the miRNAs coordinated with juvenile hormone (JH)-regulated metamorphosis remain poorly reported. In the present study, using high-throughput miRNA sequencing combined with Drosophila genetic approaches, we demonstrated that miR-iab-8, which primarily targets homeotic genes to modulate haltere-wing transformation and sterility was up-regulated by JH and involved in JH-mediated metamorphosis. Overexpression of miR-iab-8 in the fat body resulted in delayed development and failure of larval-pupal transition. Furthermore, metabolomic analysis results revealed that overexpression of miR-iab-8 caused severe energy metabolism defects especially the lipid metabolism, resulting in significantly reduced triacylglycerol (TG) content and glycerophospholipids but enhanced accumulation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In line with this, Nile red staining demonstrated that during the third larval development, the TG content in the miR-iab-8 overexpression larvae was continuously decreased, which is opposite to the control. Additionally, the transcription levels of genes committed to TG synthesis and breakdown were found to be significantly increased and the expression of genes responsible for glycerophospholipids metabolism were also altered. Overall, we proposed that JH induced miR-iab-8 expression to perturb the lipid metabolism homeostasis especially the TG storage in the fat body, which in turn affected larval growth and metamorphosis.

The moulting arthropod: a complete genetic toolkit review

Exoskeletons are a defining character of all arthropods that provide physical support for their segmented bodies and appendages as well as protection from the environment and predation. This ubiquitous yet evolutionarily variable feature has been instrumental in facilitating the adoption of a variety of lifestyles and the exploitation of ecological niches across all environments. Throughout the radiation that produced the more than one million described modern species, adaptability afforded by segmentation and exoskeletons has led to a diversity that is unrivalled amongst animals. However, because of the limited extensibility of exoskeleton chitin and cuticle components, they must be periodically shed and replaced with new larger ones, notably to accommodate the growing individuals encased within. Therefore, arthropods grow discontinuously by undergoing periodic moulting events, which follow a series of steps from the preparatory pre-moult phase to ecdysis itself and post-moult maturation of new exoskeletons. Each event represents a particularly vulnerable period in an arthropod's life cycle, so processes must be tightly regulated and meticulously executed to ensure successful transitions for normal growth and development. Decades of research in representative arthropods provide a foundation of understanding of the mechanisms involved. Building on this, studies continue to develop and test hypotheses on the presence and function of molecular components, including neuropeptides, hormones, and receptors, as well as the so-called early, late, and fate genes, across arthropod diversity. Here, we review the literature to develop a comprehensive overview of the status of accumulated knowledge of the genetic toolkit governing arthropod moulting. From biosynthesis and regulation of ecdysteroid and sesquiterpenoid hormones, to factors involved in hormonal stimulation responses and exoskeleton remodelling, we identify commonalities and differences, as well as highlighting major knowledge gaps, across arthropod groups. We examine the available evidence supporting current models of how components operate together to prepare for, execute, and recover from ecdysis, comparing reports from Chelicerata, Myriapoda, Crustacea, and Hexapoda. Evidence is generally highly taxonomically imbalanced, with most reports based on insect study systems. Biases are also evident in research on different moulting phases and processes, with the early triggers and late effectors generally being the least well explored. Our synthesis contrasts knowledge based on reported observations with reasonably plausible assumptions given current taxonomic sampling, and exposes weak assumptions or major gaps that need addressing. Encouragingly, advances in genomics are driving a diversification of tractable study systems by facilitating the cataloguing of putative genetic toolkits in previously under-explored taxa. Analysis of genome and transcriptome data supported by experimental investigations have validated the presence of an "ultra-conserved" core of arthropod genes involved in moulting processes. The molecular machinery has likely evolved with elaborations on this conserved pathway backbone, but more taxonomic exploration is needed to characterise lineage-specific changes and novelties. Furthermore, linking these to transformative innovations in moulting processes across Arthropoda remains hampered by knowledge gaps and hypotheses based on untested assumptions. Promisingly however, emerging from the synthesis is a framework that highlights research avenues from the underlying genetics to the dynamic molecular biology through to the complex physiology of moulting.

Replacement of fish meal with full fat Hermetia illucens modulates hepatic FXR signaling in juvenile rainbow trout (Oncorhynchus mykiss): Exploring a potential role of ecdysteroids

The present study was conducted to investigate the effects of fish meal (FM) replacement with full fat Hermetia illucens (HI) on the molecular mechanisms regulating lipid and bile salt (BA) homeostasis in rainbow trout (Oncorhynchus mykiss) juveniles. We thus explore the presence of 20-hydroxyecdysone (20E) in an insect meal-based diet and evaluate its potential involvement in regulating the molecular mechanisms/basis of FXR:RXR axis signaling. Ecdysteroids are a category of steroid hormones which bind a nuclear-receptor complex composed of ecdysone receptor (EcR) and ultraspiracle protein (USP) and regulate insect molting and metamorphosis. In all vertebrates, including fish, EcR-USP homologs are the Farnesoid X receptors (FXR) and the Retinoid X receptors (RXR), which are known to regulate crucial physiological and metabolic aspects, including BA synthesis and cholesterol homeostasis. In silico prediction indicates that 20E binds the heterodimeric complex with a binding affinity constant Kd equals to 610 ± 60 nM and affects positively the dimerization process. Results also demonstrated the coordinated increased expression of FXR and RXR, as well as their downstream target genes (i.e. short heterodimer partner 1 and 2) in rainbow trout fed diets containing HI meal. This latter finding was paralleled by a significant down-regulation of CYP7a1 and CYP8b1 gene expression together with a decrease in hepatic total cholesterol, triglyceride, and BA levels. Overall, our study suggested that FXR is a potential target for 20E content in insect meal and provided preliminary data on the potential role of ecdysteroids in regulating the metabolic status of teleost fish through modulation of FXR signaling in the enterohepatic system.

Acquisition of polymorphism in the chordate doliolids

In polymorphic organisms, a single genome is deployed to program numerous, morphologically distinct body plans within a colony. This complex life history trait has evolved independently within a limited subset of animal taxa. Reconstructing the underlying genetic, cellular, and developmental changes that drove the emergence of polymorphic colonies represents a promising avenue for exploring diversifying selection and resulting impacts on developmental gene regulatory networks. Doliolids are the only polymorphic chordate, deploying a single genome to program distinct morphs specialized for locomotion, feeding, asexual, or sexual reproduction. In this review, we provide a detailed summary of doliolid anatomy, development, taxonomy, ecology, life history, and the cellular basis for doliolid polymorphism. In order to frame the potential evolutionary and developmental insights that could be gained by studying doliolids, we provide a broader overview of polymorphism. We then discuss how comparative studies of polymorphic cnidarians have begun to illuminate the genetic basis of this unusual and complex life history strategy. We then provide a summary of life history divergence in the chordates, particularly among doliolids and their polymorphic cousins, the salps and pyrosomes.

Stem cell-specific ecdysone signaling regulates the development of dorsal fan-shaped body neurons and sleep homeostasis

Complex behaviors arise from neural circuits that assemble from diverse cell types. Sleep is a conserved behavior essential for survival, yet little is known about how the nervous system generates neuron types of a sleep-wake circuit. Here, we focus on the specification of Drosophila 23E10-labeled dorsal fan-shaped body (dFB) long-field tangential input neurons that project to the dorsal layers of the fan-shaped body neuropil in the central complex. We use lineage analysis and genetic birth dating to identify two bilateral type II neural stem cells (NSCs) that generate 23E10 dFB neurons. We show that adult 23E10 dFB neurons express ecdysone-induced protein 93 (E93) and that loss of ecdysone signaling or E93 in type II NSCs results in their misspecification. Finally, we show that E93 knockdown in type II NSCs impairs adult sleep behavior. Our results provide insight into how extrinsic hormonal signaling acts on NSCs to generate the neuronal diversity required for adult sleep behavior. These findings suggest that some adult sleep disorders might derive from defects in stem cell-specific temporal neurodevelopmental programs.

CYP303A1 regulates molting and metamorphosis through 20E signaling in Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Cytochrome P450s play a crucial role in the breakdown of external substances and perform important activities in the hormone system of insects. It has been understood that P450s were essential in the metabolism of ecdysteroids. CYP303A1 is a highly conserved CYP in most insects, but its specific physiological functions remain poorly understood in Nilaparvata lugens Stål. In this study, NlCYP303A1 was identified and highly expressed in the pre-molt stages, predominantly in the cuticle-producing tissues. Silencing of NlCYP303A1 caused a lethal phenotype with a molting defect. Moreover, the 20E titers, the expression levels of Halloween genes, and critical genes associated with the 20E signaling pathway in N. lugens nymphs were significantly decreased with the silencing NlCYP303A1. We further performed additional backfilling of 20E to rescue the RNAi effects on NlCYP303A1. The gene expression levels that were previously reduced caused by silencing NlCYP303A1 were significantly elevated. However, the molting defects of nymphs were not effectively improved. The results demonstrated NlCYP303A1 plays a crucial role in the molting and metamorphosis of N. lugens by regulating the 20E signaling pathway and cuticular formation, enhances the understanding of the functional role of CYP 2 clans, and identifies candidate gene for RNAi-based control of N. lugens.

Viral- and fungal-mediated behavioral manipulation of hosts: summit disease

Summit disease, in which infected hosts seek heights (gravitropism), first noted in modern times by nineteenth-century naturalists, has been shown to be induced by disparate pathogens ranging from viruses to fungi. Infection results in dramatic changes in normal activity patterns, and such parasite manipulation of host behaviors suggests a strong selection for convergent outcomes albeit evolved via widely divergent mechanisms. The two best-studied examples involve a subset of viral and fungal pathogens of insects that induce "summiting" in infected hosts. Summiting presumably functions as a means for increasing the dispersal of the pathogen, thus significantly increasing fitness. Here, we review current advances in our understanding of viral- and fungal-induced summit disease and the host behavioral manipulation involved. Viral genes implicated in this process include a host hormone-targeting ecdysteroid UDP-glucosyltransferase (apparently essential for mediating summit disease induced by some viruses but not all) and a protein tyrosine phosphatase, with light dependance implicated. For summit disease-causing fungi, though much remains obscure, targeting of molting, circadian rhythms, sleep, and responses to light patterns appear involved. Targeting of host neuronal pathways by summit-inducing fungi also appears to involve the production of effector molecules and secondary metabolites that affect host muscular, immune, and/or neurological processes. It is hypothesized that host brain structures, particularly Mushroom Bodies (no relation to the fungus itself), important for olfactory association learning and control of locomotor activity, are critical targets for mediating summiting during infection. This phenomenon expands the diversity of microbial pathogen-interactions and host dynamics. KEY POINTS: • Summit disease or height seeking (gravitropism) results from viral and fungal pathogens manipulating insect host behaviors presumably to increase pathogen dispersal. • Insect baculoviruses and select fungal pathogens exhibit convergent evolution in host behavioral manipulation but use disparate molecular mechanisms. • Targets for affecting host behavior include manipulation of host hormones, feeding, locomotion, and immune, circadian, and neurological pathways.

Stability and suitability of housekeeping genes in phlebotomine sand flies

We investigated gene expression patterns in Lutzomyia and Phlebotomus sand fly vectors of leishmaniases. Using quantitative PCR, we assessed the expression stability of potential endogenous control genes commonly used in dipterans. We analyzed Lutzomyia longipalpis and Phlebotomus papatasi samples from L3 and L4 larval stages, adult sand flies of different sexes, diets, dsRNA injection, and Leishmania infection. Six genes were evaluated: actin, α-tubulin, GAPDH, 60 S ribosomal proteins L8 and L32 (RiboL8 and RiboL32), and elongation factor 1-α (EF1-α). EF1-α was among the most stably expressed along with RiboL8 in L. longipalpis larvae and RiboL32 in adults. In P. papatasi, EF1-α and RiboL32 were the top in larvae, while EF1-α and actin were the most stable in adults. RiboL8 and actin were the most stable genes in dissected tissues and infected guts. Additionally, five primer pairs designed for L. longipalpis or P. papatasi were effective in PCR with Lutzomyia migonei, Phlebotomus duboscqi, Phlebotomus perniciosus, and Sergentomyia schwetzi cDNA. Furthermore, L. longipalpis RiboL32 and P. papatasi α-tubulin primers were suitable for qPCR with cDNA from the other four species. Our research provides tools to enhance relative gene expression studies in sand flies, facilitating the selection of endogenous control for qPCR.

Soul is a master control gene governing the development of the Drosophila prothoracic gland

The prothoracic gland (PG) is a major insect endocrine organ. It is the principal source of insect steroid hormones, and critical for key developmental events such as the molts, the establishment of critical weight (CW), pupation, and sexual maturation. However, little is known about the developmental processes that regulate PG morphology. In this study, we identified soul, which encodes a PG-specific basic helix-loop-helix (bHLH) transcription factor. We demonstrate that Tap, also a bHLH protein, dimerizes with Soul. Both are expressed in the developing PG. Interfering with either soul or tap function caused strikingly similar phenotypes, resulting in small and fragmented PGs, the abolishment of steroid hormone-producing gene expression, larval arrest, and a failure to undergo metamorphosis. Furthermore, both soul and tap showed expression peaks just prior to the CW checkpoint. Disrupting soul- or tap-function before, but not after, the CW checkpoint caused larval arrest, and perturbed highly similar gene cohorts, which were enriched for regulators and components of the steroid hormone biosynthesis pathway. Intriguingly, a chitin-based cuticle gene, Cpr49Ah, and a POU domain transcription factor gene, pdm3, are direct target genes of the Soul/Tap complex, and disruption of either phenocopied key aspects of soul/tap loss-of-function phenotypes. Taken together, our findings demonstrate that the Soul/Tap heterodimer resides at the top of a complex gene hierarchy that drives PG development, CW establishment, and steroid hormone production.

Expression of a viral ecdysteroid UDP-glucosyltransferase enhanced the insecticidal activity of the insect pathogenic fungus Beauveria bassiana

BACKGROUND

Entomopathogenic fungi, such as Beauveria bassiana, hold promise as biological control agents against insect pests. However, the efficacy of these fungi can be hindered by insect immune responses. One strategy to enhance fungal virulence is to manipulate host immune by targeting key regulatory molecules like 20-hydroxyecdysone (20E).

RESULTS

In this study, we engineered B. bassiana strains to constitutively express the enzyme ecdysteroid UDP-glucosyltransferase (EGT), which inactivates 20E, a crucial insect molting hormone. The engineered strain Bb::EGT-1 exhibited robust expression of EGT, leading to a significant reduction in insect 20E levels upon infection. Moreover, infection with Bb::EGT-1 resulted in accelerated larval mortality. Immune responses analysis revealed repression of insect immune response genes and decreased phenoloxidase (PO) activity in larvae infected with Bb::EGT-1. Microbiome analysis indicated alterations in bacterial composition within infected insects, with increased abundance observed during infection with Bb::EGT-1. Additionally, the presence of bacteria hindered hyphal emergence from insect cadavers, suggesting a role for microbial competition in fungal dissemination.

CONCLUSIONS

Constitutive expression of EGT in B. bassiana enhances fungal virulence by reducing insect 20E levels, suppressing immune responses, and altering the insect microbiome. These findings highlighted the potential of engineered fungi as effective biocontrol agents against insect pests and provide insights into the complex interactions between entomopathogenic fungi, their hosts, and associated microbes. © 2024 Society of Chemical Industry.

Agonist-dependent action of the juvenile hormone receptor

Juvenile hormone (JH) signaling is realized at the gene regulatory level by receptors of the bHLH-PAS transcription factor family. The sesquiterpenoid hormones and their synthetic mimics are agonist ligands of a unique JH receptor (JHR) protein, methoprene-tolerant (MET). Upon binding an agonist to its PAS-B cavity, MET dissociates from a cytoplasmic chaperone complex including HSP83 and concomitantly switches to a bHLH-PAS partner taiman, forming a nuclear, transcriptionally active JHR heterodimer. This course of events resembles the vertebrate aryl hydrocarbon receptor (AHR), activated by a plethora of endogenous and synthetic compounds. Like in AHR, the pliable PAS-B cavity of MET adjusts to diverse ligands and binds them through similar mechanisms. Despite recent progress, we only begin to discern agonist-induced conformational shifts within the PAS-B domain, with the ultimate goal of understanding how these localized changes stimulate the assembly of the active JHR complex and, thus, fully grasp the mechanism of JHR signaling.

Juvenile hormone signal transducer hairy inhibits Krüppel homolog1 expression

Hairy and Krüppel homolog 1 (Kr-h1) are transcriptional repressors that act synergistically to mediate the gene-repressive action of juvenile hormone (JH). However, whether a regulatory relationship exists between Hairy and Kr-h1 remains unclear. In this study, an inhibitory effect of Hairy on Kr-h1 expression was found. Genetic studies in Drosophila have shown that the simultaneous overexpression of Hairy and Kr-h1 can rescue the defective phenotypes caused by the overexpression of a single factor. Reduced expression of Kr-h1 was observed in Hairy-overexpressing flies and cells, whereas the expression levels of Hairy were unaffected in cells with ectopic expression of Kr-h1. The inhibitory effect of Hairy on Kr-h1 expression was found to occur at the transcriptional level, as Hairy bound directly to the B-box within the Kr-h1 promoter via the bHLH motif and recruited the corepressors C-terminal binding protein (CtBP) and Groucho (Gro) through the PLSLV and WRPW motifs, respectively. Our findings revealed a regulatory relationship between two JH response factors, which advances our understanding of the molecular mechanism of JH signaling.

Rapid growth and the evolution of complete metamorphosis in insects

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.

Effects of molting on the expression of ecdysteroid responsive genes in the crustacean molting gland (Y-organ)

Ecdysteroid molting hormones coordinate arthropod growth and development. Binding of 20-hydroxyecdysone (20E) to ecdysteroid receptor EcR/RXR activates a cascade of nuclear receptor transcription factors that mediate tissue responses to hormone. Insect ecdysteroid responsive and Forkhead box class O (FOXO) transcription factor gene sequences were used to extract orthologs from blackback land crab (Gecarcinus lateralis) Y-organ (YO) transcriptome: Gl-Ecdysone Receptor (EcR), Gl-Broad Complex (Br-C), Gl-E74, Gl-Hormone Receptor 3 (HR3), Gl-Hormone Receptor 4 (HR4), Gl-FOXO, and Gl-Fushi tarazu factor-1 (Ftz-f1). Quantitative polymerase chain reaction quantified mRNA levels in tissues from intermolt animals and in YO of animals induced to molt by multiple limb autotomy (MLA) or eyestalk ablation (ESA). Gl-EcR, Gl-Retinoid X Receptor (RXR), Gl-Br-C, Gl-HR3, Gl-HR4, Gl-E74, Gl-E75, Gl-Ftz-f1, and Gl-FOXO were expressed in all 10 tissues, with Gl-Br-C, Gl-E74, Gl-E75, and Gl-HR4 mRNA levels in the YO lower than those in most of the other tissues. In MLA animals, molting had no effect on Gl-Br-C, Gl-E74, and Gl-Ftz-f1 mRNA levels and little effect on Gl-EcR, Gl-E75, and Gl-HR4 mRNA levels. Gl-HR3 and Gl-FOXO mRNA levels were increased during premolt stages, while Gl-RXR mRNA level was highest during intermolt and premolt stages and lowest at postmolt stage. In ESA animals, YO mRNA levels were not correlated with hemolymph ecdysteroid titers. ESA had no effect on Gl-EcR, Gl-E74, Gl-HR3, Gl-HR4, Gl-Ftz-f1, and Gl-FOXO mRNA levels, while Gl-RXR, Gl-Br-C, and Gl-E75 mRNA levels were decreased at 3 days post-ESA. These data suggest that transcriptional up-regulation of Gl-FOXO and Gl-HR3 contributes to increased YO ecdysteroidogenesis during premolt. By contrast, transcriptional regulation of ecdysteroid responsive genes and ecdysteroidogenesis were uncoupled in the YO of ESA animals.

The genetic determination of alternate stages in polyphenic insects

Molt-based transitions in form are a central feature of insect life that have enabled adaptation to diverse and changing environments. The endocrine regulation of these transitions is well established, but an understanding of their genetic regulation has only recently emerged from insect models. The pupal and adult stages of metamorphosing insects are determined by the stage specifying transcription factors broad-complex (br) and Ecdysone inducible protein 93 (E93), respectively. A probable larval determinant, chronologically inappropriate metamorphosis (chinmo), has just recently been characterized. Expression of these three transcription factors in the metamorphosing insects is regulated by juvenile hormone with ecdysteroid hormones, and by mutual repression between the stage-specific transcription factors. This review explores the hypothesis that variations in the onset, duration, and tissue-specific expression of chinmo, br, and E93 underlie other polyphenisms that have arisen throughout insects, including the castes of social insects, aquatic stages of mayflies, and the neoteny of endoparasites. The mechanisms that constrain how chinmo, br, and E93 expression may vary will also constrain the ways that insect life history may evolve. I find that four types of expression changes are associated with novel insect forms: (1) heterochronic shift in the turnover of expression, (2) expansion or contraction of expression, (3) tissue-specific expression, and (4) redeployment of stage-specific expression. While there is more to be learned about chinmo, br, and E93 function in diverse insect taxa, the studies outlined here show that insect stages are modular units in developmental time and a substrate for evolutionary forces to act upon.

The mlpt smORF gene is essential for digestive physiology and molting during nymphal stages in the kissing bug Rhodnius prolixus

Chagas disease affects around 8 million people globally, with Latin America bearing approximately 10,000 deaths each year. Combatting the disease relies heavily on vector control methods, necessitating the identification of new targets. Within insect genomes, genes harboring small open reading frames (smORFs - < 100 amino acids) present numerous potential candidates. In our investigation, we elucidate the pivotal role of the archetypal smORF-containing gene, mille-pattes/polished-rice/tarsalless (mlpt/pri/tal), in the post-embryonic development of the kissing bug Rhodnius prolixus. Injection of double-stranded RNA targeting mlpt (dsmlpt) during nymphal stages yields a spectrum of phenotypes hindering post-embryonic growth. Notably, fourth or fifth stage nymphs subjected to dsmlpt do not undergo molting. These dsmlpt nymphs display heightened mRNA levels of JHAMT-like and EPOX-like, enzymes putatively involved in the juvenile hormone (JH) pathway, alongside increased expression of the transcription factor Kr-h1, indicating changes in the hormonal control. Histological examination reveals structural alterations in the hindgut and external cuticle of dsmlpt nymphs compared to control (dsGFP) counterparts. Furthermore, significant changes in the vector's digestive physiology were observed, with elevated hemozoin and glucose levels in the posterior midgut of dsmlpt nymphs. Importantly, dsmlpt nymphs exhibit impaired metacyclogenesis of Trypanosoma cruzi, the causative agent of Chagas disease, underscoring the crucial role of proper gut organization in parasite differentiation. Thus, our findings constitute the first evidence of a smORF-containing gene's regulatory influence on vector physiology, parasitic cycle, and disease transmission.

New insights about the toxicity of 2,4-D: Gene expression analysis reveals modulation on several subcellular responses in Chironomus riparius

Herbicides are the main class of pesticides applied in crops and are capable of polluting the surrounding freshwater system; thus, understanding their impact on non-target species, whose mechanism of action is not described, helps to elucidate the real risks of these pollutants to the environment. 2,4-dichlorophenoxyacetic acid (2,4-D) is frequently detected in water and, due to its persistence, poses a risk to wildlife. In this way, the present work aimed to describe the implication of exposure to concentrations of 2,4-D already reported in aquatic environments in several physiological mechanisms of C. riparius at molecular and biochemical levels. To achieve this, bioassays were conducted with fourth instar larvae exposed to three concentrations of 2,4-D (0.1, 1.0, and 7.5 μg L-1). Larvae were collected after 24 and 96 h of exposure, and the expression of 42 genes, related to six subcellular mechanisms, was assessed by Real-Time PCR (RT-PCR). Besides, the activity of the enzymes catalase (CAT), glutathione S-transferase (GST), and acetylcholinesterase (AChE) was determined. The main metabolic route altered after exposure to 2,4-D was the endocrine system (mainly related to 20-hydroxyecdysone and juvenile hormone), confirming its endocrine disruptor potential. Four of the eleven stress response genes studied were down-regulated, and later exposure modulated DNA-repair genes suggesting genotoxic capacity. Moreover, only one gene from each detoxification phase was modulated at short exposure to 1.0 μg L-1. The molecular responses were not dose-dependent, and some early responses were not preserved after 96 h, indicating a transient response to the herbicide. Exposure to 2,4-D did not alter the activity of CAT, GST, and AChE enzymes. The responses described in this study reveal new mechanistic pathways of toxicity for 2,4-D in non-target organisms and highlight potential ecological consequences for chironomids in aquatic systems at the edges of agricultural fields.

The transcription factor RUNT-like regulates pupal cuticle development via promoting a pupal cuticle protein transcription

Holometabolous insects undergo morphological remodeling from larvae to pupae and to adults with typical changes in the cuticle; however, the mechanism is unclear. Using the lepidopteran agricultural insect Helicoverpa armigera, cotton bollworm, as a model, we revealed that the transcription factor RUNT-like (encoded by Runt-like) regulates the development of the pupal cuticle via promoting a pupal cuticle protein gene (HaPcp) expression. The HaPcp was highly expressed in the epidermis and wing during metamorphosis and was found being involved in pupal cuticle development by RNA interference (RNAi) analysis in larvae. Runt-like was also strongly upregulated in the epidermis and wing during metamorphosis. Knockdown of Runt-like produced similar phenomena, a failure of abdomen yellow envelope and wing formation, to those following HaPcp knockdown. The insect molting hormone 20-hydroxyecdysonen (20E) upregulated HaPcp transcription via RUNT-like. 20E upregulated Runt-like transcription via nuclear receptor EcR and the transcription factor FOXO. Together, RUNT-like and HaPCP are involved in pupal cuticle development during metamorphosis under 20E regulation.

Schlank orchestrates insect developmental transition by switching H3K27 acetylation to trimethylation in the prothoracic gland

Insect developmental transitions are precisely coordinated by ecdysone and juvenile hormone (JH). We previously revealed that accumulated H3K27 trimethylation (H3K27me3) at the locus encoding JH signal transducer Hairy is involved in the larval-pupal transition in insects, but the underlying mechanism remains to be fully defined. Here, we show in Drosophila and Bombyx that Rpd3-mediated H3K27 deacetylation in the prothoracic gland during the last larval instar promotes ecdysone biosynthesis and the larval-pupal transition by enabling H3K27me3 accumulation at the Hairy locus to induce its transcriptional repression. Importantly, we find that the homeodomain transcription factor Schlank acts to switch active H3K27 acetylation (H3K27ac) to repressive H3K27me3 at the Hairy locus by directly binding to the Hairy promoter and then recruiting the histone deacetylase Rpd3 and the histone methyltransferase PRC2 component Su(z)12 through physical interactions. Moreover, Schlank inhibits Hairy transcription to facilitate the larval-pupal transition, and the Schlank signaling cascade is suppressed by JH but regulated in a positive feedback manner by ecdysone. Together, our data uncover that Schlank mediates epigenetic reprogramming of H3K27 modifications in hormone actions during insect developmental transition.

Efficient CRISPR/Cas9-mediated ebony gene editing in the greater wax moth Galleria mellonella

The greater wax moth, Galleria mellonella (Lepidoptera, Pyralidae), is a major bee pest that inflicts considerable harm on beehives, leading to economic losses. It also serves as a valuable resource insect and a model organism. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system plays a crucial role in improving economic insect breeding and developing efficient agricultural pest management systems in Lepidoptera. However, the CRISPR/Cas9 protocols have not been developed for G. mellonella. Here, the Gmebony knockout (KO) strain was established using the CRISPR/Cas9 genome editing system. We obtained Gmebony KO strain in the G4 generation, which took approximately 10 months. When compared with wild-type, the head, notum, and the terminal abdominal surface of 1st to 4th instar larvae in the KO strain changed from yellow to brown, and these regions of the KO strain gradually transformed into a black color from the 5th instar larvae, and the body color of the adult moth in the KO strain changed to black. The developmental period of the early larval and the following larval instars extended. The embryonic hatchability of the Gmebony KO strain was significantly decreased. The pupal body weight of the Gmebony KO strain was not affected. The feasibility of the CRISPR/Cas9 methodology was validated by single-target editing of Gmebony. Our findings provide the first evidence that the ebony gene can serve as a pigmentation reference gene for genetic modifications of G. mellonella. Meanwhile, it can be utilized in the development of genome editing control strategies and for gene function analyses in G. mellonella.

Matrix metalloproteinase 2 degrades collagen I to regulate ovarian development by association with an insulin-like peptide

The ovary generally undergoes tissue remodeling during larval to pupal transition, which includes membrane degeneration and ovariole growth. At the same time, the hormones produced by insects significantly change during metamorphosis. However, the regulatory mechanism for ovarian development and hormones is not fully understood in insects. Herein, we found that matrix metalloproteinase 2 (MMP2) was highly expressed in the ovarian capsules and ovarioles, and the development was abnormal after knocking out MMP2 in Bombyx mori. The process of abnormal degradation of collagen I due to MMP2 deletion, which resulted in abnormal development of ovarioles and eggs, was analyzed in detail. The proteomics of ovaries in the MMP2-knock out and wild type strains showed a critically significant difference in the expression of a protein, insulin-like peptide (ILP). Additional analysis revealed significant alteration of ILP during ovarian development, and abnormal expression of ILP significantly affected ovarian development in vivo and MMP2 expression in vitro and in vivo. These results showed that MMP2 regulation of ovarian tissue remodeling is closely related to ILP expression. Our study provides new insights into the regulatory mechanism of MMP2 and ovarian development in B. mori.

Sinuous Is a Claudin Required for Locust Molt in Locusta migratoria

The epidermal cells of insects are polarized epithelial cells that play a pivotal role in the insect's molting process. Sinuous, a pivotal structural protein involved in the formation of septate junctions among epithelial cells, is essential for its physiological function. In this study, to determine whether sinuous participates in the regulation of insect molting, we identified the sinuous gene, Lmsinu, in Locusta migratoria, which encodes a protein belonging to the claudin family and shares 62.6% identity with Drosophila's sinuous protein. Lmsinu is expressed in multiple tissues, and its expression level in the integument significantly increases prior to molting. Knockdown of Lmsinu in L. migratoria results in larval mortality during molting. Furthermore, hematoxylin and eosin and chitin staining demonstrate that the downregulation of Lmsinu led to a prolonged degradation process of the old cuticle during the molting process. Electron microscopy analysis further revealed that knockdown of Lmsinu disrupts the formation of septate junctions among epidermal cells, which are a monolayer of polarized epithelial cells, which may hinder the functionality of epidermal cells during the process of molting. In summary, these findings suggest that Lmsinu plays a role in nymph molting by regulating the formation of septate junctions among epidermal cells.

Pierisin, Cytotoxic and Apoptosis-Inducing DNA ADP-Ribosylating Protein in Cabbage Butterfly

Pierisin-1 was serendipitously discovered as a strong cytotoxic and apoptosis-inducing protein from pupae of the cabbage butterfly Pieris rapae against cancer cell lines. This 98-kDa protein consists of the N-terminal region (27 kDa) and C-terminal region (71 kDa), and analysis of their biological function revealed that pierisin-1 binds to cell surface glycosphingolipids on the C-terminal side, is taken up into the cell, and is cleaved to N- and C-terminal portions, where the N-terminal portion mono-ADP-ribosylates the guanine base of DNA in the presence of NAD to induce cellular genetic mutation and apoptosis. Unlike other ADP-ribosyltransferases, pieisin-1 was first found to exhibit DNA mono-ADP-ribosylating activity and show anti-cancer activity in vitro and in vivo against various cancer cell lines. Pierisin-1 was most abundantly produced during the transition from the final larval stage to the pupal stage of the cabbage butterfly, and this production was regulated by ecdysteroid hormones. This suggests that pierisn-1 might play a pivotal role in the process of metamorphosis. Moreover, pierisin-1 could contribute as a defense factor against parasitization and microbial infections in the cabbage butterfly. Pierisin-like proteins in butterflies were shown to be present not only among the subtribe Pierina but also among the subtribes Aporiina and Appiadina, and pierisin-2, -3, and -4 were identified in these butterflies. Furthermore, DNA ADP-ribosylating activities were found in six different edible clams. Understanding of the biological nature of pierisin-1 with DNA mono-ADP-ribosylating activity could open up exciting avenues for research and potential therapeutic applications, making it a subject of great interest in the field of molecular biology and biotechnology.

Population Density-Dependent Developmental Regulation in Migratory Locust

Insect development is intricately governed by hormonal signaling pathways, yet the pivotal upstream regulator that potentiates hormone activation remains largely elusive. The migratory locust, Locusta migratoria, exhibits population density-dependent phenotypic plasticity, encompassing traits such as flight capability, body coloration, and behavior. In this study, we elucidated a negative correlation between population density and ontogenetic development during the nymphal stage of locusts. We found that the level of density influences the developmental trajectory by modulating transcript abundance within the ecdysone signaling pathway, with knockdown of the prothoracicotropic hormone (PTTH) resulting in developmental delay. Transcriptomic analysis of locust brains across solitary and gregarious phases revealed significant differential expression of genes involved in various pathways, including protein synthesis, energy metabolism, hormonal regulation, and immunity. Notably, knockdown experiments targeting two energy regulators, adipokinetic hormone (AKH) and insulin-like polypeptide 1 (ilp1), failed to elicit changes in the developmental process in solitary locusts. However, knockdown of immunoglobulin (IG) significantly shortened the developmental time in higher-density populations. Collectively, our findings underscore the regulatory role of population density in determining developmental duration and suggest that an immune-related gene contributes to the observed differences in developmental patterns.