Heat shock affects host-pathogen interaction in Galleria mellonella infected with Bacillus thuringiensis

Hotter days, stronger immunity? Exploring the impact of rising temperatures on insect gut health and microbial relationships

Climate change can generate cascading effects on animals through compounding stressors. As ectotherms, insects are particularly susceptible to variation in temperature and extreme events. How insects respond to temperature often occurs with respect to their environment, and a pertinent question involves how thermal stress integrates with insect capabilities to resolve interactions with gut microorganisms (microbiome and gut pathogens). We explore the impact of elevated temperatures and the impact of the host physiological response influencing immune system regulation and the gut microbiome. We summarize the literature involving how elevated temperature extremes impact insect gut immune systems, and how in turn that alters potential interactions with the gut microbiome and potential pathogens. Temperature effects on immunity are complex, and ultimate effects on microbial components can vary by system. Moreover, there are multiple questions yet to explore in how insects contend with simultaneous abiotic stressors and potential trade-offs in their response to opportunistic microbiota.

Environment-host-parasite interactions in mass-reared insects

The mass production of insects is rapidly expanding globally, supporting multiple industrial needs. However, parasite infections in insect mass-production systems can lower productivity and can lead to devastating losses. High rearing densities and artificial environmental conditions in mass-rearing facilities affect the insect hosts as well as their parasites. Environmental conditions such as temperature, gases, light, vibration, and ionizing radiation can affect productivity in insect mass-production facilities by altering insect development and susceptibility to parasites. This review explores the recent literature on environment-host-parasite interactions with a specific focus on mass-reared insect species. Understanding these complex interactions offers opportunities to optimise environmental conditions for the prevention of infectious diseases in mass-reared insects.

Tenuazonic acid alters immune and physiological reactions and susceptibility to pathogens in Galleria mellonella larvae

Tenuazonic acid (TeA) is synthesized by phytopathogenic and opportunistic fungi and is detected in a broad range of foods. This natural compound is of interest in terms of toxicity to animals, but its mechanisms of action on insects are poorly understood. We administered TeA orally at different concentrations (0.2-5.0 mg/[gram of a growth medium]) to the model insect Galleria mellonella, with subsequent estimation of physiological, histological, and immunological parameters in different tissues (midgut, fat body, and hemolymph). Susceptibility of the TeA-treated larvae to pathogenic microorganisms Beauveria bassiana and Bacillus thuringiensis was also analyzed. The feeding of TeA to the larvae led to a substation delay of larval growth, apoptosis-like changes in midgut cells, and an increase in midgut bacterial load. A decrease in activities of detoxification enzymes and downregulation of genes Nox, lysozyme, and cecropin in the midgut and/or hemocoel tissues were detected. By contrast, genes gloverin, gallerimycin, and galiomycin and phenoloxidase activity proved to be upregulated in the studied tissues. Hemocyte density did not change under the influence of TeA. TeA administration increased susceptibility of the larvae to B. bassiana but diminished their susceptibility to B. thuringiensis. The results indicate that TeA disturbs wax moth gut physiology and immunity and also exerts a systemic action on this insect. Mechanisms underlying the observed changes in wax moth susceptibility to the pathogens are discussed.

Cationic protein 8 plays multiple roles in Galleria mellonella immunity

Galleria mellonella cationic protein 8 (GmCP8) is a hemolymph protein previously identified as an opsonin and an inhibitor of fungal proteases. In this work, we showed its bactericidal activity toward Pseudomonas entomophila, Pseudomonas aeruginosa, Bacillus thuringiensis, Staphylococcus aureus, and Escherichia coli and against yeast-like fungi Candida albicans. The activity against E. coli was correlated with bacterial membrane permeabilization. In turn, in the case of P. entomophila, B. thuringiensis, and C. albicans, the atomic force microscopy analysis of the microbial surface showed changes in the topography of cells and changes in their nanomechanical properties. GmCP8 also showed the inhibitory activity toward the serine protease trypsin and the metalloproteinase thermolysin. The expression of the gene encoding the GmCP8 protein did not increase either in the gut or in the fat body of G. mellonella after oral infection with P. entomophila. Similarly, the amount of GmCP8 in the hemolymph of G. mellonella did not change in immune-challenged insects. However, when GmCP8 was injected into the G. mellonella hemocel, a change in the survival curve was observed in the infected larvae. Our results shed new light on the function of GmCP8 protein in insect immunity, indicating its role in humoral defence mechanisms.

Hormesis and insects: Effects and interactions in agroecosystems

Insects in agroecosystems contend with many stressors - e.g., chemicals, heat, nutrient deprivation - that are often encountered at low levels. Exposure to mild stress is now well known to induce hormetic (stimulatory) effects in insects, with implications for insect management, and ecological structure and function in agroecosystems. In this review, we examine the major ecological niches insects occupy or guilds to which they belong in agroecosystems and how hormesis can manifest within and across these groups. The mechanistic underpinnings of hormesis in insects are starting to become established, explaining the many phenotypic hormetic responses observed in insect reproduction, development, and behavior. Whereas potential effects on insect populations are well supported in laboratory experiments, field-based hypothesis-driven research on hormesis is greatly lacking. Furthermore, because most ecological paradigms are founded within the context of communities, entomological agroecologists interested in hormesis need to 'level up' and test hypotheses that explore effects on species interactions, and community structure and functioning. Embedded in this charge is to continue experimentation on herbivorous pest species while shifting more focus towards insect natural enemies, pollinators, and detritivores - guilds that play crucial roles in highly functioning agroecosystems that have been understudied in hormesis research. Important areas for future insect agroecology research on hormesis are discussed.

Does Bacillus thuringiensis Affect the Stress and Immune Responses of Rhynchophorus ferrugineus Larvae, Females, and Males in the Same Way?

Simple Summary

Rhynchophorus ferrugineus is a destructive quarantine pest of palm trees, now widely distributed. Although broad-spectrum insecticides are often used to protect palm against R. ferrugineus, there is increasing concern about their effects on the environment and human health, especially where palm trees are located in urban areas. As an environmentally friendly entomopathogen, Bacillus thuringiensis (Bt) has been widely used to prevent other pest infestations. Although Bt products are the most sold bio-insecticides, there are still many interesting features to be investigated in the relationship of Bt and its hosts. We investigated the effect of Bt on larvae, females, and males. This research yielded experimental evidence of significant mortality and significant effects on immune system and stress answer. Within a few hours, stress due to Bt infection was detected in the hemocytes and in the brain providing better insights into the insect-pathogen interaction and highlighting the potential use of Bt in R. ferrugineus management.

Abstract

Bacillus thuringiensis (Bt) is considered a potentially useful entomopathogen against red palm weevil (RPW) Rhynchophorus ferrugineus. We compared the effects of Bt on mature larvae, females, and males. The pathogenicity of Bt was evaluated, estimating: Median Lethal Dose (LD₅₀), Median Lethal Time (LT₅₀), Total Hemocyte Count (THC), and Differential Hemocyte Counts (DHC), and the expression of the stress protein Heat Shock Protein 70 (Hsp 70) in hemocytes and the brain. Mortality exhibited a positive trend with the dosage and duration of exposure to Bt. Larvae were more susceptible than adults, and the LD₅₀ of females was almost double the value of that of the larvae. LT₅₀ value was higher for females than for males and larvae. Treatment with sub-lethal doses of Bt induced a decrease in THC in larvae, females, and males. In treated larvae, plasmatocytes decreased, while oenocytes and spherulocytes increased. In treated females, all types of hemocytes decreased, while in males the number of plasmatocytes decreased and granulocytes increased. We also registered the stress response directly on hemocytes showing that, already at 3 h after eating Bt, the expression of the stress protein Hsp 70 was modulated. This effect was also observed in brain tissue at 6 h after treatment. The results confirm that Bt treatment induces a pathogenic state in larvae and adults of both sexes, with effects after only a few hours from ingestion; however, the effects are different in magnitude and in type of target.

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.

Identification of the Ricin-B-Lectin LdRBLk in the Colorado Potato Beetle and an Analysis of Its Expression in Response to Fungal Infections

Ricin-B-lectins (RBLs) have been identified in many groups of organisms, including coleopterans insects, particularly the Colorado potato beetle Leptinotarsa decemlineata (LdRBLs). We hypothesized that one of these LdRBLs (LdRBLk) may be involved in the immune response to fungal infections. We performed a theoretical analysis of the structure of this protein. Additionally, the expression levels of the LdRBlk gene were measured in L. decemlineata in response to infections with the fungi Metarhizium robertsii and Beauveria bassiana. The expression levels of LdRBlk in the L. decemlineata cuticle and fat body were increased in response to both infections. The induction of LdRBlk expression was dependent on the susceptibility of larvae to the fungi. Upregulation of the LdRBlk gene was also observed in response to other stresses, particularly thermal burns. Elevation of LdRBlk expression was frequently observed to be correlated with the expression of the antimicrobial peptide attacin but was not correlated with hsp90 regulation. Commercially available β-lectin of ricin from Ricinuscommunis was observed to inhibit the germination of conidia of the fungi. We suggest that LdRBLk is involved in antifungal immune responses in the Colorado potato beetle, either exerting fungicidal properties directly or acting as a modulator of the immune response.

A comparison of the production of antimicrobial peptides and proteins by Galleria mellonella larvae in response to infection with two Pseudomonas aeruginosa strains differing in the profile of secreted proteases

The work presents identification of antimicrobial peptides and proteins (AMPs) in the hemolymph of Galleria mellonella larvae infected with two Pseudomonas aeruginosa strains (ATCC 27,853 and PA18), differing in the profile of secreted proteases. The insects were immunized with bacteria cultivated in rich (LB) and minimal (M9) media, which resulted in appearance of a similar broad set of AMPs in the hemolymph. Among them, 13 peptides and proteins were identified, i.e. proline-rich peptides 1 and 2, lebocin-like anionic peptide 1 and anionic peptide 2, defensin/galiomicin, cecropin, cecropin D-like peptide, apolipophoricin, gallerimycin, moricin-like peptide B, lysozyme, apolipophorin III, and superoxide dismutase. Bacterial strain- and/or medium-dependent changes in the level of proline-rich peptide 1, anionic peptide 1 and 2, moricin-like peptide B, cecropin D-like and gallerimycin were observed. The analysis of the expression of genes encoding cecropin, gallerimycin, and galiomicin indicated that they were differently affected by the bacterial strain but mainly by the medium used for bacterial culture. The highest expression was found for the LB medium. In addition to the antibacterial and antifungal activity, proteolytic activity was detected in the hemolymph of the P. aeruginosa-infected insects. Based on these results and those presented in our previous reports, it can be postulated that the appearance of AMPs in G. mellonella hemolymph can be triggered not only by P. aeruginosa pathogen associated molecular patterns (PAMPs) but also by bacterial extracellular proteases secreted during infection. However, although there were no qualitative differences in the set of AMPs depending on the P. aeruginosa strain and medium, differences in the level of particular AMPs synthesized in response to the bacteria used were observed.

Immunological interactions of Chilo suppressalis Walker (Lepidoptera: Crambidae) with the native entomopathogenic fungi

Entomopathogenic fungi can attack many insect hosts and have been applied as the eco-friendly alternatives to synthetic chemicals for the control of pests. Insects have developed different defense systems encountering entomopathogens including humoral and cellular immune responses. In the present study, injection of some native entomopathogenic fungi to the Chilo suppressalis Walker larvae resulted in an enhancement of the cellular and antimicrobial defenses. The numbers of total and differential hemocytes increased rapidly in the first 3 and 6 h but those gradually reduced 12 and 24 h post-injections. The nodule formation and phenoloxidase activity increased at the time intervals after fungal infection. A similar trend was found in the transcription of antimicrobial peptides including attacin1 and 2, cecropin1 and 2, gallerimycin, defensin, lysozyme, and prophenoloxidase-activating proteinase-3 during infection fungi. In all cases, the target gene transcription was upper in the larvae injected by the fungi than that of control larvae. These results may elucidate better knowledge on the interaction of the fungi present in agroecosystems with the target insect pest.

Galleria mellonella larvae exhibit a weight-dependent lethal median dose when infected with methicillin-resistant Staphylococcus aureus

Galleria mellonella is a recognised model to study antimicrobial efficacy; however, standardisation across the scientific field and investigations of methodological components are needed. Here, we investigate the impact of weight on mortality following infection with Methicillin-resistant Staphylococcus aureus (MRSA). Larvae were separated into six weight groups (180-300 mg at 20 mg intervals) and infected with a range of doses of MRSA to determine the 50% lethal dose (LD50), and the 'lipid weight' of larvae post-infection was quantified. A model of LD50 values correlated with weight was developed. The LD50 values, as estimated by our model, were further tested in vivo to prove our model. We establish a weight-dependent LD50 in larvae against MRSA and demonstrate that G. mellonella is a stable model within 180-260 mg. We present multiple linear models correlating weight with: LD50, lipid weight, and larval length. We demonstrate that the lipid weight is reduced as a result of MRSA infection, identifying a potentially new measure in which to understand the immune response. Finally, we demonstrate that larval length can be a reasonable proxy for weight. Refining the methodologies in which to handle and design experiments involving G. mellonella, we can improve the reliability of this powerful model.

Heat stress during development affects immunocompetence in workers, queens and drones of Africanized honey bees (Apis mellifera L.) (Hymenoptera: Apidae)

Though social insects generally seem to have a reduced individual immunoresponse compared to solitary species, the impact of heat stress on that response has not been studied. In the honey bee, the effect of heat stress on reproductives (queens and males/drones) may also vary compared to workers, but this is currently unknown. Here, we quantified the activity of an enzyme linked to the immune response in insects and known to be affected by heat stress in solitary species: phenoloxidase (PO), in workers, queens and drones of Africanized honey bees (AHBs) experimentally subjected to elevated temperatures during the pupal stage. Additionally, we evaluated this marker in individuals experimentally infected with the entomopathogenic fungus Metarhizium anisopliae. Differences in PO activity were found between sexes and castes, with PO activity generally higher in workers and lower in reproductives. Such differences are associated with the likelihood of exposure to infection and the role of different individuals in the colony. Contrary to our expectation, heat stress did not cause an increase in PO activity equally in all classes of individual. Heat stress during the pupal stage significantly decreased the PO activity of AHB queens, but not that of workers or drones, which more frequently engage in extranidal activity. Experimental infection with Metarhizium anisopliae reduced PO activity in queens and workers, but increased it in drones. Notably, heat stressed workers lived significantly shorter after infection despite exhibiting greater PO activity than queens or drones. We suggest that this discrepancy may be related to trade-offs among immune response cascades in honey bees such as between heat shock proteins and defensin peptides used in microbial defence. Our results provide evidence for complex relationships among humoral immune responses in AHBs and suggest that heat stress could result in a reduced life expectancy of individuals.

Immune response of Galleria mellonella after injection with non-lethal and lethal dosages of Candida albicans

The immune response of Galleria mellonella to injection with non-lethal and lethal dosages of Candida albicans was compared. Larvae infected with the non-lethal dosage (2 × 10⁴ cells/larva) did not show significant morphological changes, while those infected with the lethal dosage (2 × 10⁵ cells/larva) showed inhibition of motility and cocoon formation and became darker around the area of injection after 24 h. While the administration of the lower dosage caused approx. 5- and 20-fold induction of genes for gallerimycin and galiomycin, respectively, the injection with the higher dosage induced approx. 25 and 120-fold expression of the respective genes. Similar differences were obtained for the insect metalloproteinase inhibitor (IMPI) and hemolin gene transcripts. The relatively low level of immune gene expression was confirmed by an assay of hemolymph antifungal activity, which was detected only in larvae infected with lethal dosage of C. albicans. Furthermore, greater amounts of immune-inducible peptides were detected in the hemolymph extracts in the same group of larvae. The stronger humoral immune response was not correlated with survival. Phenol oxidase (PO) activity was induced only in the hemolymph of larvae infected with the non-lethal dose; injection of the lethal dose resulted in strong inhibition of this enzyme after 24 h. We showed that PO is susceptible to regulation by immune priming with the non-lethal dose of C. albicans. The activity of this enzyme was enhanced in primed larvae at the time of re-injection. When both primed and non-primed larvae received 2 × 10⁵ cells, the inhibition of PO was stronger in the primed group. G. mellonella infected with the lethal dose of C. albicans died despite the strong induction of humoral defence mechanisms. The priming-enhanced activity of PO was correlated with increased resistance to subsequent infection.

Insect Defense Proteins and Peptides

The composition of insect hemolymph can change depending on many factors, e.g. access to nutrients, stress conditions, and current needs of the insect. In this chapter, insect immune-related polypeptides, which can be permanently or occasionally present in the hemolymph, are described. Their division into peptides or low-molecular weight proteins is not always determined by the length or secondary structure of a given molecule but also depends on the mode of action in insect immunity and, therefore, it is rather arbitrary. Antimicrobial peptides (AMPs) with their role in immunity, modes of action, and classification are presented in the chapter, followed by a short description of some examples: cecropins, moricins, defensins, proline- and glycine-rich peptides. Further, we will describe selected immune-related proteins that may participate in immune recognition, may possess direct antimicrobial properties, or can be involved in the modulation of insect immunity by both abiotic and biotic factors. We briefly cover Fibrinogen-Related Proteins (FREPs), Down Syndrome Cell Adhesion Molecules (Dscam), Hemolin, Lipophorins, Lysozyme, Insect Metalloproteinase Inhibitor (IMPI), and Heat Shock Proteins. The reader will obtain a partial picture presenting molecules participating in one of the most efficient immune strategies found in the animal world, which allow insects to inhabit all ecological land niches in the world.

Host-pathogen interactions upon the first and subsequent infection of Galleria mellonella with Candida albicans

Insects are able to develop enhanced resistance in response to repeated infection. This phenomenon is called immune priming. In this work, so-called "primed" Galleria mellonella larvae were re-infected with a lethal dose of Candida albicans 48 h after injection of a non-lethal dose, while "non-primed" larvae were infected only with a lethal dose. The increased resistance of the primed larvae correlated with a slower rate of body colonisation by the fungus. Changes in the protein profiles were detected in the whole hemolymph of the primed insects. The analysis of low-molecular weight proteins and peptides obtained with the use of three different organic solvents and comparative quantitative HPLC analysis thereof showed that the primed larvae did not have higher amounts of any infection-inducible polypeptides than the non-primed larvae. Moreover, electrophoresis of low-molecular weight polypeptides revealed an even lower level of immune-induced peptides in the primed larvae than in the non-primed ones. Furthermore, the defence activity of larval hemolymph, i.e. the antifungal, antibacterial, and lysozyme-type activity, was up-regulated in the primed larvae at the time of re-infection and, consequently, at the early time points after the infection with the lethal dose. Twenty four hours after the infection, these parameters were equally high in the non-primed and primed larvae. Accordingly, at the time of the injection of the lethal dose, certain immune-inducible genes were up-regulated. However, 24 h after the infection with the lethal dose, their expression in both groups was incomparably higher than at the time of the infection and, in most cases, it was as high in the primed larvae as in the non-primed ones. We found that only anti yeast-like activity was enhanced 24 h after the re-infection. This correlated with results obtained by testing the priming effect in heterologous systems: the primed animals did not exhibit higher resistance to the other pathogens tested.

Parasitoid envenomation alters the Galleria mellonella midgut microbiota and immunity, thereby promoting fungal infection

Gut bacteria influence the development of different pathologies caused by bacteria, fungi and parasitoids in insects. Wax moth larvae became more susceptible to fungal infections after envenomation by the ectoparasitoid Habrobracon hebetor. In addition, spontaneous bacterioses occurred more often in envenomated larvae. We analyzed alterations in the midgut microbiota and immunity of the wax moth in response to H. hebetor envenomation and topical fungal infection (Beauveria bassiana) alone or in combination using 16S rRNA sequencing, an analysis of cultivable bacteria and a qPCR analysis of immunity- and stress-related genes. Envenomation led to a predominance shift from enterococci to enterobacteria, an increase in CFUs and the upregulation of AMPs in wax moth midguts. Furthermore, mycosis nonsignificantly increased the abundance of enterobacteria and the expression of AMPs in the midgut. Combined treatment led to a significant increase in the abundance of Serratia and a greater upregulation of gloverin. The oral administration of predominant bacteria (Enterococcus faecalis, Enterobacter sp. and Serratia marcescens) to wax moth larvae synergistically increased fungal susceptibility. Thus, the activation of midgut immunity might prevent the bacterial decomposition of envenomated larvae, thus permitting the development of fungal infections. Moreover, changes in the midgut bacterial community may promote fungal killing.

Transgenerational Developmental Effects of Immune Priming in the Red Flour Beetle Tribolium castaneum

Immune priming, the increased chance to survive a secondary encounter with a pathogen, has been described for many invertebrate species, which lack the classical adaptive immune system of vertebrates. Priming can be specific even for closely related bacterial strains, last up to the entire lifespan of an individual, and in some species, it can also be transferred to the offspring and is then called transgenerational immune priming (TGIP). In the red flour beetle Tribolium castaneum, a pest of stored grains, TGIP has even been shown to be transferred paternally after injection of adult beetles with heat-killed Bacillus thuringiensis. Here we studied whether TGIP in T. castaneum is also transferred to the second filial generation, whether it can also occur after oral and injection priming of larvae and whether it has effects on offspring development. We found that paternal priming with B. thuringiensis does not only protect the first but also the second offspring generation. Also, fitness costs of the immune priming became apparent, when the first filial generation produced fewer offspring. Furthermore, we used two different routes of exposure to prime larvae, either by injecting them with heat-killed bacteria or orally feeding them B. thuringiensis spore culture supernatant. Neither of the parental larval priming methods led to any direct benefits regarding offspring resistance. However, the injections slowed down development of the injected individuals, while oral priming with both a pathogenic and a non-pathogenic strain of B. thuringiensis delayed offspring development. The long-lasting transgenerational nature of immune priming and its impact on offspring development indicate that potentially underlying epigenetic modifications might be stable over several generations. Therefore, this form of phenotypic plasticity might impact pest control and should be considered when using products of bacterial origin against insects.

Susceptibility to entomopathogens and modulation of basal immunity in two insect models at different temperatures

In this work, we analysed the efficacy of different commercial bio-insecticides (Steinernema feltiae, Steinernema carpocapsae, Heterorhabditis bacteriophora and Bacillus thuringiensis) by valuating the mortality induced on two insect models, Galleria mellonella (Lepidoptera) and Sarcophaga africa (Diptera) after exposure to different temperatures (10, 20 and 30 °C). Moreover, we investigated the effects of temperature on the basal humoral immunity of the two target insects; particularly, phenoloxidase (PO) and lysozyme activity. Our results show that G. mellonella is susceptible to all bio-insecticides at all the examined temperatures, except when infected at 10 °C with S. carpocapsae and at 30 °C with S. feltiae and B. thuringiensis. S. africa is more susceptible at 30 °C to all bioinsecticides; whereas, when infected at 10 and 20 °C, H. bacteriophora is the most efficient. Temperature modulates PO activity of both G. mellonella and S. africa, otherwise variations in lysozyme activity is observed only in G. mellonella. Except for a possible correlation between the increased lysozyme activity and the delayed Bt efficacy recorded on G. mellonella at 30 °C, a different resistance to bio-insecticides at different temperatures does not seem to be associated to variations of the host basal immunity, probably due to immunoevasive and immunodepressive strategies of these entomopathogens.

Evaluation of Cry1Ac and Cry2Aa Toxin Binding to Two Important Beneficial Cotton Field Insects, Harmonia axyridis and Orius similis

Transgenic crops expressing Cry toxins are effective and considered environmentally friendly alternatives to synthetic pesticides, but assessment of environmental risks of their application on nontarget organisms is ongoing. The main risk is the transfer of Cry toxins to natural enemies through the food chain. There is reported evidence supporting that Cry toxins can be detected in the body and gut of some natural enemy insects. Considering that binding of Cry toxins to insect proteins is an essential step in the intoxication process, this work was conducted to evaluate interactions between Cry1Ac and Cry2Aa toxins with proteins from larvae/nymphs and adults of two important predatory natural enemies in cotton fields, Harmonia axyridis and Orius similis. Results support the absence of Cry1Ac or Cry2Aa binding proteins in immature stages of H. axyridis and O. similis, as well as in imaginal stage of H. axyridis. One same binding band about 70 kDa was found in imaginal total protein of O. similis when probed with the two Cry proteins, with the best match to Hsc70 of O. sauteri in the Uniprot database. However, nonspecific binding was verified by following competitive binding assays between the two Cry proteins and imaginal total protein of O. similis. From these results, we may infer that Cry1Ac and Cry2Aa have no likely detrimental effects on H. axyridis and O. similis.

Fungal infection dynamics in response to temperature in the lepidopteran insect Galleria mellonella

This study examines how the dynamics of fungus-insect interactions can be modulated by temperature. The wax moth, Galleria mellonella, is a well-studied and important model insect whose larvae in the wild develop optimally at around 34 °C in beehives. However, surprisingly little research on wax moths has been conducted at relevant temperatures. In this study, the entomopathogenic fungus Metarhizium robertsii inflicted rapid and substantial mortality on wax moth larvae maintained at a constant temperature of 24 °C, but at 34 °C a 10 fold higher dose was required to achieve an equivalent mortality. The cooler temperature favored fungal pathogenicity, with condial adhesion to the cuticle, germination and hemocoel invasion all significantly enhanced at 24 °C, compared with 34 °C. The wax moth larvae immune responses altered with the temperature, and with the infective dose of the fungus. Enzyme-based immune defenses (lysozyme and phenoloxidase) exhibited enhanced activity at the warmer temperature. A dramatic upregulation in the basal expression of galiomicin and gallerimycin was triggered by cooling, and this was augmented in the presence of the fungus. Profiling of the predominant insect epicuticular fatty acids revealed a 4-7 fold increase in palmetic, oleic and linoleic acids in larvae maintained at 24 °C compared with those at 34 °C, but these failed to exert fungistatic effects on topically applied fungus. This study demonstrates the importance of choosing environmental conditions relevant to the habitat of the insect host when determining the dynamics and outcome of insect/fungus interactions, and has particular significance for the application of entomopathogens as biocontrol agents.

Stress Response Protein BolA Influences Fitness and Promotes Salmonella enterica Serovar Typhimurium Virulence

The intracellular pathogen Salmonella enterica serovar Typhimurium has emerged as a major cause of foodborne illness, representing a severe clinical and economic concern worldwide. The capacity of this pathogen to efficiently infect and survive inside the host depends on its ability to synchronize a complex network of virulence mechanisms. Therefore, the identification of new virulence determinants has become of paramount importance in the search of new targets for drug development. BolA-like proteins are widely conserved in all kingdoms of life. In Escherichia coli, this transcription factor has a critical regulatory role in several mechanisms that are tightly related to bacterial virulence. Therefore, in the present work we used the well-established infection model Galleria mellonella to evaluate the role of BolA protein in S Typhimurium virulence. We have shown that BolA is an important player in S Typhimurium pathogenesis. Specifically, the absence of BolA leads to a defective virulence capacity that is most likely related to the remarkable effect of this protein on S Typhimurium evasion of the cellular response. Furthermore, it was demonstrated that BolA has a critical role in bacterial survival under harsh conditions since BolA conferred protection against acidic and oxidative stress. Hence, we provide evidence that BolA is a determining factor in the ability of Salmonella to survive and overcome host defense mechanisms, and this is an important step in progress to an understanding of the pathways underlying bacterial virulence.IMPORTANCE BolA has been described as an important protein for survival in the late stages of bacterial growth and under harsh environmental conditions. High levels of BolA in stationary phase and under stresses have been connected with a plethora of phenotypes, strongly suggesting its important role as a master regulator. Here, we show that BolA is a determining factor in the ability of Salmonella to survive and overcome host defense mechanisms, and this is an important step in progress to an understanding of the pathways underlying bacterial virulence. This work constitutes a relevant step toward an understanding of the role of BolA protein and may have an important impact on future studies in other organisms. Therefore, this study is of utmost importance for understanding the genetic and molecular bases involved in the regulation of Salmonella virulence and may contribute to future industrial and public health care applications.

Bacterial and fungal infections induce bursts of dopamine in the haemolymph of the Colorado potato beetle Leptinotarsa decemlineata and greater wax moth Galleria mellonella

Dopamine (DA) is known as a hormone neurotrasnmitter molecule involved in several stress reactions in both vertebrates and invertebrates. Following infections with the fungi Metarhizium robertsii or Beauveria bassiana and the bacterium Bacillus thuringiensis, dopamine the concentration was measured at different time points in the haemolymph of the Colorado potato beetle, Leptinotarsa decemlineata and the larvae of the greater wax moth Galleria mellonella. The infection with M. robertsii increased (4 to 12-fold) DA concentrations in the haemolymph of the potato beetle larvae and the oral infection by B. thuringiensis also lead to a 30 and 45-fold increase. During infection of the greater wax moth larvae with Beauveria bassiana and B. thuringiensis DA increased 4 to 20-fold and about 2 to 2,5-fold respectively, compared to non-infected insects. The relative DA concentrations varied between the two insects and depended on the pathogens and post infection time.

Identification and evaluation of Galleria mellonella peptides with antileishmanial activity

Leishmaniasis is a neglected disease, World Health Organization (WHO) declared it as high priority worldwide. Colombia is one of the 98 countries in which the disease caused more than 17.000 cases per year. There is a need to explore novel therapies to reduce the side effects of the current treatments. For this reason, this study was aimed to evaluate Galleria mellonella hemolymph for potential peptides with anti-parasitic activity. Larvae were challenged with Leishmania (V) panamensis promastigotes and hemolymph was analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), reversed-phase chromatography (RP-HPLC), two-dimensional gel electrophoresis and liquid chromatography-mass spectroscopy (LC/MS). The immunological response of Galleria mellonella was followed by SDS-PAGE, immunized hemolymph was fractionated by RP-HPLC where fractions 5 and 11 showed the highest antileishmanial activity. From these fractions 15 spots were isolated by 2D gel electrophoresis and evaluated by LC/MS to identify the peptides present in the spots. After the analysis Moricin-B, Moricin-C4, Cecropin-D and Anionic Peptide 2 were identified due to the immune challenge with Leishmania promastigotes. Anionic peptide 2 and Cecropin-D were synthesized and evaluated for antileishmanial activity. The results showed that Anionic peptide 2 presented more anti-parasitic activity. This study showed for the first time the anti-parasitic potential of peptides derived from hemolymph of Galleria mellonella.

Regulatory Elements Located in the Upstream Region of the Rhizobium leguminosarum rosR Global Regulator Are Essential for Its Transcription and mRNA Stability

Rhizobium leguminosarum bv. trifolii is a soil bacterium capable of establishing a symbiotic relationship with clover (Trifolium spp.). Previously, the rosR gene, encoding a global regulatory protein involved in motility, synthesis of cell-surface components, and other cellular processes was identified and characterized in this bacterium. This gene possesses a long upstream region that contains several regulatory motifs, including inverted repeats (IRs) of different lengths. So far, the role of these motifs in the regulation of rosR transcription has not been elucidated in detail. In this study, we performed a functional analysis of these motifs using a set of transcriptional rosR-lacZ fusions that contain mutations in these regions. The levels of rosR transcription for different mutant variants were evaluated in R. leguminosarum using both quantitative real-time PCR and β-galactosidase activity assays. Moreover, the stability of wild type rosR transcripts and those with mutations in the regulatory motifs was determined using an RNA decay assay and plasmids with mutations in different IRs located in the 5′-untranslated region of the gene. The results show that transcription of rosR undergoes complex regulation, in which several regulatory elements located in the upstream region and some regulatory proteins are engaged. These include an upstream regulatory element, an extension of the -10 element containing three nucleotides TGn (TGn-extended -10 element), several IRs, and PraR repressor related to quorum sensing.

The heat shock response and humoral immune response are mutually antagonistic in honey bees

The honey bee is of paramount importance to humans in both agricultural and ecological settings. Honey bee colonies have suffered from increased attrition in recent years, stemming from complex interacting stresses. Defining common cellular stress responses elicited by these stressors represents a key step in understanding potential synergies. The proteostasis network is a highly conserved network of cellular stress responses involved in maintaining the homeostasis of protein production and function. Here, we have characterized the Heat Shock Response (HSR), one branch of this network, and found that its core components are conserved. In addition, exposing bees to elevated temperatures normally encountered by honey bees during typical activities results in robust HSR induction with increased expression of specific heat shock proteins that was variable across tissues. Surprisingly, we found that heat shock represses multiple immune genes in the abdomen and additionally showed that wounding the cuticle of the abdomen results in decreased expression of multiple HSR genes in proximal and distal tissues. This mutually antagonistic relationship between the HSR and immune activation is unique among invertebrates studied to date and may promote understanding of potential synergistic effects of disparate stresses in this critical pollinator and social insects more broadly.

Humoral immune response of Galleria mellonella after repeated infection with Bacillus thuringiensis

The insect immune system relies on innate mechanisms only. However, there is an increasing number of data reporting that previous immune challenge with microbial elicitors or a low number of microorganisms can modulate susceptibility after subsequent lethal infection with the same or different pathogen. This phenomenon is called immune priming. Its biochemical and molecular mechanisms remain unravelled. Here we present that Galleria mellonella larvae that survived infection induced by intrahemocelic injection of a low dose of Bacillus thuringiensis were more resistant to re-injection of a lethal dose of the same bacteria but not other bacteria and fungi tested. This correlated with enhanced activity detected in full hemolymph as well as in separated hemolymph polypeptides. In addition, we observed differences in the hemolymph protein pattern between primed and non-primed larvae after infection with the lethal dose of B. thuringiensis. Expression of genes encoding inducible defence molecules was not enhanced in the primed larvae after the infection with the lethal dose of B. thuringiensis. It is likely that priming affects the turnover of immune related hemolymph proteins; hence, upon repeated contact, the immune response may be more ergonomic.

Immunity of the greater wax moth Galleria mellonella

Investigation of insect immune mechanisms provides important information concerning innate immunity, which in many aspects is conserved in animals. This is one of the reasons why insects serve as model organisms to study virulence mechanisms of human pathogens. From the evolutionary point of view, we also learn a lot about host-pathogen interaction and adaptation of organisms to conditions of life. Additionally, insect-derived antibacterial and antifungal peptides and proteins are considered for their potential to be applied as alternatives to antibiotics. While Drosophila melanogaster is used to study the genetic aspect of insect immunity, Galleria mellonella serves as a good model for biochemical research. Given the size of the insect, it is possible to obtain easily hemolymph and other tissues as a source of many immune-relevant polypeptides. This review article summarizes our knowledge concerning G. mellonella immunity. The best-characterized immune-related proteins and peptides are recalled and their short characteristic is given. Some other proteins identified at the mRNA level are also mentioned. The infectious routes used by Galleria natural pathogens such as Bacillus thuringiensis and Beauveria bassiana are also described in the context of host-pathogen interaction. Finally, the plasticity of G. mellonella immune response influenced by abiotic and biotic factors is described.

The Galleria mellonella larvae as an in vivo model for evaluation of Shigella virulence

Shigella spp. causing bacterial diarrhea and dysentery are human enteroinvasive bacterial pathogens that are orally transmitted through contaminated food and water and cause bacillary dysentery. Although natural Shigella infections are restricted to humans and primates, several smaller animal models are used to analyze individual steps in pathogenesis. No animal model fully duplicates the human response and sustaining the models requires expensive animals, costly maintenance of animal facilities, veterinary services and approved animal protocols. This study proposes the development of the caterpillar larvae of Galleria mellonella as a simple, inexpensive, informative, and rapid in-vivo model for evaluating virulence and the interaction of Shigella with cells of the insect innate immunity. Virulent Shigella injected through the forelegs causes larvae death. The mortality rates were dependent on the Shigella strain, the infectious dose, and the presence of the virulence plasmid. Wild-type S. flexneri 2a, persisted and replicated within the larvae, resulting in haemocyte cell death, whereas plasmid-cured mutants were rapidly cleared. Histology of the infected larvae in conjunction with fluorescence, immunofluorescence, and transmission electron microscopy indicate that S. flexneri reside within a vacuole of the insect haemocytes that ultrastructurally resembles vacuoles described in studies with mouse and human macrophage cell lines. Some of these bacteria-laden vacuoles had double-membranes characteristic of autophagosomes. These results suggest that G. mellonella larvae can be used as an easy-to-use animal model to understand Shigella pathogenesis that requires none of the time and labor-consuming procedures typical of other systems.

Effect of stress on heat shock protein levels, immune response and survival to fungal infection of Mamestra brassicae larvae

Although the utilisation of fungal biological control agents to kill insect pests is desirable, it is known that the outcome of infection may be influenced by a number of criteria, including whether or not the target insect is stressed. In the current work, topical treatment of larvae of the lepidopteran pest, Mamestra brassicae, with conidia of Beauveria bassiana, followed by a heat stress (HS; 37°C for 1h) 48h later, resulted in a similar level of larval survival to that occurring for no heat stress (No-HS), fungus-treated larvae. By contrast, when the HS was applied 24h after fungal treatment, larval survival was significantly increased, indicating that the HS is protecting the larvae from B. bassiana. Similarly, exposure of larvae to a HS provided protection against Metarhizium brunneum (V275) at 48h (but not 24h) after fungal treatment. To elucidate the mechanism(s) that might contribute to HS-induced increases in larval survival against fungal infection, the effects of a HS on key cellular and humoral immune responses and on the level of selected heat shock proteins (HSP) were assessed. When larvae were kept under control (No HS) conditions, there was no significant difference in the haemocyte number per ml of haemolymph over a 24h period. However, exposure of larvae to a HS, significantly increased the haemocyte density immediately after (t=0h) and 4h after HS compared to the No HS controls, whilst it returned to control levels at t=24h. In addition, in vitro assays indicated that haemocytes harvested from larvae immediately after (0h) and 4h (but not 24h) after a HS exhibited higher rates of phagocytosis of FITC-labelled B. bassiana conidia compared to haemocytes harvested from non-HS larvae. Interestingly, the HS did not appear to increase anti-fungal activity in larval plasma. Western blot analysis using antibodies which cross react with Drosophila melanogaster HSP, resulted in a relatively strong signal for HSP 70 and HSP 90 from extracts of 50,000 and 100,000haemocytes, respectively, harvested from No-HS larvae. By contrast, for HSP 60, a lysate derived from 200,000haemocytes resulted in a relatively weak signal. When larvae were exposed to a HS, the level of all three HSP increased compared to the No HS control 4h and 16h after the HS. However, 24h after treatment, any heat stress-mediated increase in HSP levels was minimal and not consistently detected. Similar results were obtained when HSP 90, 70, and 60 levels were assessed in fat body harvested from heat stressed and non-heat stressed larvae. With regard to HSP 27, no signal was obtained even when a lysate from 200,000haemocytes or three times the amount of fat body were processed, suggesting that the anti-HSP 27 antibody utilised does not cross-react with the M. brassicae HSP. The results suggest that a HS-mediated increase in haemocyte density and phagocytic activity, together with an upregulation of HSP 90 and 70, may contribute to increasing the survival of M. brassicae larvae treated with B. bassiana and M. brunneum (V275).

Short-Term Heat Shock Affects Host-Virus Interaction in Mice Infected with Highly Pathogenic Avian Influenza Virus H5N1

Highly pathogenic avian influenza virus (HPAIV) H5N1 is a highly contagious virus that can cause acute respiratory infections and high human fatality ratio due to excessive inflammatory response. Short-term heat shock, as a stressful condition, could induce the expression of heat shock proteins that function as molecular chaperones to protect cells against multiple stresses. However, the protective effect of short-term heat shock in influenza infection is far from being understood. In this study, mice were treated at 39°C for 4 h before being infected with HPAIV H5N1. Interestingly, short-term heat shock significantly increased the levels of HSP70 and pro-inflammatory cytokines IL-6, TNF-α, IFN-β, and IFN-γ in the lung tissues of mice. Following HPAIV H5N1 infection, short-term heat shock alleviated immunopathology and viral replication in lung tissue and repressed the weight loss and increased the survival rate of H5N1-infected mice. Our data reported that short-term heat shock provided beneficial anti-HPAIV H5N1 properties in mice model, which offers an alternative strategy for non-drug prevention for influenza infection.

Galleria mellonella larvae are capable of sensing the extent of priming agent and mounting proportionatal cellular and humoral immune responses

Larvae of Galleria mellonella are useful models for studying the innate immunity of invertebrates or for evaluating the virulence of microbial pathogens. In this work, we demonstrated that prior exposure of G. mellonella larvae to high doses (1×10(4), 1×10(5) or 1×10(6) cells/larva) of heat-killed Photorhabdus luminescens TT01 increases the resistance of larvae to a lethal dose (50 cells/larva) of viable P. luminescens TT01 infection administered 48h later. We also found that the changes in immune protection level were highly correlated to the changes in levels of cellular and humoral immune parameters when priming the larvae with different doses of heat-killed P. luminescens TT01. Priming the larvae with high doses of heat-killed P. luminescens TT01 resulted in significant increases in the hemocytes activities of phagocytosis and encapsulation. High doses of heat-killed P. luminescens TT01 also induced an increase in total hemocyte count and a reduction in bacterial density within the larval hemocoel. Quantitative real-time PCR analysis showed that genes coding for cecropin and gallerimycin and galiomycin increased in expression after priming G. mellonella with heat-killed P. luminescens TT01. All the immune parameters changed in a dose-dependent manner. These results indicate that the insect immune system is capable of sensing the extent of priming agent and mounting a proportionate immune response.

Can poisons stimulate bees? Appreciating the potential of hormesis in bee-pesticide research

Hormesis, a biphasic dose response whereby exposure to low doses of a stressor can stimulate biological processes, has been reported in many organisms, including pest insects when they are exposed to low doses of a pesticide. However, awareness of the hormesis phenomenon seems to be limited among bee researchers, in spite of the increased emphasis of late on pollinator toxicology and risk assessment. In this commentary, we show that there are several examples in the literature of substances that are toxic to bees at high doses but stimulatory at low doses. Appreciation of the hormetic dose response by bee researchers will improve our fundamental understanding of how bees respond to low doses of chemical stressors, and may be useful in pollinator risk assessment.

Temperature-Related Reaction Norms of Gene Expression: Regulatory Architecture and Functional Implications

The environment has profound effects on the expression of many traits and reaction norms describe the expression dynamics of a trait across a broad range of environmental conditions. Here, we analyze gene expression in Drosophila melanogaster across four different developmental temperatures (13-29 °C). Gene expression is highly plastic with 83.3% of the genes being differentially expressed. We distinguished three components of plasticity: 1) Dynamics of gene expression intensity (sum of change), 2) direction of change, and 3) curvature of the reaction norm (linear vs. quadratic). Studying their regulatory architecture we found that all three plasticity components were most strongly affected by the number of different transcription factors (TFs) binding to the target gene. More TFs were found in genes with less expression changes across temperatures. Although the effect of microRNAs was weaker, we consistently noted a trend in the opposite direction. The most plastic genes were regulated by fewer TFs and more microRNAs than less plastic genes. Different patterns of plasticity were also reflected by their functional characterization based on gene ontology. Our results suggest that reaction norms provide an important key to understand the functional requirements of natural populations exposed to variable environmental conditions.

Changes in the hemolymph protein profiles in Galleria mellonella infected with Bacillus thuringiensis involve apolipophorin III. The effect of heat shock

This report concerns the effect of heat shock on host-pathogen interaction in Galleria mellonella infected with Bacillus thuringiensis. We show enhanced activity against Gram-positive bacteria in the hemolymph of larvae pre-exposed to heat shock before infection with B. thuringiensis. Heat shock influenced the protein pattern in the hemolymph of infected larvae: more peptides with a molecular weight below 10 kDa were detected in comparison with nonshocked animals. Additionally, we noticed that the amount of apolipophorin III (apoLp-III) in the hemolymph decreased transiently following infection, which was considerably higher in larvae pre-exposed to heat shock. On the other hand, its expression in the fat body showed a consequent infection-induced decline, observed equally in shocked and nonshocked animals. This suggests that the amount of apoLp-III in the hemolymph of G. mellonella larvae is regulated at multiple levels. We also report that this protein is more resistant to degradation in the hemolymph of larvae pre-exposed to heat shock in comparison to nonshocked larvae. Two-dimensional analysis revealed the presence of three isoforms of apoLp-III, all susceptible to proteolytic degradation. However, one of them was the most abundant, both in the protease-treated and untreated hemolymph. Taking into consideration that, in general, apoLp-III has a stimulative effect on different immune-related hemolymph proteins and peptides, the reported findings bring us closer to understanding the effect of heat shock on the resistance of G. mellonella to infection.