Insect Defense Research Articles

Parasitism by Entomopathogenic Fungi and Insect Host Defense Strategies

Entomopathogenic fungi, a group of insect pathogens, are characterized by high insecticidal efficacy and minimal environmental impact. They are commonly used as biopesticides for pest control due to their significant practical value. We here classify entomopathogenic fungi according to the process of fungal infection in hosts, changes in host behavior during infection, and mechanisms of spore transmission, and review the strategies employed by insects to resist infection, including physical barrier defenses, immune system defenses, and behavioral avoidance of fungal pathogens. This review also discusses the pathogenic mechanisms of fungi on insects and the closely linked co-evolution between fungal pathogens and insect defenses. In conclusion, a perspective on future research is provided, emphasizing the impact of insect population density and spore concentration in the environment on disease outbreaks.

Impact of Ultraviolet Radiation on Growth, Development and Antioxidant Enzymes of Tuta absoluta (Meyrick)

Ultraviolet radiation serves as a significant abiotic stressor for numerous organisms, particularly impacting insects in various ways. Tuta absoluta, a highly destructive pest infesting of the Solanaceae species, was investigated to elucidate its growth, development, and enzymatic defense mechanisms of insects in response to UV exposure. This study investigates the effects of three types of UV radiation on the lifespan, egg laying behavior, and antioxidant enzyme activities of T. absoluta. Our study revealed a significant reduction in the lifespan of T. absoluta upon exposure to both UV-A and UV-B radiation, whereas extended exposure to UV-C radiation for 120 min and 180 min resulted in a decline in its egg laying capacity. Exposure to all three types of radiation (UV-A, UV-B, and UV-C) led to an irreversible decrease in catalase (CAT) enzyme activity. Upon exposure to UV-A, there was a gradual increase in peroxidase (POD) enzyme activity; however, at 120 min post-exposure, a subsequent decrease was observed. A notable elevation in superoxide dismutase (SOD) activity was observed following exposures of both 60 min and 120 min durations under the rays of UV-A. These findings provide valuable insights into understanding the effects of UV exposure on T. absoluta as well as its potential application as a control measure, warranting further investigation.

Terrestrial insect defences in the face of metal toxicity.

Recently, there has been growing concern about the impacts of metal pollutants on insect populations, particularly as human societies increasingly rely on metal-based technologies. Unlike organic pollutants, metals - both essential and non-essential - are non-degradable and readily accumulate in insect tissues, sometimes reaching hazardous levels. While numerous studies address how insects cope with pesticide pollution, there is a notable scarcity of knowledge regarding their abilities to confront metal pollution. This paper reviews the routes of entry for metals into insect cells and the molecular damages they trigger. Additionally, it examines the defence mechanisms insects may employ to counteract metal pollution. Firstly, insects may detect and avoid metals in their environment, thereby escaping contaminated food, substrates, and oviposition sites. Secondly, the insect cuticle and gut lining, including the gut microbiota, may serve as physical barriers preventing metal entry into the hemolymph, thereby protecting other organs. Thirdly, insect cells may detoxify metals by sequestering them in metal-scavenging proteins (e.g., metallothioneins) and excreting them via faeces or the cuticle. Fourthly, when metal-related damage occurs, including oxidative stress, protein unfolding, and DNA deformation, insect cells may respond by upregulating antioxidant molecules, chaperone proteins, and DNA repair mechanisms. Enhancing our knowledge of insect-metal interactions sounds crucial for the conservation of insect populations in an increasingly metal-dependent world.

Single Disulfide Bond in Host Defense Thanatin Analog Peptides: Antimicrobial Activity, Atomic-Resolution Structures and Target Interactions.

Host defense antimicrobial peptides (AMPs) are promising lead molecules with which to develop antibiotics against drug-resistant bacterial pathogens. Thanatin, an inducible antimicrobial peptide involved in the host defense of Podisus maculiventris insects, is gaining considerable attention in the generation of novel classes of antibiotics. Thanatin or thanatin-based analog peptides are extremely potent in killing bacterial pathogens in the Enterobacteriaceae family, including drug-resistant strains of Escherichia coli and Klebsiella pneumoniae. A single disulfide bond that covalently links two anti-parallel β-strands in thanatin could be pivotal to its selective antibacterial activity and mode of action. However, potential correlations of the disulfide covalent bond with structure, activity and target binding in thanatin peptides are currently unclear to. Here, we examined a 16-residue designed thanatin peptide, namely disulfide-bonded VF16QK, and its Cys to Ser substituted variant, VF16QKSer, to delineate their structure-activity relationships. Bacterial growth inhibitory activity was only detected for the disulfide-bonded VF16QK peptide. Mechanistically, both peptides vastly differ in their bacterial cell permeabilizations, atomic-resolution structures, interactions with the LPS-outer membrane and target periplasmic protein LptAm binding. In particular, analysis of the 3-D structures of the two peptides revealed an altered folded conformation for the VF16QKSer peptide that was correlated with diminished LPS-outer membrane permeabilization and target interactions. Analysis of docked complexes of LPS-thanatin peptides indicated potential structural requirements and conformational adaptation for antimicrobial activity. Collectively, these observations contrast with those for the disulfide-bonded β-hairpin antimicrobial protegrin and tachyplesin peptides, where disulfide bonds are dispensable for activity. We surmise that the atomistic structures and associated molecular interactions presented in this work can be utilized to design novel thanatin-based antibiotics.

공작새 상징에 대한 연구

This study aims to explore the universal symbolic meanings of the peacock by examining its ecological characteristics and its depictions in myths and legends, fables, literary works, religion, and art. Based on these considerations, the study seeks to understand the symbolic meaning of the peacock in sandplay therapy cases from an analytical psychology perspective. The symbolism of peacocks was considered in six aspects: sacredness, good fortune and wealth, beauty, power (power), healing and regeneration, and immortality, and we looked at how these symbols were expressed in the process of sand play therapy. As a result of examining the symbolism of peacocks in the sand play treatment case, In the first case an adolescent client who was emotionally influenced by a mother experiencing stress and depression during pregnancy expressed their fundamental and unconscious inner sanctity. In the second case, it appeared in terms of the colorful and imposing power latent in the unconscious, and the third case in terms of the authoritative power that wanted to show off the pride of the peacock with its wings wide open. The last case was a case of a single mother woman in her 20s, who expressed the possibility of a detoxification action that allowed peacocks to heal and regenerate diseases from the harms of poisonous insects or poisonous snakes. She also demonstrated the process of realizing the state in which her elegant and noble beauty could not spread her wings and was latent in the unconscious through the peacock. Clients experienced the process of consciousness while expressing various hidden instincts through the symbolism of peacocks in sand play therapy, and for counselors, it is a significant study from the perspective of deeper understanding, empathy, and acceptance of clients.

CDK12 antagonizes a viral suppressor of RNAi to modulate antiviral RNAi in Drosophila.

The primary antiviral immunity in insects is mediated by the RNA interference (RNAi) pathway. To counteract this antiviral RNAi response, viruses employ virulence factors known as viral suppressors of RNAi (VSR). The question of whether host factors can activate a counter-counter-defense mechanism to cope with VSR-mediated RNA silencing suppression remains unanswered. In this study, cyclin-dependent kinase 12 (CDK12) was identified to interact with B2, a VSR of Flock House virus (FHV), and the critical amino acids responsible for dsRNA binding and dimerization in B2 were essential for this interaction. Silencing of CDK12 facilitated FHV RNA accumulation only in the context of B2, not for FHVΔB2. Notably, CDK12 abrogated the RNAi suppression exerted by B2. Furthermore, the knockdown of CDK12 inhibited the production of vsiRNAs in FHV-infected Drosophila cells. This study revealed that CDK12 mediated a counter-counter-defense strategy against VSR, thereby enhancing antiviral RNAi immunity in Drosophila.IMPORTANCEThe arms race between virus and host immunity is never-ending. This study enhances our understanding of antiviral defenses in insects by uncovering a novel counter-counter-defense mechanism against viral suppressors of RNA interference (VSRs). The RNA interference (RNAi) pathway serves as a primary antiviral response in insects, but viruses, such as Flock House virus (FHV), have evolved VSRs like B2 to disrupt this defense. Our research identifies cyclin-dependent kinase 12 (CDK12) as a critical host factor that interacts with the VSR B2. The discovery that CDK12 can counteract B2-mediated RNAi suppression and stimulate the production of viral small interfering RNAs (vsiRNAs) in FHV-infected Drosophila cells highlights its pivotal role in enhancing antiviral RNAi immunity. This study not only reveals a new dimension of host-virus interactions but also opens avenues for developing strategies to strengthen RNAi-based antiviral defenses.

Efficacy of botanical pesticides in insecticidal activity against the banana fruit scarring beetle Basilepta subcostata an In vitro analysis

Secondary metabolic compounds were investigated on the various insecticides from plants based on extraction and profile identified on various toxic substances. Generally, interactions between insects and plants lead to the release of various biochemical components pivotal in secondary metabolic processes and in insect defense against stimuli or insecticides. This study highlighted the efficacy of botanical pesticides containing bioactive chemicals as insecticides, operating through mechanisms such as antifeedants, repellents, protectants, and growth-disrupting hormones. Thus, secondary metabolic activity was confirmed to exhibit insecticidal properties, including the emission of signalling cues such as 2,4-Decadienal, Pterin-6-carboxylic acid, Oleic Acid, 9-Octadecenoic acid (E), and Stearic acid. Meanwhile, Principal component analysis was used to assessed the distribution of metabolites resulting from plant-insect interactions. Additionally, putative toxic substances were confirmed in repellent assays, affirming that botanical blends enhanced certain plant defenses against banana pests. Further understanding of these components and their varying efficacy levels under different conditions may be crucial in developing bio-rational control against B. subcostata under in vitro conditions. The current study aims to examine certain plant extracts as natural enemies and alternatives against the banana fruit scarring beetle B. subcostata under in vitro conditions.

The Altered Lipid Composition and Key Lipid Metabolic Enzymes in Thiacloprid-Resistant Myzus persicae, with Special Attention Paid to the Function of MpTHEM6a.

Neonicotinoid resistance is increasingly prevalent in the agricultural pest Myzus persicae. Lipids play a critical role in insect defense systems, but their contribution to insect neonicotinoid resistance is disregarded. We conducted metabolomics and transcriptomics studies on M. persicae thiacloprid-resistant (THG-R) and -susceptible (FFJ-S) populations. A total of 149 lipid metabolites were identified, with 90 upregulated and 59 downregulated in THG-R compared to in FFJ-S. Metabolites in the arachidonic acid (AA) pathway substantially varied between THG-R and FFJ-S. For example, arachidonic acid, (±)11-HETE, and prostaglandin B1 were significantly upregulated, while prostaglandin A1, tetranor-PGDM, 8,15-diHETE, and (±)11(12)-EET were significantly decreased in THG-R. Transcriptomics profiles and qPCR indicated that lipid metabolic enzymes, including fatty acid synthase (FAS), the elongase of very-long-chain fatty acids (ELO), fatty acid desaturase (FAD), and phospholipase (PL) genes, were not overexpressed in THG-R. Among the twelve thioesterase genes, only MpTHEM6a was significantly upregulated in THG-R. Knocking down the expression of MpTHEM6a in THG-R significantly increased the toxicity of the three neonicotinoids, reduced the lifespan of adults, and decreased the number of nonviable nymphs produced by female adults. The metabolites AA, (±)11-HETE, and prostaglandin B1 are potential biomarkers in neonicotinoid-resistant M. persicae. MpTHEM6a may become a potential target for combating neonicotinoid-resistant M. persicae.

RNAi-mediated silencing of transferrin promotes entomopathogens lethality in Odontotermes formosanus (Shiraki)

Transferrin (Tsf) is a highly conserved multifunctional protein involved in insect physiology, defense and development that has been developed as a novel RNA interference (RNAi)-based target for pest control. The function study of the Tsf gene in Odontotermes formosanu (Shiraki) was evaluated for synergistic control of this agroforestry pest with Serratia marcescens (SM1), Bacillus thuringiensis (Bt) or Beauveria bassiana (Bb). The Tsf gene of O. formosanus was identified and characterized. Real-time fluorescent quantitative PCR (qPCR) analysis demonstrated that OfTsf was most highly expressed in the male dealate of O. formosanus, and OfTsf was highly expressed in the hemolymph. OfTsf expression was considerably elevated after SM1, Bt or Bb infection. Furthermore, dsOfTsf treatment was effective in increasing the virulence of entomopathogens to O. formosanus. In addition, OfTsf expression was markedly upregulated in O. formosanus fed with oxidative stress inducers; reactive oxygen species (ROS) levels were significantly increased after dsOfTsf treatment. Therefore, OfTsf gene played an important role in defending against entomopathogen infection and antioxidant stress. Most importantly, our work suggested OfTsf as a potential RNAi target for the control of O. formosanus.

Gut metagenome in Insects and Its Potential in Agricultural and Industrial Applications

Metagenomics has greatly improved our understanding of microbial ecology by revealing the metagenomes of uncultured bacteria, including those associated with insects. These bacteria play important roles in insect defence, reproduction, and food absorption, which influences pest management tactics. Recent next generation sequencing advances in low-cost nucleotide and user-friendly bioinformatics have improved our ability to investigate microbial diversity in economically significant pests. Meta-omics technologies are now essential for defining microbial ecosystems, bio-surveillance, food safety, and commercial advances. Genome studies on insects and plants provide insights into pest control by discovering resistance genotypes and understanding stress-induced genomic changes. This review is focused on how herbivore specialists, such as the diamondback Plutella xylostella, adapt to host plants using gut microbiota. Metagenomic sequencing has discovered important bacteria-Enterobacter cloacae, Enterobacter asburiae, and Carnobacterium maltaromaticum- that help detoxify plant defences, breakdown cell walls, and synthesise amino acids. These findings indicate novel pest management tactics that target gut microbiota interactions. The paper continues with an overview of metagenomic DNA extraction, library creation and screening methods, especially on their applications in biotechnology and bioprocessing.

Construction of a beneficial microbes-enriched rhizosphere system assists plants in phytophagous insect defense: current status, challenges and opportunities.

The construction of a plant rhizosphere system enriched with beneficial microbes (BMs) can efficiently help plants defend against phytophagous insects. However, our comprehensive understanding of this approach is still incomplete. In this review, we methodically analyzed the progress made over the last decade, identifying both challenges and opportunities. The main methods for developing a BMs-enriched rhizosphere system include inoculating exogenous BMs into plants, amending the existing soil microbiomes with amendments, and utilizing plants to shape the soil microbiomes. BMs can assist plants in suppressing phytophagous insects across many orders, including 13 Lepidoptera, seven Homoptera, five Hemiptera, five Coleoptera, four Diptera, and one Thysanoptera species by inducing plant systemic resistance, enhancing plant tolerance, augmenting plant secondary metabolite production, and directly suppressing herbivores. Context-dependent factors such as abiotic and biotic conditions, as well as the response of insect herbivores, can affect the outcomes of BM-assisted plant defense. Several challenges and opportunities have emerged, including the development of synthetic microbial communities for herbivore control, the integration of biosensors for effectiveness assessment, the confirmation of BM targets for phytophagous insect defense, and the regulation of outcomes via smart farming with artificial intelligence. This study offers valuable insights for developing a BM-enriched rhizosphere system within an integrated pest management approach. © 2024 Society of Chemical Industry.

Octanoic acid kills Lucilia sericata (Diptera: Calliphoridae) by affecting two major defence systems: cuticular free fatty acids and immunocompetent cells

This work examines the insecticidal activity of octanoic acid (C8:0), a short-chain fatty acid detected in entomopathogenic fungus – Conidiobolus coronatus medium, against Lucilia sericata larvae and adults. The LD50 value was calculated as 3.04±0.26 µg/mg (3040 mg/kg) of insect body mass, which places the compound in category 5 of acute toxicity (slightly hazardous). The presented research also describes its probable mechanism, with a particular focus on changes in two main insect defense mechanisms: (1) the composition of the cuticle (GC–MS analysis) and (2) immunocompetent cells (microscopic analysis of cultured hemocytes). More precisely, octanoic acid application resulted in changes in cuticular free fatty acid (FFA) profiles in both adults and larvae; generally, treatment increased short-chain FFAs, and a decrease of middle- and long-chain FFAs. Both in vivo and in vitro applications of octanoic acid resulted in vacuolisation, disintegration, and destruction of nets formed by plasmatocytes. As the compound has also previously been found to be toxic against Galleria mellonella, it appears to have lethal potential against insects in both the Orders Diptera and Lepidoptera, indicating it may have strong entomopathogenic potential. It is worth noting that octanoic acid is approved as a food additive with well-documented insecticidal activity, and hence may be a valuable component in the design of new insecticides that are safe for both humans and the environment.

Genome-Wide Transcriptomic and Metabolomic Analyses Unveiling the Defence Mechanisms of Populus tremula against Sucking and Chewing Insect Herbivores.

Plants and insects coevolved as an evolutionarily successful and enduring association. The molecular arms race led to evolutionary novelties regarding unique mechanisms of defence and detoxification in plants and insects. While insects adopt mechanisms to conquer host defence, trees develop well-orchestrated and species-specific defence strategies against insect herbivory. However, current knowledge on the molecular underpinnings of fine-tuned tree defence responses against different herbivore insects is still restricted. In the current study, using a multi-omics approach, we unveiled the defence response of Populus tremula against aphids (Chaitophorus populialbae) and spongy moths (Lymantria dispar) herbivory. Comparative differential gene expression (DGE) analyses revealed that around 272 and 1203 transcripts were differentially regulated in P. tremula after moth and aphid herbivory compared to uninfested controls. Interestingly, 5716 transcripts were differentially regulated in P. tremula between aphids and moth infestation. Further investigation showed that defence-related stress hormones and their lipid precursors, transcription factors, and signalling molecules were over-expressed, whereas the growth-related counterparts were suppressed in P. tremula after aphid and moth herbivory. Metabolomics analysis documented that around 37% of all significantly abundant metabolites were associated with biochemical pathways related to tree growth and defence. However, the metabolic profiles of aphid and moth-fed trees were quite distinct, indicating species-specific response optimization. After identifying the suitable reference genes in P. tremula, the omics data were further validated using RT-qPCR. Nevertheless, our findings documented species-specific fine-tuning of the defence response of P. tremula, showing conservation on resource allocation for defence overgrowth under aphid and moth herbivory. Such findings can be exploited to enhance our current understanding of molecular orchestration of tree responses against herbivory and aid in developing insect pest resistance P. tremula varieties.

Natural occurrence, infection dynamics, and molecular characterization of nucleopolyhedrovirus (SpfrNPV) infecting fall armyworm, Spodoptera frugiperda (J. E. Smith) from maize ecosystems in Gujarat, India

This comprehensive study investigates the stage-wise infection dynamics of Nucleopolyhedrovirus (NPV) in fall armyworm, Spodoptera frugiperda (J. E. Smith) larvae across distinct stages of maize crop in Panchmahal and Mahisagar districts of Gujarat, India during the kharif season in 2021. The examination of month-wise mean data reveals a pronounced pattern of NPV prevalence, with the highest infection observed during the cob formation stage (28.74 %), followed by flowering and tasseling (20.23 %), and the vegetative stage (13.93 %). Block specific analyses highlight variations in infection rates, with notable differences between districts and stages. Correlation coefficient analysis indicates a significant and positive relationship between specific crop stages and NPV infection. Regression equations are established, demonstrating a positive increase in natural NPV infection during different crop stages. Weather parameter analysis reveals significant correlations between temperature, humidity, sunshine hours, and NPV infection. The phylogenetic analysis of NPV polyhedrin sequences indicates species-specific clustering within S. frugiperda and a broader genus-specific association. Motif pattern analysis identifies conserved motifs in NPV polyhedrins. Protein structure predictions and Molecular docking studies predicted interactions between polyhedrin and chitinase, suggesting a potential role in the insect's defense against NPV. The bioassay results indicated increased susceptibility of early larvae to NPV, emphasizing the potential for optimizing biocontrol strategies. Overall, this study contributes valuable insights into the ecological and molecular aspects of NPV infection dynamics, offering a significance understanding for developing effective pest management strategies and also underscores its significance in promoting sustainable agriculture.

ROLE OF MADANPHALA IN MANAGEMENT OF MUSHIKA VISHA - A REVIEW ARTICLE

An ingredient that is used in various formulations in the treatment of Vishas (poisons). Many formulations for the management of various poisons like snake bite, keetavisha (insect poisons), etc. have been explained in Ayurveda treatise that contains it as an ingredient.in the present article we are discussing regarding the Madanphala and ghrita of Tanduliyaka in management of Mushika visha. Madanphala is having properties of Laghu, Ruksha Guna, Kashaya, Katu, Tikta Rasa and Ushna Veerya. It acts as a Vranashodhan and Ropan properties. Paste of Madanphala applied over skin and wounds helps in Vranashodhan therefore used in the Mushika visha effectively. Tanduliya (Amaranthus spinosus) prepared in the form of Ghrita (Ghee) is said to reduce the bastivedana (pain in urinary system) and anaha (Distension of abdomen due to obstruction to passage of urine and stools) in the complications caused because of visha

Insights into midgut cell types and their crucial role in antiviral immunity in the lepidopteran model Bombyx mori.

The midgut, a vital component of the digestive system in arthropods, serves as an interface between ingested food and the insect's physiology, playing a pivotal role in nutrient absorption and immune defense mechanisms. Distinct cell types, including columnar, enteroendocrine, goblet and regenerative cells, comprise the midgut in insects and contribute to its robust immune response. Enterocytes/columnar cells, the primary absorptive cells, facilitate the immune response through enzyme secretions, while regenerative cells play a crucial role in maintaining midgut integrity by continuously replenishing damaged cells and maintaining the continuity of the immune defense. The peritrophic membrane is vital to the insect's innate immunity, shielding the midgut from pathogens and abrasive food particles. Midgut juice, a mixture of digestive enzymes and antimicrobial factors, further contributes to the insect's immune defense, helping the insect to combat invading pathogens and regulate the midgut microbial community. The cutting-edge single-cell transcriptomics also unveiled previously unrecognized subpopulations within the insect midgut cells and elucidated the striking similarities between the gastrointestinal tracts of insects and higher mammals. Understanding the intricate interplay between midgut cell types provides valuable insights into insect immunity. This review provides a solid foundation for unraveling the complex roles of the midgut, not only in digestion but also in immunity. Moreover, this review will discuss the novel immune strategies led by the midgut employed by insects to combat invading pathogens, ultimately contributing to the broader understanding of insect physiology and defense mechanisms.

A life-and-death struggle: interaction of insects with entomopathogenic fungi across various infection stages.

Insects constitute approximately 75% of the world's recognized fauna, with the majority of species considered as pests. Entomopathogenic fungi (EPF) are parasitic microorganisms capable of efficiently infecting insects, rendering them potent biopesticides. In response to infections, insects have evolved diverse defense mechanisms, prompting EPF to develop a variety of strategies to overcome or circumvent host defenses. While the interaction mechanisms between EPF and insects is well established, recent findings underscore that their interplay is more intricate than previously thought, especially evident across different stages of EPF infection. This review primarily focuses on the interplay between EPF and the insect defense strategies, centered around three infection stages: (1) Early infection stage: involving the pre-contact detection and avoidance behavior of EPF in insects, along with the induction of behavioral responses upon contact with the host cuticle; (2) Penetration and intra-hemolymph growth stage: involving the initiation of intricate cellular and humoral immune functions in insects, while symbiotic microbes can further contribute to host resistance; (3) Host insect's death stage: involving the ultimate confrontation between pathogens and insects. Infected insects strive to separate themselves from the healthy population, while pathogens rely on the infected insects to spread to new hosts. Also, we discuss a novel pest management strategy underlying the cooperation between EPF infection and disturbing the insect immune system. By enhancing our understanding of the intricate interplay between EPF and the insect, this review provides novel perspectives for EPF-mediated pest management and developing effective fungal insecticides.

Recent trends in insect gut immunity.

The gut is a crucial organ in insect defense against various pathogens and harmful substances in their environment and diet. Distinct insect gut compartments possess unique functionalities contributing to their physiological processes, including immunity. The insect gut's cellular composition is vital for cellular and humoral immunity. The peritrophic membrane, mucus layer, lumen, microvilli, and various gut cells provide essential support for activating and regulating immune defense mechanisms. These components also secrete molecules and enzymes that are imperative in physiological activities. Additionally, the gut microbiota initiates various signaling pathways and produces vitamins and minerals that help maintain gut homeostasis. Distinct immune signaling pathways are activated within the gut when insects ingest pathogens or hazardous materials. The pathway induced depends on the infection or pathogen type; include immune deficiency (imd), Toll, JAK/STAT, Duox-ROS, and JNK/FOXO regulatory pathways. These pathways produce different antimicrobial peptides (AMPs) and maintain gut homeostasis. Furthermore, various signaling mechanisms within gut cells regulate insect gut recovery following infection. Although some questions regarding insect gut immunity in different species require additional study, this review provides insights into the insect gut's structure and composition, commensal microorganism roles in Drosophila melanogaster and Tenebrio molitor life cycles, different signaling pathways involved in gut immune systems, and the insect gut post-infection recovery through various signaling mechanisms.

Different myrosinases activate sequestered glucosinolates in larvae and adults of the horseradish flea beetle

β-Glucosidases play an important role in the chemical defense of many insects by hydrolyzing and thereby activating glucosylated pro-toxins that are either synthesized de novo or sequestered from the insect's diet. The horseradish flea beetle, Phyllotreta armoraciae, sequesters pro-toxic glucosinolates from its brassicaceous host plants and possesses endogenous β-thioglucosidase enzymes, known as myrosinases, for glucosinolate activation. Here, we identify three myrosinase genes in P. armoraciae (PaMyr) with distinct expression patterns during beetle ontogeny. By using RNA interference, we demonstrate that PaMyr1 is responsible for myrosinase activity in adults, whereas PaMyr2 is responsible for myrosinase activity in larvae. Compared to PaMyr1 and PaMyr2, PaMyr3 was only weakly expressed in our laboratory population, but may contribute to myrosinase activity in larvae. Silencing of PaMyr2 resulted in lower larval survival in a predation experiment and also reduced the breakdown of sequestered glucosinolates in uninjured larvae. This suggests that PaMyr2 is involved in both activated defense and the endogenous turnover of sequestered glucosinolates in P. armoraciae larvae. In activity assays with recombinant enzymes, PaMyr1 and PaMyr2 preferred different glucosinolates as substrates, which was consistent with the enzyme activities in crude protein extracts from adults and larvae, respectively. These differences were unexpected because larvae and adults sequester the same glucosinolates. Possible reasons for different myrosinase activities in Phyllotreta larvae and adults are discussed.

Identification and immune analysis of antimicrobial peptides from the cigarette beetle (Lasioderma serricorne).

Antimicrobial peptides (AMPs) in insects are endogenous peptides that are effector components of the innate defense system of the insect. AMPs may serve as antimicrobial agents because of their small molecular weight and broad-spectrum antimicrobial activity. In this study, we performed transcriptome analysis of cigarette beetle (Lasioderma serricorne) larvae, parasitized by the ectoparasitic wasp, Anisopteromalus calandrae. Several AMP genes were significantly upregulated following A.calandrae parasitism, postulating the hypothesis that the parasitization enhanced the host's resistance against pathogenic microorganisms through the regulation of host AMP genes. Specifically, 3 AMP genes (LsDef1, LsDef2, and LsCole) were significantly upregulated and we studied their immune function in L.serricorne. Immune challenge and functional analysis showed that LsCole was responsible for the immune response against Gram-negative and Gram-positive bacteria, while LsDef1 and LsDef2 were involved in insect defense against Gram-positive bacteria. Purified recombinant LsCole exhibited antimicrobial activities against the Gram-negative bacterium Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. LsDef2 showed an antibacterial effect against S.aureus. LsCole and LsDef2 exhibited antibiofilm activity against S.aureus. The 2 AMPs disrupted cell membranes and caused leakage of S.aureus cell contents. The results indicated that the 3 AMPs in L.serricorne are involved in the innate immunity of this pest insect. These AMPs may have potential as antimicrobial agents for bacterial infection chemotherapy. Hence, data are discussed in relation to new control strategies with greater biosafety against pest insects with use of microbial biocontrol agents in combination with RNA interference against the insect's defensive AMP genes.