Insect Immune System Research Articles

NO Synthesis in Immune-Challenged Locust Hemocytes and Potential Signaling to the CNS.

Simple SummaryInsects, in the same way as vertebrates, are exposed to a broad variety of pathogens but lack their adaptive immune system. Relying on their innate immune system, they respond to pathogens by phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. In this study, we evaluated the production of the cytotoxic gaseous radical nitric oxide (NO) in hemocytes, the immune cells of the model insect Locusta migratoria in response to various immune stimuli. Both sessile and circulating hemocytes responded to gram-negative Escherichia coli and gram-positive Streptococcus suis injection with a strong increase in NO production. In contrast, the gram-positive bacterium Staphylococcus aureus elicited only a minor response. In addition, bacteria were encapsulated by hemocytes. Since NO is an important neurotransmitter, NO-producing hemocytes were tested on the locust central nervous system (CNS) in an embryo culture model. CNS neurons responded with a distinct increase in production of the second messenger, cGMP. This is indicative of the influence of the immune response on the CNS. Our findings show that NO production in hemocytes and capsule formation need complex stimuli and contribute to the understanding of neuroimmune interactions in insects.Similar to vertebrates, insects are exposed to a broad variety of pathogens. The innate insect immune system provides several response mechanisms such as phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. The cytotoxic nitric oxide (NO), which is also a neurotransmitter, is involved in the response to bacterial infections in various insects but has rarely been shown to be actually produced in hemocytes. We quantified the NO production in hemocytes of Locusta migratoria challenged with diverse immune stimuli by immunolabeling the by-product of NO synthesis, citrulline. Whereas in untreated adult locusts less than 5% of circulating hemocytes were citrulline-positive, the proportion rose to over 40% after 24 hours post injection of heat-inactivated bacteria. Hemocytes surrounded and melanized bacteria in locust nymphs by forming capsules. Such sessile hemocytes also produced NO. As in other insect species, activated hemocytes were found dorsally, close to the heart. In addition, we frequently observed citrulline-positive hemocytes and capsules near the ventral nerve cord. Neurites in the CNS of sterile locust embryos responded with elevation of the second messenger cGMP after contact with purified adult NO-producing hemocytes as revealed by immunofluorescence. We suggest that hemocytes can mediate a response in the CNS of an infected animal via the NO/cGMP signaling pathway.

Biologically active toxin from macroalgae Chaetomorpha antennina Bory, against the lepidopteran Spodoptera litura Fab. and evaluation of toxicity to earthworm, Eudrilus eugeniae Kinb

BackgroundSeaweeds harbour a wide array of bioactive compounds shown to be effective in support of sustainable agricultural practices. The green seaweed Chaetomorpha antennina found in abundance in coastal areas of India has been reported with various bioactivities. Owing to the requirement of alternative and economical natural pest control method to be applied in sustainable agronomic strategies, the current study attempts to evaluate the efficacy of chemical toxins from C. antennina, as insecticidal agents, by inspecting their effects on the physiology, biochemistry, immune system, and histology of one of the most important insect pests of agricultural crops in the Asian tropics, the polyphagous lepidopteran Spodoptera litura.ResultsThe active fraction 5 isolated from C. antennina using methanol extraction produced significant mortality rates of S. litura among all the other fractions obtained. GC–MS analysis revealed the presence of various pesticide compounds. The toxin compounds (active fraction 5) were found to negatively influence the pest’s immune system performance at sub-lethal concentrations (LC50 38.73and LC90 53.60 ppm), affecting insect development, reducing the haemocyte count (69.24%) and reduced the activity of major defence enzyme phenoloxidase decreased post-treatments. Digestive phosphatase enzymes, acid phosphatase, ACP, alkaline phosphatase, ALP, and ATPase were demodulated by 37.5, 39, and 23.9% compared with untreated. Increase in detoxification enzymes coupled with mid-gut collapse are indicative of the toxicity of the compounds. Earthworms exposed to seaweed compounds displayed no debarring effects.ConclusionExtracted seaweed compounds produced significant lethal effect on the insect larvae, affecting the immune as well as digestive systems of the pest. However, no such toxicity was observed in earthworms treated with the seaweed fraction supporting their environmentally benign nature. Since the insect immune system is responsible for the development of resurgence against pesticides, suppression of immunological activities by seaweed toxins indicate the long-term applicability of these compounds as prospective pesticides. The results support the potential of chemicals from C. antennina for biopesticide development to manage economically important agricultural pests.

The Toxins of Beauveria bassiana and the Strategies to Improve Their Virulence to Insects.

The long-term and excessive usage of pesticides is an enormous burden on the environment, which also increases pest resistance. To overcome this problem, research and application of entomopathogenic fungi, which are both environmentally friendly and cause lower resistance, have gained great momentum. Entomopathogenic fungi have a wide range of prospects. Apart from Bacillus thuringiensis, Beauveria bassiana is the most studied biopesticide. After invading insect hosts, B. bassiana produces a variety of toxins, which are secondary metabolites such as beauvericin, bassianin, bassianolide, beauverolides, tenellin, oosporein, and oxalic acid. These toxins help B. bassiana to parasitize and kill the hosts. This review unequivocally considers beauveria toxins highly promising and summarizes their attack mechanism(s) on the host insect immune system. Genetic engineering strategies to improve toxin principles, genes, or virulent molecules of B. bassiana have also been discussed. Lastly, we discuss the future perspective of Beauveria toxin research, including newly discovered toxins.

Fungal α-1,3-Glucan as a New Pathogen-Associated Molecular Pattern in the Insect Model Host Galleria mellonella.

Recognition of pathogen-associated molecular patterns (PAMPs) by appropriate pattern recognition receptors (PRRs) is a key step in activating the host immune response. The role of a fungal PAMP is attributed to β-1,3-glucan. The role of α-1,3-glucan, another fungal cell wall polysaccharide, in modulating the host immune response is not clear. This work investigates the potential of α-1,3-glucan as a fungal PAMP by analyzing the humoral immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan. We demonstrated that 57-kDa and 61-kDa hemolymph proteins, identified as β-1,3-glucan recognition proteins, bound to A. niger α-1,3-glucan. Other hemolymph proteins, i.e., apolipophorin I, apolipophorin II, prophenoloxidase, phenoloxidase activating factor, arylphorin, and serine protease, were also identified among α-1,3-glucan-interacting proteins. In response to α-1,3-glucan, a 4.5-fold and 3-fold increase in the gene expression of antifungal peptides galiomicin and gallerimycin was demonstrated, respectively. The significant increase in the level of five defense peptides, including galiomicin, corresponded well with the highest antifungal activity in hemolymph. Our results indicate that A. niger α-1,3-glucan is recognized by the insect immune system, and immune response is triggered by this cell wall component. Thus, the role of a fungal PAMP for α-1,3-glucan can be postulated.

Photorhabdus spp.: An Overview of the Beneficial Aspects of Mutualistic Bacteria of Insecticidal Nematodes.

The current approaches to sustainable agricultural development aspire to use safer means to control pests and pathogens. Photorhabdus bacteria that are insecticidal symbionts of entomopathogenic nematodes in the genus Heterorhabditis can provide such a service with a treasure trove of insecticidal compounds and an ability to cope with the insect immune system. This review highlights the need of Photorhabdus-derived insecticidal, fungicidal, pharmaceutical, parasiticidal, antimicrobial, and toxic materials to fit into current, or emerging, holistic strategies, mainly for managing plant pests and pathogens. The widespread use of these bacteria, however, has been slow, due to cost, natural presence within the uneven distribution of their nematode partners, and problems with trait stability during in vitro culture. Yet, progress has been made, showing an ability to overcome these obstacles via offering affordable mass production and mastered genome sequencing, while detecting more of their beneficial bacterial species/strains. Their high pathogenicity to a wide range of arthropods, efficiency against diseases, and versatility, suggest future promising industrial products. The many useful properties of these bacteria can facilitate their integration with other pest/disease management tactics for crop protection.

Insecticidal effect of garlic essential oil on Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) eggs

Studies have reported the resurgence of insect pests that are resistant to chemical and, more recently, to biological pesticides. Diatraea saccharalis is one of the main pests in sugarcane crops and responsible for large losses in the sugar and alcohol industries. The use of plant extracts including garlic essential oil (Allium sativum) which contains allicin, a compound that interferes with biochemical and physiological factors of target insects is considered an efficient and sustainable alternative for integrated pest management. The objective of this study was to test the toxicity of garlic essential oil on D. saccharalis eggs by analyzing rates of unhatched eggs, changes in external morphology, and esterases profile, enzymes related to insect resistance. For this, 24, 48, and 72-h-old eggs were immersed in 0.1, 0.5, and 1% garlic essential oil solutions for 2 min. Observations on embryonic development were made every 24-h for 72-h. Data on unhatched eggs were collected 288-h after treatments. For the esterases profile, eggs at 24-h after treatment with 1% solution were used. Eggs at 24-h-old, showed the least resistance to bioinsecticide, being that, 24-h after treatments with solutions 0.1, 0.5, and 1%, unhatched rates 80, 91.7, and 89.2%, respectively. The absence of embryos, ruptures, and protrusions on the chorionic region, and partial inhibition of EST-9, 10, and 11 were observed 24-h after the bioassays. These results demonstrate that garlic essential oil affects D. saccharalis eggs, partially inhibiting enzymes related to the insect immune system and can be used as a sustainable alternative for the integrated management of this insect pest.

Effect of Short-Term Desiccation, Recovery Time, and CAPA-PVK Neuropeptide on the Immune System of the Burying Beetle Nicrophorus vespilloides.

Environmental conditions, especially related to winter, are crucial for shaping activity of insect immune system. However, our previous research clearly indicates differences in the immune system functioning when the cold stress was induced in the laboratory conditions and when the beetles were collected from natural environment during winter. This is probably related to the multiplication of observed effects by simultaneous presence of different stress factors characteristic of winter, including desiccation. For these reasons, our next step was analysis of the effects of short-term desiccation and recovery time on the functioning of immune system of burying beetle Nicrophorus vespilloides. Also, the effect of Tenmo–PVK-2 (tenebrionid periviscerokinin), member of the CAPA–PVK neuropeptide family, was investigated to better understand observed changes. Short-term desiccation decreases the phagocytic activity of burying beetle haemocytes, which is correlated with a reduction in their adhesive ability. On the other hand, there was a significant increase in phenoloxidase (PO) activity and the level of proPO expression, which may suggest sealing the cuticula by melanin deposition and prevention of water loss. Additionally, the elevated level of defensin expression may be associated with the cross-talk between mechanisms, which participate in insect response to environmental stress, including pathogen infection. After 1 h of recovery time, the activity of tested cellular and humoral mechanisms was mostly back to the control level. However, inhibition of the activity of PO and down-regulation of proPO were noted. These results also indicate importance of melanin deposition during water loss. Moreover, it suggests that some changes in immune system functioning during stress conditions do not have an immune function. Interestingly, part of the effects characteristic of recovery time were also observed after the application of Tenmo–PVK-2, mainly related to haemocyte morphology. These results indicate that CAPA–PVK neuropeptides may also influence on activity of burying beetle immune system. It should be also highlighted that, because of the study of the effects of CAPA–PVK neuropeptides, homologs of vertebrate neuromedin U, the results may be interesting for search evolutionary similarities in the functioning of the neuroendocrine system of insects and vertebrates.

Vitellogenin in the honey bee midgut

The alimentary canal carries out many functions critical to insect physiology, including digesting and absorbing nutrients and water, housing beneficial gut bacteria, and eliciting immunological responses. The midgut, in particular, is a compartment for digestion and absorption and serves as a first point of contact between ingested pathogens and the insect immune system. Recently, we found the protein vitellogenin (Vg) localized in midgut cells of some honey bee workers. Vg is an important egg-yolk precursor protein in nearly all oviparous animals, but it also has immunological functions shared across many taxa. Additional and unexpected Vg functions have been characterized in honey bees, but none of these functions involve the midgut directly. Therefore, we sought to map out how Vg is localized and expressed in this organ across the two most common worker bee behavioral groups, namely nurses and foragers. We used immunohistochemistry and quantitative reverse transcription PCR to show Vg has different localization patterns in nurses and foragers and limited gene expression. Our study provides a platform for building a more detailed understanding of the possible roles of Vg in insect midgut cells, and it adds to the current knowledge of this fascinating, multi-functional protein.

Insect Behavioral Change and the Potential Contributions of Neuroinflammation-A Call for Future Research.

Many organisms are able to elicit behavioral change in other organisms. Examples include different microbes (e.g., viruses and fungi), parasites (e.g., hairworms and trematodes), and parasitoid wasps. In most cases, the mechanisms underlying host behavioral change remain relatively unclear. There is a growing body of literature linking alterations in immune signaling with neuron health, communication, and function; however, there is a paucity of data detailing the effects of altered neuroimmune signaling on insect neuron function and how glial cells may contribute toward neuron dysregulation. It is important to consider the potential impacts of altered neuroimmune communication on host behavior and reflect on its potential role as an important tool in the “neuro-engineer” toolkit. In this review, we examine what is known about the relationships between the insect immune and nervous systems. We highlight organisms that are able to influence insect behavior and discuss possible mechanisms of behavioral manipulation, including potentially dysregulated neuroimmune communication. We close by identifying opportunities for integrating research in insect innate immunity, glial cell physiology, and neurobiology in the investigation of behavioral manipulation.

Changes in haemolymph parameters and insect ability to respond to immune challenge during overwintering.

Overwintering is a challenging period in the life of temperate insects. A limited energy budget characteristic of this period can result in reduced investment in immune system. Here, we investigated selected physiological and immunological parameters in laboratory‐reared and field‐collected harlequin ladybirds (Harmonia axyridis). For laboratory‐reared beetles, we focused on the effects of winter temperature regime (cold, average, or warm winter) on total haemocyte concentration aiming to investigate potential effects of ongoing climate change on immune system in overwintering insects. We recorded strong reduction in haemocyte concentration during winter; however, there were only limited effects of winter temperature regime on changes in haemocyte concentration in the course of overwintering. For field‐collected beetles, we measured additional parameters, specifically: total protein concentration, antimicrobial activity against Escherichia coli, and haemocyte concentration before and after overwintering. The field experiment did not investigate effects of winter temperature, but focused on changes in inducibility of insect immune system during overwintering, that is, measured parameters were compared between naïve beetles and those challenged by Escherichia coli. Haemocyte concentration decreased during overwintering, but only in individuals challenged by Escherichia coli. Prior to overwintering, the challenged beetles had a significantly higher haemocyte concentration compared to naïve beetles, whereas no difference was observed after overwintering. A similar pattern was observed also for antimicrobial activity against Escherichia coli as challenged beetles outperformed naïve beetles before overwintering, but not after winter. In both sexes, total protein concentration increased in the course of overwintering, but females had a significantly higher total protein concentration in their hemolymph compared to males. In general, our results revealed that insect’s ability to respond to an immune challenge is significantly reduced in the course of overwintering.

A possible role of tachykinin-related peptide on an immune system activity of mealworm beetle, Tenebrio molitor L.

Tachykinin-related peptides (TRPs) are important neuropeptides. Here we show that they affect the insect immune system, especially the cellular response. We also identify and predict the sequence and structure of the tachykinin-related peptide receptor (TRPR) and confirm the presence of expression of gene encoding TRPR on Tenebrio molitor haemocytes.After application of the Tenmo-TRP-7 in T. molitor the number of circulating haemocytes increased and the number of haemocytes participating in phagocytosis of latex beads decreased in a dose- and time-dependent fashion. Also, Tenmo-TRP-7 affects the adhesion ability of haemocytes. Six hours after injection of Tenmo-TRP-7, a decrease of haemocyte surface area was observed under both tested Tenmo-TRP-7 concentrations (10−7 and 10−5 M). The opposite effect was reported 24 h after injection, which indicates that the influence of Tenmo-TRP-7 on modulation of haemocyte behaviour differs at different stages of stress response. Tenmo-TRP-7 application also resulted in increased phenoloxidase activity 6 and 24 h after injection.The assessment of DNA integrity of haemocytes showed that the injection of Tenmo-TRP-7 at 10−7 M led to a decrease in DNA damage compared to control individuals. This effect was only visible 6 h after Tenmo-TRP-7 application. After 24 h, Tenmo-TRP-7 injection increased DNA damage.We also confirmed the expression of immune-related genes in nervous tissue of T. molitor. Transcripts for genes encoding receptors participating in pathogen recognition processes and antimicrobial peptides were detected in T. molitor brain, retrocerebral complex and ventral nerve cord. These results may indicate a role of the insect nervous system in pathogen recognition and modulation of immune response similar to vertebrates.Taken together, our results support the notion that tachykinin-related peptides probably play an important role in the regulation of the insect immune system. Moreover, some resemblances with action of tachykinin-related peptides and substance P showed that insects can be potential model organisms for analysis of hormonal regulation of conserved innate immune mechanisms.

Insect Immune Evasion by Dauer and Nondauer Entomopathogenic Nematodes.

The immune response of animals, including insects, is overcome by some parasites. For example, dauer larvae (DL) of the obligate entomopathogenic nematodes (EPNs) Heterorhabditis and Steinernema can invade insects, evade their defenses, and cause death. Although DL were long assumed to be the only infective stage of nematodes, recent reports suggest that L2-L3 larvae of facultative EPNs are also capable of killing insects. There are no studies, to our knowledge, about the role of nonimmunological barriers (the exoskeleton and its openings) in avoiding infection by DL and L2-L3 larvae, or whether these larval stages evade the host immune system in the same way. The objective of this study was to examine these questions by infecting Galleria mellonella with the facultative parasitic nematode Rhabditis regina. DL or L2-L3 larvae were either deposited on or near the moths or injected into their hemocoel. Once nematodes reached the hemocoel, the following host immune response parameters were quantified: prophenoloxidase, phenoloxidase, lytic activity, and the number of granular hemocytes. DL showed a greater ability to penetrate the exoskeleton than L2-L3 larvae. Once inside, however, both went unnoticed by the immune system and killed the insect. A higher number of granular hemocytes was activated by L2-L3 larvae than DL. We show for the first time that L2-L3 larvae can penetrate and evade the insect immune system. Further research is needed to compare facultative and specialized EPNs to determine which is more likely, with both DL and L2-L3 larvae, to evade insect defense barriers and produce death. The results will contribute to understanding the evolution of virulence in entomopathogenic nematodes.

Antimicrobial peptides are not involved in Plutella xylostella resistance to Cry1Ac

AbstractPrevious studies on Bacillus thuringiensis (Bt) resistance in the diamondback moth (DBM) Plutella xylostella have often focused on receptor proteins in the gut. In recent years, many studies have indicated that insect resistance to Bt is related to the immune system. Moreover, our group demonstrated that the expression of peptidoglycan recognition protein (PGRP) genes, which are located upstream of the insect humoral immune system signalling pathway, is significantly different between Cry1Ac‐resistant and Cry1Ac‐susceptible strains of DBM. Thus, whether antimicrobial peptides (AMPs), which are the major downstream effectors of the insect humoral immune system signalling pathway, are also related to the resistance of DBMs to Bt is a question worthy of in‐depth study. In the present study, we sought to (a) clone the CDS of AMP genes expressed in DBMs and (b) explore the effect of the cloned AMPs on the biological characteristics and Bt resistance of DBMs. Here, we revealed three kinds of AMPs (PxDef, PxMor and PxCec), and each of their full‐length CDSs was cloned. The recombinant PxDef, PxMor or PxCec proteins, which were expressed in a prokaryotic expression system, have a significant protective effect on DBMs in response to the complex microbial environment of the outside world but have no significant effect on the resistance of DBMs to Cry1Ac toxin. We believe that AMPs are not suitable as the primary entry point for studying the relationship between the immune system of DBMs and their resistance to Bt. This result will enable investigation of breakthrough ideas for further elucidating the mechanism of Bt impact on the insect immune system.

Identification and analysis of two lebocins in the oriental armyworm Mythimna separata

The insect immune system can produce defensive molecules, such as antimicrobial peptides (AMPs), to eliminate invading pathogens. Here, we report the identification of two cDNAs (MseLeb1, MseLeb2) that encode lepidopteral lebocin preproproteins in the oriental armyworm, Mythimna separata. Their open reading frames are 483/492 bp that encode 161/164 aa peptides. MseLeb1 is mainly expressed in the fat body and epidermis, while MseLeb2 is mainly expressed in the fat body, Malpighian tube, and epidermis. They were significantly induced by Escherichia coli, Staphylococcus aureus, and Beauveria bassiana in hemocytes. The preproproteins can be processed after RXXR motifs into mature peptides. Multiple sequence alignment indicates that MseLeb1 (18–42, 121–161) are potentially active peptides. Five peptides were synthesized for analyses: 18–42, 121–161, 121–154, 121–151, 121–146. Synthetic peptides showed agglutinating activity, but no hemolytic activity. Bacterial growth assay, colony formation assay, and electron microscopy revealed that synthetic peptides can inhibit bacterial growth and disrupt bacterial cell wall. B. bassiana conidia and blastospores were lysed by synthetic peptides. These results indicate that MseLeb1 and MseLeb2 are immune responsive lebocins, and the mature peptides have antibacterial and antifungal activities.

Activation of cellular immune response in insect model host Galleria mellonella by fungal α-1,3-glucan.

Alpha-1,3-glucan, in addition to β-1,3-glucan, is an important polysaccharide component of fungal cell walls. It is reported for many fungal species, including human pathogenic genera: Aspergillus, Blastomyces, Coccidioides, Cryptococcus, Histoplasma and Pneumocystis, plant pathogens, e.g. Magnaporthe oryzae and entomopathogens, e.g. Metarhizium acridum. In human and plant pathogenic fungi, α-1,3-glucan is considered as a shield for the β-1,3-glucan layer preventing recognition of the pathogen by the host. However, its role in induction of immune response is not clear. In the present study, the cellular immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan was investigated for the first time. The changes detected in the total hemocyte count (THC) and differential hemocyte count (DHC), formation of hemocyte aggregates and changes in apolipophorin III localization indicated activation of G. mellonella cellular mechanisms in response to immunization with A. niger α-1,3-glucan. Our results, which have clearly demonstrated the response of the insect immune system to this fungal cell wall component, will help in understanding the α-1,3-glucan role in immune response against fungal pathogens not only in insects but also in mammals, including humans.

Cloning and functional characterization of two peptidoglycan recognition protein isoforms (PGRP-LC) in Bactrocera dorsalis (Diptera: Tephritidae)

The innate immune system of insects is the front line of self-defense against pathogen invasion. Peptidoglycan recognition proteins (PGRPs) are important components and play key roles in insect immune systems by recognizing peptidoglycan (PGN) in bacterial cell walls. We characterized two isoforms of the PGRP-LC gene, BdPGRP-LCa and BdPGRP-LCb, from Bactrocera dorsalis (Hendel), an important fruit and vegetable pest worldwide. These two isoforms contain an open reading frames of 1 668 bp and 1 731 bp, encoding a protein of 555 and 576 amino acids, respectively. Quantitative real-time PCR results showed that both transcripts were prominently expressed in midgut and fat body of B. dorsalis adult. Inoculation of pathogens showed that both isoforms actively responded to Escherichia coli PGN. We also observed a light response to Staphylococcus aureus PGN. Upon Beauveria bassiana inoculation, the expression of BdPGRP-LCa was enhanced, but the expression of BdPGRP-LCb was suppressed. Suppression of both transcripts by RNA interference led to increased mortality of flies challenged by E. coli, indicating that the two isoforms are involved in sensing Gram-negative bacterial infections.

Immunological Function of the Antibacterial Peptide Attacin-Like in the Chinese Oak Silkworm, Antheraea pernyi

Antibacterial peptides play important roles in the innate immune system of insects and are divided into four categories according to their structures. Although many antibacterial peptides have been reported in lepidopteran insects, the roles of an attacin-like gene in immune response of Antheraea pernyi remain unclear. In this study, the cloning and immunological functions of an attacin-like gene from Antheraea pernyi were investigated. The open reading frame of Ap-attacin-like gene was cloned by PCR using the specific primers and then was ligated to the pET-32a vector to construct the recombinant plasmids Ap-attacin- like-pET-32a. The recombinant Ap-attacin-like protein was expressed in E. coli (BL21 DE3) cells and purified by Ni-NTA affinity chromatography. The expression patterns of Ap-attacin-like in different tissues or under microorganism challenges were investigated by real-time PCR and western blotting. Finally, agar well diffusion assay was performed to determine the antimicrobial activity of the recombinant Ap-attacin-like proteins based on the inhibition rate. The expression level of Ap-attacin-like was highest in the fat body compared with the other examined tissues. The expression of Ap-attacin-like in the fat body was significantly elevated after E. coli, Beauveria bassiana, Micrococcus luteus or Nuclear Polyhedrosis Virus challenges. In addition, the recombinant Ap-attacin-like proteins had obvious antibacterial activity against E. coli. Ap-attacin-like was highly expressed in immune-related tissues and its expression level was significantly induced by different microorganism challenges, suggesting that Ap-attacin-like participated in the innate immunity of A. pernyi.

Endocrine regulation of immunity in insects.

Organisms have constant contact with potentially harmful agents that can compromise their fitness. However, most of the times these agents fail to cause serious disease by virtue of the rapid and efficient immune responses elicited in the host that can range from behavioural adaptations to immune system triggering. The immune system of insects does not comprise the adaptive arm, making it less complex than that of vertebrates, but key aspects of the activation and regulation of innate immunity are conserved across different phyla. This is the case for the hormonal regulation of immunity as a part of the broad organismal responses to external conditions under different internal states. In insects, depending on the physiological circumstances, distinct hormones either enhance or suppress the immune response integrating individual (and often collective) responses physiologically and behaviourally. In this review, we provide an overview of our current knowledge on the endocrine regulation of immunity in insects, its mechanisms and implications on metabolic adaptation and behaviour. We highlight the importance of this multilayered regulation of immunity in survival and reproduction (fitness) and its dependence on the hormonal integration with other mechanisms and life-history traits.

Botanical extracts from Dodonaea viscosa (Sapindales: Sapindaceae) reduce hemocyte counts from Spodoptera exigua (Lepidoptera: Noctuidae) with potential insecticidal synergism with Isaria fumosorosea (Hypocreales: Cordycipitaceae)

ABSTRACT Some botanical extracts affect the cellular immune system of insects by interfering with normal hemocyte function. This gives rise to diminution in cellular immunity and causes a decrease in insect defense. This investigation evaluated the effect of acetonic (AcEDv) and methanolic (MeEDv) extracts of Dodonaea viscosa (1000, 2000, and 4000 ppm) on the total hemocyte count (THC) present in the hemolymph of Spodoptera exigua, as well as on its insecticidal activity, on its own and in combination with the entomopathogenic fungus Isaria fumosorosea. Water and Tween® were used as negative controls and Lorsban® as a positive control. Second instar S. exigua larvae were separately fed an artificial diet incorporating both extracts. THC was significantly lower in AcEDv treatment at 1000 ppm and MeEDv treatment at 1000 and 4000 ppm compared with negative controls. The insecticidal action of the individual extracts and those in combination with the conidia of I. fumosorosea manifested from day 21, while at day 28, the AcEDv at 1000 and 2000 ppm and the MeEDv at 4000 ppm applied with the fungus revealed mortality percentages higher than 50% and a significantly higher mortality compared with the negative controls. In conclusion, the extracts of D. viscosa reduced the total THC of S. exigua and suggest that the application of this plant extract presents a synergistic effect on the mortality of S. exigua exposed to entomopathogenic fungus I. fumosorosea.

Transcriptomics reveals specific molecular mechanisms underlying transgenerational immunity in Manduca sexta.

The traditional view of innate immunity in insects is that every exposure to a pathogen triggers an identical and appropriate immune response and that prior exposures to pathogens do not confer any protective (i.e., adaptive) effect against subsequent exposure to the same pathogen. This view has been challenged by experiments demonstrating that encounters with sublethal doses of a pathogen can prime the insect's immune system and, thus, have protective effects against future lethal doses. Immune priming has been reported across several insect species, including the red flour beetle, the honeycomb moth, the bumblebee, and the European honeybee, among others. Immune priming can also be transgenerational where the parent's pathogenic history influences the immune response of its offspring. Phenotypic evidence of transgenerational immune priming (TGIP) exists in the tobacco moth Manduca sexta where first‐instar progeny of mothers injected with the bacterium Serratia marcescens exhibited a significant increase of in vivo bacterial clearance. To identify the gene expression changes underlying TGIP in M. sexta, we performed transcriptome‐wide, transgenerational differential gene expression analysis on mothers and their offspring after mothers were exposed to S. marcescens. We are the first to perform transcriptome‐wide analysis of the gene expression changes associated with TGIP in this ecologically relevant model organism. We show that maternal exposure to both heat‐killed and live S. marcescens has strong and significant transgenerational impacts on gene expression patterns in their offspring, including upregulation of peptidoglycan recognition protein, toll‐like receptor 9, and the antimicrobial peptide cecropin.