Molecular Mechanisms of Wing Polymorphism in Insects

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.

Body color plasticity of Diaphorina citri reflects a response to environmental stress

Body color polyphenism is common in Diaphorina citri. Previous studies compared physiological characteristics in D. citri, but the ecological and biological significance of its body color polyphenism remains poorly understood. We studied the ecological and molecular effects of stressors related to body color in D. citri. Crowding or low temperature induced a high proportion of gray morphs, which had smaller bodies, lower body weight, and greater susceptibility to the insecticide dinotefuran. We performed transcriptomic and metabolomics analysiis of 2 color morphs in D. citri. Gene expression dynamics revealed that the differentially expressed genes were predominantly involved in energy metabolism, including fatty acid metabolism, amino acid metabolism, and carbohydrate metabolism. Among these genes, plexin, glycosidase, phospholipase, take out, trypsin, and triacylglycerol lipase were differentially expressed in 2 color morphs, and 6 hsps (3 hsp70, hsp83, hsp90, hsp68) were upregulated in gray morphs. The metabolome data showed that blue morphs exhibited a higher abundance of fatty acid and amino acid, whereas the content of carbohydrates was elevated in gray morphs. This study partly explains the body color polyphenism of D. citri and provides insights into the molecular changes of stress response of D. citri.

Genetic Variants Underlying Plasticity in Natural Populations of Spadefoot Toads: Environmental Assessment versus Phenotypic Response

Many organisms facultatively produce different phenotypes depending on their environment, yet relatively little is known about the genetic bases of such plasticity in natural populations. In this study, we describe the genetic variation underlying an extreme form of plasticity--resource polyphenism--in Mexican spadefoot toad tadpoles, Spea multiplicata. Depending on their environment, these tadpoles develop into one of two drastically different forms: a carnivore morph or an omnivore morph. We collected both morphs from two ponds that differed in which morph had an adaptive advantage and performed genome-wide association studies of phenotype (carnivore vs. omnivore) and adaptive plasticity (adaptive vs. maladaptive environmental assessment). We identified four quantitative trait loci associated with phenotype and nine with adaptive plasticity, two of which exhibited signatures of minor allele dominance and two of which (one phenotype locus and one adaptive plasticity locus) did not occur as minor allele homozygotes. Investigations into the genetics of plastic traits in natural populations promise to provide novel insights into how such complex, adaptive traits arise and evolve.

Dual-role regulator of a novel miR-3040 in photoperiod-mediated wing dimorphism and wing development in green peach aphid

Wing dimorphism is regarded as an important phenotypic plasticity involved in the migration and reproduction of aphids. However, the signal transduction and regulatory mechanism of wing dimorphism in aphids are still unclear. Herein, the optimal environmental conditions were first explored for inducing winged offspring of green peach aphid, and the short photoperiod was the most important environmental cue to regulate wing dimorphism. Compared to 16 L:8 D photoperiod, the proportion of winged offspring increased to 90% under 8 L:16 D photoperiod. Subsequently, 5 differentially expressed microRNAs (miRNAs) in aphids treated with long and short photoperiods were identified using small RNA sequencing, and a novel miR-3040 was identified as a vital miRNA involved in photoperiod-mediated wing dimorphism. More specifically, the inhibition of miR-3040 expression could reduce the proportion of winged offspring induced by short photoperiod, whereas its activation increased the proportion of winged offspring under long photoperiod. Meanwhile, the expression level of miR-3040 in winged aphids was about 2.5 times that of wingless aphids, and the activation or inhibition of miR-3040 expression could cause wing deformity, revealing the dual-role regulator of miR-3040 in wing dimorphism and wing development. In summary, the current study identified the key environmental cue for wing dimorphism in green peach aphid, and the first to demonstrate the dual-role regulator of miR-3040 in photoperiod-mediated wing dimorphism and wing development.

The AAA-ATPase Ter94 regulates wing size in Drosophila by suppressing the Hippo pathway

Insect wing development is a fascinating and intricate process that involves the regulation of wing size through cell proliferation and apoptosis. In this study, we find that Ter94, an AAA-ATPase, is essential for proper wing size dependently on its ATPase activity. Loss of Ter94 enables the suppression of Hippo target genes. When Ter94 is depleted, it results in reduced wing size and increased apoptosis, which can be rescued by inhibiting the Hippo pathway. Biochemical experiments reveal that Ter94 reciprocally binds to Mer, a critical upstream component of the Hippo pathway, and disrupts its interaction with Ex and Kib. This disruption prevents the formation of the Ex-Mer-Kib complex, ultimately leading to the inactivation of the Hippo pathway and promoting proper wing development. Finally, we show that hVCP, the human homolog of Ter94, is able to substitute for Ter94 in modulating Drosophila wing size, underscoring their functional conservation. In conclusion, Ter94 plays a positive role in regulating wing size by interfering with the Ex-Mer-Kib complex, which results in the suppression of the Hippo pathway.

Crucial roles of specialized chitinases in elytral and hindwing cuticles construction in Leptinotarsa decemlineata

BACKGROUND

The Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a major potato (Solanum tuberosum) pest, infesting over 16 million km2 and causing substantial economic losses. The insect cuticle forms an apical extracellular matrix (ECM) envelope covering exposed organs to direct morphogenesis and confer structural protection. While select chitinase (Cht) genes have proven essential for larval development, their potential activities directing ECM remodeling underlying adult wing maturation remain undefined.

RESULTS

We investigated the expression patterns and performed an oral RNA interference (RNAi) screen targeting 19 LdChts in late-instar L. decemlineata larvae. Subsequently, we assessed their effects on adult eclosion and wing characteristics. Knockdown of LdCht5, LdCht7, LdCht10, LdIDGF2, and LdIDGF4, as well as others from Group IV (LdCht15, LdCht12, LdCht17, and LdCht13) and Groups VII-X (LdCht2, LdCht11, LdCht1, and LdCht3), resulting in shrunken, misshapen elytra with reduced areal density, as well as transverse wrinkling and impaired wing-tip folding in hindwings. Scanning electron micrographs revealed eroded elytral ridges alongside thinned, ruptured hindwing veins, indicative of mechanical fragility post-LdCht suppression. Spectroscopic analysis uncovered biomolecular alterations underlying the elytral anomalies, including decreases in peaks representing chitin, proteins, and lipids. This loss of essential ECM components provides evidence for the fragility, wrinkling, and shrinkage observed in the RNAi groups.

CONCLUSION

Our findings elucidate the crucial role of chitinases in the turnover of chitinous cuticles on beetle wings, offering insights into RNAi-based control strategies against this invasive pest. © 2024 Society of Chemical Industry.

Wing Plasticity Is Associated with Growth and Energy Metabolism in Two Color Morphs of the Pea Aphid

The pea aphid, Acyrthosiphon pisum, is a major pest of legume crops, exhibiting distinct polymorphism in terms of wings and body color. We found that, under crowded conditions, the red morph A. pisum produced more winged offspring than the green morph. The signaling pathways involved in aphid wing determination, like insulin and ecdysone, also play important roles in regulating growth, development, and metabolism. Thus, here, we examined the association between the wing-producing ability and the growth rate, development time, reproductive capacity, and energy metabolism in these two color morphs. The growth rate of red morphs was significantly higher than that of green morphs, whereas green morphs produced more offspring during the first 6 days of the adult stage. Red morphs accumulated higher levels of glycogen and triglycerides and consumed more triglycerides during starvation; however, green aphids consumed more trehalose during food deprivation. Red aphids exhibited stronger starvation tolerance, possibly due to their higher triglyceride catabolic activity. Furthermore, the expression levels of genes involved in the insulin pathway, glycolysis, and lipolysis in red aphids were higher than those in green aphids. These results suggest that the wing-producing ability of the pea aphid may be associated with its growth and metabolism, which may be due to the shared regulatory signaling pathways.

Wing expansion functional analysis of ion transport peptide gene in Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

Ion transport peptide (ITP), a superfamily of arthropod neuropeptides, serves a crucial role in regulating various physiological processes such as diuresis, ecdysis behavior, and wing expansion. However, the molecular characteristics, expression profile, and role of ITP in Sogatella furcifera are poorly understood. To elucidate the characteristics and biological function of ITP in S. furcifera, we employed reverse transcription-polymerase chain reaction (RT-PCR) and RNA interference (RNAi) methods. The identified SfITP gene encodes 117 amino acids. The expression of SfITP gradually increased followed the formation of 3-day-old of 5th instar nymph, peaking initially at 40 min after eclosion, and reaching another peak 24 h after eclosion, with particularly high expression levels in thorax and wing tissues. Notably, SfITP RNAi in 3rd instar nymphs of S. furcifera significantly inhibited the transcript levels of SfITP, resulting in 55% mortality and 78% wing deformity. These findings suggests that SfITP is involved in the regulation of wing expansion in S. furcifera, providing insights into the regulation of insect wing expansion and contributing to the molecular understanding of this process.

Aphid gene expression following polerovirus acquisition is host species dependent

Upon acquisition of persistent circulative viruses such as poleroviruses, the virus particles transcytose through membrane barriers of aphids at the midgut and salivary glands via hemolymph. Such intricate interactions can influence aphid behavior and fitness and induce associated gene expression in viruliferous aphids. Differential gene expression can be evaluated by omics approaches such as transcriptomics. Previously conducted aphid transcriptome studies used only one host species as the source of virus inoculum. Viruses typically have alternate hosts. Hence, it is not clear how alternate hosts infected with the same virus isolate alter gene expression in viruliferous vectors. To address the question, this study conducted a transcriptome analysis of viruliferous aphids that acquired the virus from different host species. A polerovirus, cotton leafroll dwarf virus (CLRDV), which induced gene expression in the cotton aphid, Aphis gossypii Glover, was assessed using four alternate hosts, viz., cotton, hibiscus, okra, and prickly sida. Among a total of 2,942 differentially expressed genes (DEGs), 750, 310, 1,193, and 689 genes were identified in A. gossypii that acquired CLRDV from infected cotton, hibiscus, okra, and prickly sida, respectively, compared with non-viruliferous aphids that developed on non-infected hosts. A higher proportion of aphid genes were overexpressed than underexpressed following CLRDV acquisition from cotton, hibiscus, and prickly sida. In contrast, more aphid genes were underexpressed than overexpressed following CLRDV acquisition from okra plants. Only four common DEGs (heat shock protein, juvenile hormone acid O-methyltransferase, and two unannotated genes) were identified among viruliferous aphids from four alternate hosts. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations indicated that the acquisition of CLRDV induced DEGs in aphids associated with virus infection, signal transduction, immune systems, and fitness. However, these induced changes were not consistent across four alternate hosts. These data indicate that alternate hosts could differentially influence gene expression in aphids and presumably aphid behavior and fitness despite being infected with the same virus isolate.

Comparative analysis of the diversity of symbionts in fat body of long- and short-winged brown planthoppers

The microbial community structure plays an important role in the internal environment of brown planthopper (BPH), Nilaparvata lugens (Hemiptera: Delphacidae), which is an indispensable part to reflect the internal environment of BPH. Wing dimorphism is a strategy for balancing flight and reproduction of insects. Here, quantitative fluorescence PCR was used to analyse the number and changes of the symbionts in the fat body of long- and short-winged BPHs at different developmental stages. A metagenomic library was constructed based on the 16 S rRNA sequence and internal transcribed spacer sequence for high-throughput sequencing, to analyze the community structure and population number of the symbionts of long- and short-winged BPHs, and to make functional prediction. This study enriches the connotation of BPH symbionts, and laid a theoretical foundation for the subsequent study of BPH-symbionts interaction and the function of symbionts in the host.

Characterization of two Bursicon genes and their association with wing development in the brown citrus aphid, Aphis citricidus

The tanning hormone, Bursicon, is a neuropeptide secreted by the insect nervous system that functions as a heterodimer composed of Burs-α and Burs-β subunits. It plays a critical role in the processes of cuticle tanning and wing expansion in insects. In this study, we successfully identified the AcBurs-α and AcBurs-β genes in Aphis citricidus. The open reading frames of AcBurs-α and AcBurs-β were 480 and 417 bp in length, respectively. Both AcBurs-α and AcBurs-β exhibited 11 conserved cysteine residues. AcBurs-α and AcBurs-β were expressed during all developmental stages of A. citricidus and showed high expression levels in the winged aphids. To investigate the potential role of AcBurs-α and AcBurs-β in wing development, we employed RNA interference (RNAi) techniques. With the efficient silencing of AcBurs-α (44.90%) and AcBurs-β (52.31%), malformed wings were induced in aphids. The proportions of malformed wings were 22.50%, 25.84%, and 38.34% in dsAcBurs-α-, dsAcBur-β-, and dsAcBurs-α + dsAcBur-β-treated groups, respectively. Moreover, feeding protein kinase A inhibitors (H-89) also increased the proportion of malformed wings to 30.00%. Feeding both double-stranded RNA and inhibitors (H-89) significantly downregulated the wing development-related genes nubbin, vestigial, notch and spalt major. Silence of vestigial through RNAi also led to malformed wings. Meanwhile, the exogenous application of 3 hormones that influence wing development did not affect the expression level of AcBursicon genes. These findings indicate that AcBursicon genes plays a crucial role in wing development in A. citricidus; therefore, it represents a potential molecular target for the control of this pest through RNAi-based approaches.

Evolution and molecular mechanisms of wing plasticity in aphids

Aphids present a fascinating example of phenotypic plasticity, in which a single genotype can produce dramatically different winged and wingless phenotypes that are specialized for dispersal versus reproduction, respectively. Recent work has examined many aspects of this plasticity, including its evolution, molecular control mechanisms, and genetic variation underlying the trait. In particular, exciting discoveries have been made about the signaling pathways that are responsible for controlling the production of winged versus wingless morphs, including ecdysone, dopamine, and insulin signaling, and about how specific genes such as REPTOR2 and vestigial are regulated to control winglessness. Future work will likely focus on the role of epigenetic mechanisms, as well as developing transgenic tools for more thoroughly dissecting the role of candidate plasticity-related genes.

Rapid sexual signal diversification is facilitated by permissive females

The initial process by which novel sexual signals evolve remains unclear, because rare new variants are susceptible to loss by drift or counterselection imposed by prevailing female preferences.1,2,3,4 We describe the diversification of an acoustic male courtship signal in Hawaiian populations of the field cricket Teleogryllus oceanicus, which was brought about by the evolution of a brachypterous wing morph ("small-wing") only 6 years ago.5 Small-wing has a genetic basis and causes silence or reduced-amplitude signaling by miniaturizing male forewings, conferring protection against an eavesdropping parasitoid, Ormia ochracea.5 We found that wing reduction notably increases the fundamental frequency of courtship song from an average of 5.1 kHz to 6.4 kHz. It also de-canalizes male song, broadening the range of peak signal frequencies well outside normal song character space. As courtship song prompts female mounting and is sexually selected,6,7,8,9 we evaluated two scenarios to test the fate of these new signal values. Females might show reduced acceptance of small-wing males, imposing counterselection via prevailing preferences. Alternatively, females might accept small-wing males as readily as long-wing males if their window of preference is sufficiently wide. Our results support the latter. Females preferred males who produced some signal over none, but they mounted sound-producing small-wing males as often as sound-producing long-wing males. Indiscriminate mating can facilitate the persistence of rare, novel signal values. If female permissiveness is a general characteristic of the earliest stages of sexual signal evolution, then taxa with low female mate acceptance thresholds should be more prone to diversification via sexual selection.

A plant virus manipulates the long-winged morph of insect vectors

Wing dimorphism of insect vectors is a determining factor for viral long-distance dispersal and large-area epidemics. Although plant viruses affect the wing plasticity of insect vectors, the potential underlying molecular mechanisms have seldom been investigated. Here, we found that a planthopper-vectored rice virus, rice stripe virus (RSV), specifically induces a long-winged morph in male insects. The analysis of field populations demonstrated that the long-winged ratios of male insects are closely associated with RSV infection regardless of viral titers. A planthopper-specific and testis-highly expressed gene, Encounter, was fortuitously found to play a key role in the RSV-induced long-winged morph. Encounter resembles malate dehydrogenase in the sequence, but it does not have corresponding enzymatic activity. Encounter is upregulated to affect male wing dimorphism at early larval stages. Encounter is closely connected with the insulin/insulin-like growth factor signaling pathway as a downstream factor of Akt, of which the transcriptional level is activated in response to RSV infection, resulting in the elevated expression of Encounter. In addition, an RSV-derived small interfering RNA directly targets Encounter to enhance its expression. Our study reveals an unreported mechanism underlying the direct regulation by a plant virus of wing dimorphism in its insect vectors, providing the potential way for interrupting viral dispersal.

Functional analysis of Ornithine decarboxylase in manipulating the wing dimorphism in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

The brown planthopper (BPH, Nilaparvata lugens), a major insect pest of rice, can make a shift in wing dimorphism to adapt to complex external environments. Our previous study showed that NlODC (Ornithine decarboxylase in N. lugens) was involved in wing dimorphism of the brown planthopper. Here, further experiments were conducted to reveal possible molecular mechanism of NlODC in manipulating the wing dimorphism. We found that the long-winged rate (LWR) of BPH was significantly reduced after RNAi of NlODC or injection of DFMO (D, L-α-Difluoromethylornithine), and LWR of males and females significantly decreased by 21.7% and 34.6%, respectively. Meanwhile, we also examined the contents of three polyamines under DFMO treatment and found that the contents of putrescine and spermidine were significantly lower compared to the control. After 3rd instar nymphs were injected with putrescine and spermidine, LWR was increased significantly in both cases, and putrescine was a little bit more effective, with 5.6% increase in males and 11.4% in females. Three days after injection of dsNlODC, injection of putrescine and spermidine rescued LWR to the normal levels. In the regulation of wing differentiation in BPH, NlODC mutually antagonistic to NlAkt may act through other signaling pathways rather than the classical insulin signaling pathway. This study illuminated a physiological function of an ODC gene involved in wing differentiation in insects, which could be a potential target for pest control.

Sexually dimorphic morphology, feeding behavior and gene expression profiles in cotton aphid Aphis gossypii

BACKGROUND

Sexual dimorphism exists in most insects; however, less is known about sexual dimorphism in aphids. In this study, we identified sexually dimorphic differences in morphology, feeding behavior and gene expression between sexual females and males of the cotton aphid through electron microscopy, electrical penetration graph techniques and RNA sequencing.

RESULTS

All males were alate with a slender reddish-yellow body and abdominal yellow-black stripes, whereas all sexual females were apterous with a pudgy green body. Sensillum types on the antennae were identical between the two sexes, although males had more sensilla, possibly because the antennae are significantly longer in males compared with sexual females. In terms of feeding behavior, males spent more time probing mesophyll cells and the phloem sieve, and salivating into the phloem sieve. By contrast, sexual females spent more time ingesting xylem sap. In total, 510 and 724 genes were specifically expressed in sexual females and males, respectively, and were significantly enriched in signaling pathways related to reproduction for sexual females (e.g. ovarian steroidogenesis, oxytocin signaling pathway) and energy and flight for males (e.g. thermogenesis, insulin signaling pathway). Moreover, 8551 differentially expressed genes were identified between the two sexes, of which the 3720 upregulated genes in sexual females were mostly enriched in signaling pathways of metabolism and energy, such as thermogenesis and the citrate cycle.

CONCLUSION

This study provides insight into sexual dimorphism in aphids and lays a foundation for revealing the molecular mechanism underlying differences between the two sexes in cotton aphid. © 2023 Society of Chemical Industry.

Why do viruses make aphids winged?

Aphids are hosts to diverse viruses and are important vectors of plant pathogens. The spread of viruses is heavily influenced by aphid movement and behaviour. Consequently, wing plasticity (where individuals can be winged or wingless depending on environmental conditions) is an important factor in the spread of aphid-associated viruses. We review several fascinating systems where aphid-vectored plant viruses interact with aphid wing plasticity, both indirectly by manipulating plant physiology and directly through molecular interactions with plasticity pathways. We also cover recent examples where aphid-specific viruses and endogenous viral elements within aphid genomes influence wing formation. We discuss why unrelated viruses with different transmission modes have convergently evolved to manipulate wing formation in aphids and whether this is advantageous for both host and virus. We argue that interactions with viruses are likely shaping the evolution of wing plasticity within and across aphid species, and we discuss the potential importance of these findings for aphid biocontrol.

Chromosome-level genome assembly and population genomic analysis provide novel insights into the immunity and evolution of Sogatella furcifera

Sogatella furcifera is a destructive agricultural pest causing large threats to rice production in China and Southeast Asian countries. Despite recent breakthroughs in long-read sequencing, high quality genomic data are very limited in S. furcifera. In present study, a chromosome-level assembly of the S. furcifera genome was completed (0.64 GB), comprising 15 chromosomes covered 95.04% of the estimated genome size, along with other 624 small scaffolds making up the remaining 4.96% of the genome of S. furcifera. A total of 24,669 protein-coding genes, 1211 long noncoding RNA and 7595 circular RNA transcripts were predicted in this study. Comparative genomic analysis revealed rapidly evolved genes were associated with multiple immune-related pathways in S. furcifera. Genome resequencing of 44 individuals from 12 geographic populations revealed frequent gene flow among populations. The systemic genomic analysis will provide more insights into the understanding of the immunity and evolutionary adaptation of S. furcifera.

Insight into phenotypic plasticity in planthoppers

Planthoppers possess an impressive ability to exhibit phenotypic plasticity, which allows them to adjust their morphology for migration, overwintering, and adaptation to different environmental conditions. The wing and color polyphenism are the two most outward morphologies. Wing polyphenism serves as a classic illustration of a life history trade-off between reproduction and migration, while color polyphenism is potentially correlated with the insect development and immunity. In this review, we present the important contributions that link environment cues to wing and color polyphenism, and highlight recent advances in insulin/insulin-like growth factor signaling-forkhead transcription factor subgroup O (FoxO) pathway-mediated wing development and tyrosine-melanin pathway-mediated coloration. Further work, particularly in the identification of the genes that FoxO regulates and in the elucidation of the intracellular signals that link the stimuli to the tyrosine-melanin pathway, is required.

The Wnt pathway regulates wing morph determination in Acyrthosiphon pisum

Wing dimorphism occurs in insects as a survival strategy to adapt to environmental changes. In response to environmental cues, mother aphids transmit signals to their offspring, and the offspring either emerge as winged adults or develop as wingless adults with degeneration of the wing primordia in the early instar stage. However, how the wing morph is determined in the early instar stage is still unclear. Here, we established a surgical sampling method to obtain precise wing primordium tissues for transcriptome analysis. We identified Wnt as a regulator of wing determination in the early second instar stage in the pea aphid. Inhibiting Wnt signaling via knockdown of Wnt2, Wnt11b, the Wnt receptor-encoding gene fz2 or the downstream targets vg and omb resulted in a decreased proportion of winged aphids. Activation of Wnt signaling via knockdown of miR-8, an inhibitor of the Wnt/Wg pathway, led to an increased proportion of winged aphids. Furthermore, the wing primordia of wingless nymphs underwent apoptosis in the early second instar, and cell death was activated by knockdown of fz2 under the wing-inducing condition. These results indicate that the developmental plasticity of aphid wings is modulated by the intrinsic Wnt pathway in response to environmental challenges.

Comparison of the signaling pathways of wing dimorphism regulated by biotic and abiotic stress in the brown planthopper

Wing polymorphism is an evolutionary trait that is widely present in various insects and provides a model system for studying the evolutionary significance of insect dispersal. The brown planthopper (BPH, Nilaparvata lugens) can alter its wing morphs under biotic and abiotic stress. However, whether differential signaling pathways are induced by the 2 types of stress remain largely unknown. Here, we screened a number of candidate genes through weighted gene co-expression network analysis (WGCNA) and found that ornithine decarboxylase (NlODC), a key enzyme in the synthesis of polyamines, was associated with wing differentiation in BPH and mainly responded to abiotic stress stimuli. We analyzed the Kyoto Encyclopedia of Genes and Genomes enrichment pathways of differentially expressed genes under the 2 stresses by transcriptomic comparison, and found that biotic stress mainly influenced insulin-related signaling pathways while abiotic stress mainly influenced hormone-related pathways. Moreover, we found that insulin receptor 1 (NlInR1) may regulate wing differentiation of BPH by responding to both biotic and abiotic stress, but NlInR2 only responded to biotic stress. Similarly, the juvenile hormone epoxide hydrolase associated with juvenile hormone degradation and NlODC may regulate wing differentiation mainly through abiotic stress. A model based on the genes and stresses to modulate the wing dimorphism of BPH was proposed. These findings present a comprehensive molecular mechanism for wing polymorphism in BPH induced by biotic and abiotic stress.

FoxO and rotund form a binding complex governing wing polyphenism in planthoppers

Wing polyphenism is found in a variety of insects and offers an attractive model system for studying the evolutionary significance of dispersal. The Forkhead box O (FoxO) transcription factor (TF) acts as a wing-morph switch that directs wing buds developing into long-winged (LW) or short-winged morphs in wing-dimorphic planthoppers, yet the regulatory mechanism of the FoxO module remains elusive. Here, we identified the zinc finger TF rotund as a potential wing-morph regulator via transcriptomic analysis and phenotypic screening in the brown plathopper, Nilaparvata lugens. RNA interference-mediated knockdown of rotund antagonized the LW development derived from in the context of FoxO depletion or the activation of the insulin/insulin-like growth factor signaling cascade, reversing long wings into intermediate wings. In vitro binding assays indicated that rotund physically binds to FoxO to form the FoxO combinatorial code. These findings broaden our understanding of the complexity of transcriptional regulation governing wing polyphenism in insects.

Functional evaluation of the insulin/insulin-like growth factor signaling pathway in determination of wing polyphenism in pea aphid

Wing polyphenism is a common phenomenon that plays key roles in environmental adaptation of insects. Insulin/insulin-like growth factor signaling (IIS) pathway is a highly conserved pathway in regulation of metabolism, development, and growth in metazoans. It has been reported that IIS is required for switching of wing morph in brown planthopper via regulating the development of the wing pad. However, it remains elusive whether and how IIS pathway regulates transgenerational wing dimorphism in aphid. In this study, we found that pairing and solitary treatments can induce pea aphids to produce high and low percentage winged offspring, respectively. The expression level of ILP5 (insulin-like peptide 5) in maternal head was significantly higher upon solitary treatment in comparison with pairing, while silencing of ILP5 caused no obvious change in the winged offspring ratio. RNA interference-mediated knockdown of FoxO (Forkhead transcription factor subgroup O) in stage 20 embryos significantly increased the winged offspring ratio. The results of pharmacological and quantitative polymerase chain reaction experiments showed that the embryonic insulin receptors may not be involved in wing polyphenism. Additionally, ILP4 and ILP11 exhibited higher expression levels in 1st wingless offspring than in winged offspring. We demonstrate that FoxO negatively regulates the wing morph development in embryos. ILPs may regulate aphid wing polyphenism in a developmental stage-specific manner. However, the regulation may be not mediated by the canonical IIS pathway. The findings advance our understanding of IIS pathway in insect transgenerational wing polyphenism.

Salivary carbonic anhydrase II in winged aphid morph facilitates plant infection by viruses

Aphids are the most common insect vector transmitting hundreds of plant viruses. Aphid wing dimorphism (winged vs. wingless) not only showcases the phenotypic plasticity but also impacts virus transmission; however, the superiority of winged aphids in virus transmission over the wingless morph is not well understood. Here, we show that plant viruses were efficiently transmitted and highly infectious when associated with the winged morph of Myzus persicae and that a salivary protein contributed to this difference. The carbonic anhydrase II (CA-II) gene was identified by RNA-seq of salivary glands to have higher expression in the winged morph. Aphids secreted CA-II into the apoplastic region of plant cells, leading to elevated accumulation of H+. Apoplastic acidification further increased the activities of polygalacturonases, the cell wall homogalacturonan (HG)-modifying enzymes, promoting degradation of demethylesterified HGs. In response to apoplastic acidification, plants accelerated vesicle trafficking to enhance pectin transport and strengthen the cell wall, which also facilitated virus translocation from the endomembrane system to the apoplast. Secretion of a higher quantity of salivary CA-II by winged aphids promoted intercellular vesicle transport in the plant. The higher vesicle trafficking induced by winged aphids enhanced dispersal of virus particles from infected cells to neighboring cells, thus resulting in higher virus infection in plants relative to the wingless morph. These findings imply that the difference in the expression of salivary CA-II between winged and wingless morphs is correlated with the vector role of aphids during the posttransmission infection process, which influences the outcome of plant endurance of virus infection.

Functional characterization of five developmental signaling network genes in the white-backed planthopper: Potential application for pest management

BACKGROUND

The white-backed planthopper (WBPH, Sogatella furcifera) is a major rice pest that exhibits condition dependent wing dimorphisms - a macropterous (long wing) form and a brachypterous (short wing) form. Although, the gene cascade that regulates wing development and dimorphic differentiation has been largely defined, the utility of these genes as targets for pest control has yet to be fully explored.

RESULTS

Five genes typically associated with the developmental signaling network, armadillo (arm), apterous A (apA), scalloped (sd), dachs (d), and yorkie (yki) were identified from the WBPH genome and their roles in wing development assessed following RNA interference (RNAi)-mediated knockdown. At 5 days-post injection, transcript levels for all five targets were substantially decreased compared with the dsGFP control group. Among the treatment groups, those injected with dsSfarm had the most pronounced effects on transcript reduction, mortality (95 ± 3%), and incidence (45 ± 3%) of wing deformities, whereas those injected with dsSfyki had the lowest incidence (6.7 ± 4%). To assess the utility of topical RNAi for Sfarm, we used a spray-based approach that complexed a large-scale, bacteria-based double-stranded RNA (dsRNA) expression pipeline with star polycation (SPc) nanoparticles. Rice seedlings infested with third and fourth instar nymphs were sprayed with SPc-dsRNA formulations and RNAi phenotypic effects were assessed over time. At 2 days post-spray, Sfarm transcript levels decreased by 86 ± 9.5% compared with dsGFP groups, and the subsequent incidences of mortality and wing defects were elevated in the treatment group.

CONCLUSIONS

This study characterized five genes in the WBPH developmental signaling cascade, assessed their impact on survival and wing development via RNAi, and developed a nanoparticle-dsRNA spray approach for potential field control of WBPH. © 2023 Society of Chemical Industry.

Biological Characteristics and Energy Metabolism of Migrating Insects

Through long-distance migration, insects not only find suitable breeding locations and increase the survival space and opportunities for the population but also facilitate large-scale material, energy, and information flow between regions, which is important in maintaining the stability of agricultural ecosystems and wider natural ecosystems. In this study, we summarize the changes in biological characteristics such as morphology, ovarian development, reproduction, and flight capability during the seasonal migration of the insect. In consideration of global research work, the interaction between flight and reproduction, the influence and regulation of the insulin-like and juvenile hormone on the flight and reproductive activities of migrating insects, and the types of energy substances, metabolic processes, and hormone regulation processes during insect flight are elaborated. This systematic review of the latest advances in the studies on insect migration biology and energy metabolism will help readers to better understand the biological behavior and regulation mechanism of the energy metabolism of insect migration.

One genome, multiple phenotypes: decoding the evolution and mechanisms of environmentally induced developmental plasticity in insects

Plasticity in developmental processes gives rise to remarkable environmentally induced phenotypes. Some of the most striking and well-studied examples of developmental plasticity are seen in insects. For example, beetle horn size responds to nutritional state, butterfly eyespots are enlarged in response to temperature and humidity, and environmental cues also give rise to the queen and worker castes of eusocial insects. These phenotypes arise from essentially identical genomes in response to an environmental cue during development. Developmental plasticity is taxonomically widespread, affects individual fitness, and may act as a rapid-response mechanism allowing individuals to adapt to changing environments. Despite the importance and prevalence of developmental plasticity, there remains scant mechanistic understanding of how it works or evolves. In this review, we use key examples to discuss what is known about developmental plasticity in insects and identify fundamental gaps in the current knowledge. We highlight the importance of working towards a fully integrated understanding of developmental plasticity in a diverse range of species. Furthermore, we advocate for the use of comparative studies in an evo-devo framework to address how developmental plasticity works and how it evolves.

Orco mutagenesis causes deficiencies in olfactory sensitivity and fertility in the migratory brown planthopper, Nilaparvata lugens

BACKGROUND

The migratory brown planthopper (BPH), Nilaparvata lugens (Hemiptera: Delphacidae), is the most destructive pest affecting rice plants in Asia and feeds exclusively on rice. Studies have investigated the olfactory response of BPHs to the major rice volatile compounds in rice. The insect olfactory co-receptor (Orco) is a crucial component of the olfactory system and is essential for odorant detection. Functional analysis of the Orco gene in BPHs would aid in the identification of their host preference.

RESULTS

We identified the BPH Orco homologue (NlOrco) by Blast searching the BPH transcriptome with the Drosophila Orco gene sequence. Spatiotemporal analysis indicated that NlOrco is first expressed in the later egg stage, and is expressed mainly in the antennae in adult females. A NlOrco-knockout line (NlOrco-/- ) was generated through clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated mutagenesis. The NlOrco-/- mutants showed no response to rice volatile compounds and consequently no host-plant preference. In addition, NlOrco-/- mutants exhibited extended nymphal duration and impaired fecundity compared with wild-type BPHs.

CONCLUSION

Our findings indicated that BPHs exhibit strong olfactory responses to major rice volatile compounds and suggest that NlOrco is required for the maximal fitness of BPHs. Our results may facilitate the identification of potential target genes or chemical compounds for BPH control applications. © 2022 Society of Chemical Industry.

Sexual size and shape dimorphism, and allometric scaling in the pupal and adult traits of Eristalis tenax

The patterns and amount of variation in size, shape, and/or life history traits between females and males are fundamentally important to gain the comprehensive understanding of the evolution of phenotypic diversity. In addition, the covariation of phenotypic traits can significantly contribute to morphological diversification and sexual dimorphism (SD). Using linear and geometric morphometrics, 237 Eristalis tenax specimens sampled from five populations were, therefore, comparatively assessed for the variation in sexual size dimorphism (SSD), sexual shape dimorphism (SShD), and life history traits, as well as for trait covariation (ontogenetic and static allometry). Pupal body, adult wing, and body mass traits were analyzed. Female-biased SSD was observed for pupal length, width, and centroid size, adult wing centroid size, mass, wing loading, and wing area. Conversely, pupal length/width ratio, developmental time, and mass were not found to be sexually dimorphic. Next, wing SShD, but not pupal body SShD was revealed, while allometry was found to be an important "determinant of SD" at the adult stage, with only a minor impact at the pupal stage. By comparing the patterns of covariance (based on allometric slope and intercept) between respective body mass and morphometric traits of pupae and adults, greater variation in allometric slopes was found in adult traits, while static allometries of the two stages significantly differed, as well. Finally, the results indicate that changes in the allometric intercept could be an important source of intraspecific variation and SD in drone fly adults.

Screening and identification of genes associated with flight muscle histolysis of the house cricket Acheta domesticus

Introduction: Flight muscle histolysis, as an important survival strategy, is a widespread phenomenon in insects and facilitates adaptation to the external environment in various insect taxa. However, the regulatory mechanism underlying this phenomenon in Orthoptera remains unknown. Methods: In this study, the flight muscle histolysis in the house cricket Acheta domesticus was investigated by transcriptomics and RNA interference. Results: The results showed that flight muscle histolysis in A. domesticus was standard and peaked within 9 days after eclosion of adult crickets, and there was no significant difference in the peak time or morphology of flight muscle histolysis between males and females. In addition, the differentially expressed genes between before and after flight muscle histolysis were studied, of which AdomFABP, AdomTroponin T and AdomActin were identified as candidate genes, and after injecting the dsRNA of these three candidates, only the downregulated expression of AdomFABP led to flight muscle histolysis in A. domesticus. Furthermore, the expression level of AdomFABP was compared between before and after flight muscle histolysis based on RT-qPCR. Disscussion: We speculated that AdomFABP might play a role in the degradation of flight muscle by inhibiting muscle development. Our findings laid a molecular foundation for understanding the flight muscle histolysis.

The oriental armyworm genome yields insights into the long-distance migration of noctuid moths

The oriental armyworm, Mythimna separata, is known for its long-distance seasonal migration and environment-dependent phase polymorphisms. Here, we present a chromosome-level genome reference and integrate multi-omics, functional genetics, and behavioral assays to explore the genetic bases of the hallmark traits of M. separata migration. Gene family comparisons show expansion of gustatory receptor genes in this cereal crop pest. Functional investigation of magnetoreception-related genes and associated flight behaviors suggest that M. separata may use the geomagnetic field to guide orientation in its nocturnal flight. Comparative transcriptome characterizes a suite of genes that may confer the observed plasticity between phases, including genes involved in protein processing, hormone regulation, and dopamine metabolism. We further report molecular signatures that underlie the dynamic regulation of a migratory syndrome coordinating reproduction and flight. Our study yields insights into environment-dependent developmental plasticity in moths and advances our understanding of long-distance migration in nocturnal insect pests.

Functional genomic tools for emerging model species

Most studies in the field of ecology and evolution aiming to connect genotype to phenotype rarely validate identified loci using functional tools. Recent developments in RNA interference (RNAi) and clustered regularly interspaced palindromic repeats (CRISPR)-Cas genome editing have dramatically increased the feasibility of functional validation. However, these methods come with specific challenges when applied to emerging model organisms, including limited spatial control of gene silencing, low knock-in efficiencies, and low throughput of functional validation. Moreover, many functional studies to date do not recapitulate ecologically relevant variation, and this limits their scope for deeper insights into evolutionary processes. We therefore argue that increased use of gene editing by allelic replacement through homology-directed repair (HDR) would greatly benefit the field of ecology and evolution.

Delta and jagged are candidate target genes of RNAi biopesticides for the control of Nilaparvata lugens

The brown planthopper (BPH; Nilaparvata lugens) is an important pest in rice cultivation, and chemical pesticide over-use and ineffectiveness of existing Bt transgenic rice against piercing-sucking insects make novel control methods necessary. RNA interference (RNAi) biopesticide is a new type of product with high efficiency and specificity and are simple to use. The Notch signaling pathway has extensive and important physiological functions and plays a key role in the development of insects. In this study, two key ligand genes of the Notch signaling pathway, delta (dl) and jagged (jag), were selected and their lethal effects and functional analysis were systematically evaluated using a stable short-winged population (Brachypterous strain) and a long-winged population (Macropterous strain) of BPHs. The full-length coding sequences of Nldl and Nljag comprised 1,863 and 3,837 base pairs, encoding 620 and 1,278 amino acids, respectively. The nucleic acid sequences of Nldl and Nljag were identical between the two strains. The expression levels of Nldl and Nljag were relatively high in the head of the nymphs, followed by those in the abdomen. Through RNAi treatment, we found that injection of BPH nymphs of both strains with dsNldl (10-50 ng/nymph) or dsNljag (100 ng/nymph) produced lethal or teratogenic effects. dsRNA treatment showed excellent inhibitory effects on the expression of target genes on days 1 and 5, suggesting that RNAi rapidly exhibits effects which persist for long periods of time in BPHs. Taken together, our results confirm the potential of Nldl and Nljag as target genes of RNAi biopesticides, and we propose optimized dosages for the control of BPHs.

Mitochondria dysfunction impairs Tribolium castaneum wing development during metamorphosis

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.

The transcription factor Zfh1 acts as a wing-morph switch in planthoppers

Insect wing polyphenism is characterized by its ability to produce two or more distinct wing morphs from a single genotype in response to changing environments. However, the molecular basis of this phenomenon remains poorly understood. Here, we identified a zinc finger homeodomain transcription factor Zfh1 that acts as an upstream regulator for the development of long-winged (LW) or shorted-winged (SW) morphs in planthoppers. Knockdown of Zfh1 directs SW-destined nymphs to develop into LW morphs by down-regulating the transcriptional level of FoxO, a prominent downstream effector of the insulin/IGF signaling (IIS) pathway. The balance between transcriptional regulation via the Zfh1-FoxO cascade and post-translational regulation via the IIS-FoxO cascade provides a flexible regulatory mechanism for the development of alternative wing morphs. These findings help us understand how phenotypic diversity is generated by altering the activity of conserved proteins, and provide an extended framework for the evolution of wing morphological diversity in insects.

Nutrition-dependent juvenile hormone sensitivity promotes flight-muscle degeneration during the aphid dispersal-reproduction transition

In insects, the loss of flight typically involves a dispersal-reproduction transition, but the underlying molecular mechanisms remain poorly understood. In the parthenogenetic pea aphid Acyrthosiphon pisum, winged females undergo flight-muscle degeneration after flight and feeding on new host plants. Similarly, topical application of a juvenile hormone (JH) mimic to starved aphids also induces flight-muscle degeneration. We found that feeding preferentially upregulated the expression of the JH receptor gene Met and a JH-inducible gene, Kr-h1, in the flight muscles, and, thus, enhanced tissue-specific JH sensitivity and signaling. RNAi-mediated knockdown of Kr-h1 prevented flight-muscle degeneration. Likewise, blocking nutritional signals by pharmacological inhibition of the target of rapamycin complex 1 (TORC1) impaired JH sensitivity of the flight muscles in feeding aphids and subsequently delayed muscle degeneration. RNA-sequencing analysis revealed that enhanced JH signaling inhibited the transcription of genes involved in the tricarboxylic acid cycle, likely resulting in reduction of the energy supply, mitochondrial dysfunction and muscle-fiber breakdown. This study shows that nutrient-dependent hormone sensitivity regulates developmental plasticity in a tissue-specific manner, emphasizing a relatively underappreciated mechanism of hormone sensitivity in modulating hormone signaling.

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

The insulin receptor (IR) is a transmembrane protein that is activated by ligands in insulin signaling pathways. The IR has been considered as a novel therapeutic target for clinical intervention, considering the overexpression of its protein and A-isoform in multiple cancers, Alzheimer’s disease, and Type 2 diabetes mellitus in humans. Meanwhile, it may also serve as a potential target in pest management due to its multiple physiological influences in insects. In this review, we provide an overview of the structural and molecular biology of the IR, functions of IRs in humans and insects, physiological and nonpeptide small molecule modulators of the IR, and the regulating mechanisms of the IR. Xenobiotic compounds and the corresponding insecticidal chemicals functioning on the IR are also discussed. This review is expected to provide useful information for a better understanding of human IR-related diseases, as well as to facilitate the development of novel small-molecule activators and inhibitors of the IR for use as medicines or pesticides.

Knockdown of the chromatin remodeling ATPase gene Brahma impairs the reproductive potential of the brown planthopper, Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive pests in rice-growing regions of Asia. Extensive studies have suggested that SWI/SNF chromatin remodeling ATPase Brahma (BRM) plays multiple roles in the insect model Drosophila. Yet much less is known about the physiological properties for NlBRM. In the present study, the cloned full-length cDNA of NlBRM was 5637 bp and contained an ORF of 5292 bp encoding a 194.53 kD protein. The spatiotemporal dynamics of NlBRM was investigated by qPCR, which showed that it was abundantly expressed in the egg and ovary. Then significant downregulation of NlBRM by dsRNA injection had a relatively greater impact on female survival than male. Moreover, the number of oviposition marks of the NlBRM-RNAi females were declined by 61.11% - 73.33% compared with the controls during the subsequent 5 days after dsRNA injection. Meanwhile, the number of newly hatched BPH nymphs also decreased correspondingly by 93.56% - 100%. Phenotypic analysis revealed that none of normally banana-shaped eggs were discernable in the ovaries of NlBRM-deficient females, where mRNA expression of N. lugens vitellogenin gene was also reduced. Our results demonstrated that NlBRM played a crucial role in ovarian development and fecundity of BPH, likely by regulating the vitellogenin gene in vivo, which could be as a promising target for parental RNAi-based control of this serious rice pest.

Neuroendocrinal and molecular basis of flight performance in locusts

Insect flight is a complex physiological process that involves sensory and neuroendocrinal control, efficient energy metabolism, rhythmic muscle contraction, and coordinated wing movement. As a classical study model for insect flight, locusts have attracted much attention from physiologists, behaviorists, and neuroendocrinologists over the past decades. In earlier research, scientists made extensive efforts to explore the hormone regulation of metabolism related to locust flight; however, this work was hindered by the absence of molecular and genetic tools. Recently, the rapid development of molecular and genetic tools as well as multi-omics has greatly advanced our understanding of the metabolic, molecular, and neuroendocrinal basis of long-term flight in locusts. Novel neural and molecular factors modulating locust flight and their regulatory mechanisms have been explored. Moreover, the molecular mechanisms underlying phase-dependent differences in locust flight have also been revealed. Here, we provide a systematic review of locust flight physiology, with emphasis on recent advances in the neuroendocrinal, genetic, and molecular basis. Future research directions and potential challenges are also addressed.

Pea aphid winged and wingless males exhibit reproductive, gene expression, and lipid metabolism differences

Alternative, intraspecific phenotypes offer an opportunity to identify the mechanistic basis of differences associated with distinctive life history strategies. Wing dimorphic insects, in which both flight-capable and flight-incapable individuals occur in the same population, are particularly well-studied in terms of why and how the morphs trade off flight for reproduction. Yet despite a wealth of studies examining the differences between female morphs, little is known about male differences, which could arise from different causes than those acting on females. Here we examined reproductive, gene expression, and biochemical differences between pea aphid (Acyrthosiphon pisum) winged and wingless males. We find that winged males are competitively superior in one-on-one mating circumstances, but wingless males reach reproductive maturity faster and have larger testes. We suggest that males tradeoff increased local matings with concurrent possible inbreeding for outbreeding and increased ability to find mates. At the mechanistic level, differential gene expression between the morphs revealed a possible role for activin and insulin signaling in morph differences; it also highlighted genes not previously identified as being functionally important in wing polymorphism, such as genes likely involved in sperm production. Further, we find that winged males have higher lipid levels, consistent with their use as flight fuel, but we find no consistent patterns of different levels of activity among five enzymes associated with lipid biosynthesis. Overall, our analyses provide evidence that winged versus wingless males exhibit differences at the reproductive, gene expression, and biochemical levels, expanding the field's understanding of the functional aspects of morph differences.

miR-92a-1-p5 Modulated Expression of the flightin Gene Regulates Flight Muscle Formation and Wing Extension in the Pea Aphid, Acyrthosiphon pisum (Hemiptera: Aphidoidea)

Aphids exhibit wing polyphenism. Winged and wingless aphid morphs are produced by parthenogenesis depending on population density and host plant quality. Recent studies showed that microRNAs in alate and apterous individuals have differential expression and are involved in wing dimorphism of Acyrthosiphon pisum. From which miR-92a-1-p5 can target the mRNA of flight muscle gene flightin in vitro, but what effect they have on wing development of aphid is unclear. Here with the nanocarrier-delivered RNA interference (RNAi) method, flightin gene was knocked down in winged nymphs of A. pisum. Results showed that the majority (63.33%) of adults had malformed wings, the shape of dorsal longitudinal muscle (DLM) was deformed severely, the dorsoventral flight muscle (DVM) became wider and looser in aphids with flightin reduction compared with the negative control. Overexpression of miR-92a-1-p5 caused decreased expression of flightin and malformed wings of aphids, with a mutant ratio of 62.50%. Morphological analysis of flight musculature showed the consistent result as that with flightin knockdown. These results suggest that flightin is essential for flight musculature formation and wing extension in A. pisum, which can be modulated by miR-92a-1-p5.

Photoperiod controls wing polyphenism in a water strider independently of insulin receptor signalling

Insect wing polyphenism has evolved as an adaptation to changing environments and a growing body of research suggests that the nutrient-sensing insulin receptor signalling pathway is a hot spot for the evolution of polyphenisms, as it provides a direct link between growth and available nutrients in the environment. However, little is known about the potential role of insulin receptor signalling in polyphenisms which are controlled by seasonal variation in photoperiod. Here, we demonstrate that wing length polyphenism in the water strider Gerris buenoi is determined by photoperiod and nymphal density, but is not directly affected by nutrient availability. Exposure to a long-day photoperiod is highly inducive of the short-winged morph whereas high nymphal densities moderately promote the development of long wings. Using RNA interference we demonstrate that, unlike in several other species where wing polyphenism is controlled by nutrition, there is no detectable role of insulin receptor signalling in wing morph induction. Our results indicate that the multitude of possible cues that trigger wing polyphenism can be mediated through different genetic pathways and that there are multiple genetic origins to wing polyphenism in insects.

Review: Trait plasticity during plant-insect interactions: From molecular mechanisms to impact on community dynamics

Phenotypic plasticity, prevalent in all domains of life, enables organisms to cope with unpredictable or novel changes in their growing environment. Plants represent an interesting example of phenotypic plasticity which also directly represents and affects the dynamics of biological interactions occurring in a community. Insects, which interact with plants, manifest phenotypic plasticity in their developmental, physiological, morphological or behavioral traits in response to the various host plant defenses induced upon herbivory. However, plant-insect interactions are generally more complex and multidimensional because of their dynamic association with their respective microbiomes and macrobiomes. Moreover, these associations can alter plant and insect responses towards each other by modulating the degree of phenotypic plasticity in their various traits and studying them will provide insights into how plants and insects reciprocally affect each other's evolutionary trajectory. Further, we explore the consequences of phenotypic plasticity on relationships and interactions between plants and insects and its impact on their development, evolution, speciation and ecological organization. This overview, obtained after exploring and comparing data obtained from several inter-disciplinary studies, reveals how genetic and molecular mechanisms, underlying plasticity in traits, impact species interactions at the community level and also identifies mechanisms that could be exploited in breeding programs.

Rice Defense against Brown Planthopper Partially by Suppressing the Expression of Transferrin Family Genes of Brown Planthopper

Transferrins are multifunctional proteins, but their role in the interaction of rice and brown planthopper (BPH) remains unclear. In this study, the full-length cDNA of transferrin genes NlTsf1, NlTsf2, and NlTsf3 was cloned. Reverse transcription quantitative polymerase chain reaction showed that the expressions of NlTsf1 and NlTsf3 were significantly suppressed in BPH reared on the resistant rice R1 by 68.0 and 86.7%, respectively, compared with that on the susceptible S9. The survival rate decreased to 3.3% for dsNlTsf3-treated nymphs, to 58.9% for dsNlTsf1, and to 56.7% for dsNlTsf2 on day 11. RNAi of NlTsf3 against females largely reduced the number of eggs by 99.4%, and it decreased by 48.6% for dsNlTsf1 but did not significantly decrease for dsNlTsf2. Collectively, NlTsf1, NlTsf2, and NlTsf3 are essential for the survival and fecundity of BPH and are differentially involved in the interaction between rice and BPH. Therefore, NlTsf1 and NlTsf3 may be used as targets to control BPH.

Defense in Social Insects: Diversity, Division of Labor, and Evolution

All social insects defend their colony from predators, parasites, and pathogens. In Oster and Wilson's classic work, they posed one of the key paradoxes about defense in social insects: Given the universal necessity of defense, why then is there so much diversity in mechanisms? Ecological factors undoubtedly are important: Predation and usurpation have imposed strong selection on eusocial insects, and active defense by colonies is a ubiquitous feature of all social insects. The description of diverse insect groups with castes of sterile workers whose main duty is defense has broadened the purview of social evolution in insects, in particular with respect to caste and behavior. Defense is one of the central axes along which we can begin to organize and understand sociality in insects. With the establishment of social insect models such as the honey bee, new discoveries are emerging regarding the endocrine, neural, and gene regulatory mechanisms underlying defense in social insects. The mechanisms underlying morphological and behavioral defense traits may be shared across diverse groups, providing opportunities for identifying both conserved and novel mechanisms at work. Emerging themes highlight the context dependency of and interaction between factors that regulate defense in social insects.

Locust density shapes energy metabolism and oxidative stress resulting in divergence of flight traits

Migratory locusts display striking phenotypical plasticity. Gregarious locusts at high density can migrate long distances and cause huge economic losses of crops. By contrast, solitary locusts at low density have limited ability in long-distance flight. However, the mechanisms underlying such flight capacity variation are poorly understood. Here, we found that the flight muscle of solitary locusts has a higher catabolic capacity that is associated with greater reactive oxygen species (ROS) generation during high-velocity flights. By contrast, a relatively lower catabolic capacity in gregarious locusts is associated with lower ROS generation during long-distance flights. This finding uncovers the metabolic mechanism of locust flight trait alteration in response to density changes and enhances our understanding of the biological processes enabling locust migration.

Flight ability is essential for the enormous diversity and evolutionary success of insects. The migratory locusts exhibit flight capacity plasticity in gregarious and solitary individuals closely linked with different density experiences. However, the differential mechanisms underlying flight traits of locusts are largely unexplored. Here, we investigated the variation of flight capacity by using behavioral, physiological, and multiomics approaches. Behavioral assays showed that solitary locusts possess high initial flight speeds and short-term flight, whereas gregarious locusts can fly for a longer distance at a relatively lower speed. Metabolome–transcriptome analysis revealed that solitary locusts have more active flight muscle energy metabolism than gregarious locusts, whereas gregarious locusts show less evidence of reactive oxygen species production during flight. The repression of metabolic activity by RNA interference markedly reduced the initial flight speed of solitary locusts. Elevating the oxidative stress by paraquat injection remarkably inhibited the long-distance flight of gregarious locusts. In respective crowding and isolation treatments, energy metabolic profiles and flight traits of solitary and gregarious locusts were reversed, indicating that the differentiation of flight capacity depended on density and can be reshaped rapidly. The density-dependent flight traits of locusts were attributed to the plasticity of energy metabolism and degree of oxidative stress production but not energy storage. The findings provided insights into the mechanism underlying the trade-off between velocity and sustainability in animal locomotion and movement.

Genome-wide analysis of long non-coding RNAs and their association with wing development in Aphis citricidus (Hemiptera: Aphididae)

Long non-coding RNAs (lncRNAs) play critical roles in the various physiological processes of insects. The wing is a successful adaptation allowing insects to escape from unfavorable environments, while information on lncRNAs related to wing development is limited. In this study, we constructed 12 libraries from two RNA-seq comparisons: 4th instar winged nymphs versus winged adults and 4th instar wingless nymphs versus wingless adults in the brown citrus aphid Aphis citricidus, to identify the wing development-associated lncRNAs. A total of 2914 lncRNAs were identified and 50 lncRNAs were differentially expressed during the 4th instar winged nymphs to winged adults transition, and 28 lncRNAs changed during the 4th instar wingless nymphs to wingless adults transition. The differentially expressed lncRNAs were grouped into six clusters according to the expression patterns in the combined two-winged morphs. lncRNA Ac_lnc54106.1 was up-regulated during 4th instar winged nymphs to winged adults transition, but a lack of change during the 4th instar wingless nymphs to wingless adults transition implied a critical role in the specific regulation of wing development. RNA interference of Ac_lnc54106.1 resulted in malformed wings. Targets prediction, expression patterns, and RNAi assay results showed that Ac_lnc54106.1 may target the PiggyBac transposable element-derived protein 4 (PGBD4) gene, decrease expression of the canonical wing development-related genes, and finally regulate wing development. The systematic identification of lncRNAs in an aphid increases our understanding of how non-coding RNA mediates the wing plasticity of insects.

Animal Migration: An Overview of One of Nature's Great Spectacles

The twenty-first century has witnessed an explosion in research on animal migration, in large part due to a technological revolution in tracking and remote-sensing technologies, along with advances in genomics and integrative biology. We now have access to unprecedented amounts of data on when, where, and how animals migrate across various continents and oceans. Among the important advancements, recent studies have uncovered a surprising level of variation in migratory trajectories at the species and population levels with implications for both speciation and the conservation of migratory populations. At the organismal level, studies linking molecular and physiological mechanisms to traits that support migration have revealed a remarkable amount of seasonal flexibility in many migratory animals. Advancements in the theory for why animals migrate have resulted in promising new directions for empirical studies. We provide an overview of the current state of knowledge and promising future avenues of study.

Differential DNA methylation between long-winged and short-winged adults of Nilaparvata lugens

Nilaparvata lugens, a catastrophic rice pest in South East Asia, has adults with wing dimorphism. DNA methylation has been proved to play an important role in regulation of phenotype differentiation in insects. In this study, methylation sensitive amplification polymorphism (MSAP) was used to investigate the cytosine methylation state at CCGG sites in macropterous male adults (MMA) and brachypterous male adults (BMA) of brown planthopper. In MMA, the fully methylated ratio was 2.96%, hemi-methylated ratio 3.83% and total methylated ratio 6.79%. In BMA, they were 5.53%, 4.19% and 9.72%, respectively. There were significant differences in the methylation of the target sites (CCGG) between MMA and BMA (ØST = 0.2614, P = 0.0354). Based the PCoA results, a much clear separation were also shown between MMA and BMA along the first coordinate (38.8% of variance explained). We also cloned and got nine satisfactory sequences with different methylation states between MMA and BMA. Two of them have similarity with male-specific sequence in chromosome Y and lipophorin receptor gene in N. lugens, respectively. The result showed that the methylation patterns and levels were different between two wing phenotypes of N. lugens, and will facilitate research on the epigenetic mechanism of insect wing dimorphism.

Neofunctionalization of a second insulin receptor gene in the wing-dimorphic planthopper, Nilaparvata lugens

A single insulin receptor (InR) gene has been identified and extensively studied in model species ranging from nematodes to mice. However, most insects possess additional copies of InR, yet the functional significance, if any, of alternate InRs is unknown. Here, we used the wing-dimorphic brown planthopper (BPH) as a model system to query the role of a second InR copy in insects. NlInR2 resembled the BPH InR homologue (NlInR1) in terms of nymph development and reproduction, but revealed distinct regulatory roles in fuel metabolism, lifespan, and starvation tolerance. Unlike a lethal phenotype derived from NlInR1 null, homozygous NlInR2 null mutants were viable and accelerated DNA replication and cell proliferation in wing cells, thus redirecting short-winged–destined BPHs to develop into long-winged morphs. Additionally, the proper expression of NlInR2 was needed to maintain symmetric vein patterning in wings. Our findings provide the first direct evidence for the regulatory complexity of the two InR paralogues in insects, implying the functionally independent evolution of multiple InRs in invertebrates.

The highly conserved insulin/insulin-like growth factor signaling pathway plays a pivotal role in growth, development, and various physiological processes across a wide phylogeny of organisms. Unlike a single InR in the model species such as the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans, most insect lineages have two or even three InR copies. However, the function of the alternative InRs remains elusive. Here, we created a homozygous mutation for a second insulin receptor (InR2) in the wing-dimorphic brown planthopper (BPH), Nilaparvata lugens, using the clustered regularly interspaced palindromic repeats/CRISPR-associated (CRISPR/Cas9) system. Our findings revealed that InR2 possesses functions distinct from the BPH InR homologue (NlInR1), indicating that multiple InR paralogues may have evolved independently and may have functionally diversified in ways more complex than previously expected in invertebrates.