Effects of food quality on trade-offs among growth, immunity and survival in the greater wax moth Galleria mellonella

An improved method to assess the encapsulation response in arthropods

Ecoimmunology explores how ecological factors and evolutionary processes influence immune responses across various taxa and how immune responses trade-off with other traits. Studying immune responses requires biologically meaningful immunoassays applicable to a broad range of taxa and are sensitive enough to detect changes in the immune response. Useful immunoassays should also correlate with immunocompetence and fitness. The encapsulation response, a complex immune mechanism in arthropods, serves as a robust method for ecoimmunological investigations. However, traditional methods to test the encapsulation response can require long training. This study introduces an innovative, cost-effective method for assessing the encapsulation immune response in arthropods, which simplifies the procedure by reducing the training time and skill required. Our modified device utilizes a pen and syringe assembly for inserting monofilaments into arthropod larvae. We compared our device against traditional methods. Despite the new method being 22% faster, it did not compromise the accuracy or effectiveness of the encapsulation response when compared with traditional techniques, demonstrating similar degrees of melanization and encapsulation. Our method allowed for more accessible participation by less experienced researchers, such as undergraduates, facilitating their involvement in ecoimmunological research.

The complex interactions between nutrition, immunity and infection in insects

Insects are the most diverse animal group on the planet. Their success is reflected by the diversity of habitats in which they live. However, these habitats have undergone great changes in recent decades; understanding how these changes affect insect health and fitness is an important challenge for insect conservation. In this Review, we focus on the research that links the nutritional environment with infection and immune status in insects. We first discuss the research from the field of nutritional immunology, and we then investigate how factors such as intracellular and extracellular symbionts, sociality and transgenerational effects may interact with the connection between nutrition and immunity. We show that the interactions between nutrition and resistance can be highly specific to insect species and/or infection type - this is almost certainly due to the diversity of insect social interactions and life cycles, and the varied environments in which insects live. Hence, these connections cannot be easily generalised across insects. We finally suggest that other environmental aspects - such as the use of agrochemicals and climatic factors - might also influence the interaction between nutrition and resistance, and highlight how research on these is essential.

The Effects of Diet on the Immune Responses of the Oriental Armyworm Mythimna separata

Nutrients can greatly affect host immune defenses against infection. Possessing a simple immune system, insects have been widely used as models to address the relationships between nutrition and immunity. The effects of high versus low protein-to-carbohydrate ratio (P:C) diets on insect immune responses vary in different studies. To reveal the dietary manipulation of immune responses in the polyphagous agricultural pest oriental armyworm, we examined immune gene expression, phenoloxidase (PO) activity, and phagocytosis to investigate the immune traits of bacteria-challenged oriental armyworms, which were fed different P:C ratio diets. We found the oriental armyworms that were fed a 35:7 (P:C) diet showed higher phenoloxidase (PO) activity and stronger melanization, and those reared on a 28:14 (P:C) diet showed higher antimicrobial activity. However, different P:C diets had no apparent effect on the hemocyte number and phagocytosis. These results overall indicate that high P:C diets differently optimize humoral immune defense responses in oriental armyworms, i.e., PO-mediated melanization and antimicrobial peptide synthesis in response to bacteria challenge.

Insect Antimicrobial Peptides: Advancements, Enhancements and New Challenges

Several insects are known as vectors of a wide range of animal and human pathogens causing various diseases. However, they are also a source of different substances, such as the Antimicrobial Peptides (AMPs), which can be employed in the development of natural bioactive compounds for medical, veterinary and agricultural applications. It is well known that AMP activity, in contrast to most classical antibiotics, does not lead to the development of natural bacterial resistance, or at least the frequency of resistance is considered to be low. Therefore, there is a strong interest in assessing the efficacy of the various peptides known to date, identifying new compounds and evaluating possible solutions in order to increase their production. Moreover, implementing AMP modulation in insect rearing could preserve insect health in large-scale production. This review describes the current knowledge on insect AMPs, presenting the validated ones for the different insect orders. A brief description of their mechanism of action is reported with focus on proposed applications. The possible effects of insect diet on AMP translation and synthesis have been discussed.

Impact of the Diet on the Mortality and on Gene Expression of the Antimicrobial Peptide Tenecin 3 in Tenebrio molitor Larvae Infected by Beauveria bassiana

Large-scale insect rearing can be subjected to microbial infections, leading to serious economic losses. When possible, the use of antibiotics is to be avoided for insects intended as feed or food and new strategies to preserve the health of the farmed insects are required. The effectiveness of insect immune system depends on several factors, including the nutritional composition of the diet. The possibility to modulate immune responses through the diet is currently a topic of great interest from an application point of view. We evaluated the effect of two different diets on the survival rate and gene expression of the antimicrobial peptide Tenecin 3 in uninfected and Beauveria bassiana-infected Tenebrio molitor L. larvae. A wheat bran diet, mixed 50% with brewers' spent grains, could positively influence the expression of Tenecin 3 gene when uninfected T. molitor is allowed to develop on such a substrate from early larval stages. Even if, in our trial, the diet with added brewers' spent grains could not reduce the mortality of the larvae infected with B. bassiana, higher transcriptional levels of the antifungal peptide were observed in insects fed this diet, depending on the timing of diet administration.

Reaction of Cornu aspersum Immune System against Different Aelurostrongylus abstrusus Developmental Stages

Cornu aspersum, the land snail, is recognized as a suitable intermediate host of Aelurostrongylus abstrusus; however, there is little information both on larval development as well as on the intermediate host’s immune system reaction to the parasite. The aim of the study was to assess the histological reaction of C. aspersum’s immune system against A. abstrusus. Sixty-five snails were provided by a snail farm. Five of them were digested to assess the absence of natural parasitic infections. The remaining sixty were divided into five groups. Three groups of snails were infected with A. abstrusus using by-contact or injection methods; one group was injected only with saline solution and one group was left untreated as the control. The snails of group A were sacrificed and digested on study days 2, 10, and 18; snails of the other groups were collected and examined for histopathological analysis on study days 2, 10, and 18. On study day 2, in the infected snails, several free L1s were observed along with the absence of immune system reactions. On day 10, the L2s elicited an intense reaction in the internal layer of the muscular foot. On day 18, all L3s partially encapsulated by the snail’s immune system were observed in the outermost part of the muscular foot, which is near and among the goblet cells. This last finding suggests that L3s could be shed with the snail’s mucus and spread in the environment, representing an alternative route of transmission for this feline lungworm.

Immune Responses of the Black Soldier Fly Hermetia illucens (L.) (Diptera: Stratiomyidae) Reared on Catering Waste

The black soldier fly (BSF), Hermetia illucens L. (Diptera: Stratiomyidae), has a great bioconversion potential and ability to develop on diverse substrates. Although the use of catering waste and food by-products containing meat and fish would reduce the footprint of the insect sector, to date, in Europe, their use is still facing legal obstacles for insects as food and feed. Since a major request from the EU insect sector is to diversify the spectrum of allowed substrates, and considering that variations in diet composition could influence insect immune responses, we evaluated the impact of different catering wastes on BSF prepupae immunity. Insects were reared on five diets: one based on feed for laying hens and four based on catering waste containing (i) fruits and vegetables; (ii) fruits, vegetables and bread; (iii) fruit, vegetables, bread and dairy products; (iv) fruits, vegetables, bread, meat and fish. The gene expression of two antimicrobial peptides (AMPs), one defensin and one cecropin, was assessed. Moreover, the hemolymph inhibitory activity against Escherichia coli DH5α and Micrococcus yunnanensis HI55 was evaluated using diffusion assays in solid media. The up-regulation of both AMPs' encoding genes was observed in insects fed a bread-added and dairy product-added diet. All hemolymph samples showed inhibitory activity against both bacteria, affecting the colony size and number. The obtained results show how catering waste positively influences the H. illucens immune system. The possibility of modulating AMP expression levels through the diet opens up new perspectives in the management of insect health in mass rearings.

Insect Models in Nutrition Research

Insects are the most diverse organisms on earth, accounting for ~80% of all animals. They are valuable as model organisms, particularly in the context of genetics, development, behavior, neurobiology and evolutionary biology. Compared to other laboratory animals, insects are advantageous because they are inexpensive to house and breed in large numbers, making them suitable for high-throughput testing. They also have a short life cycle, facilitating the analysis of generational effects, and they fulfil the 3R principle (replacement, reduction and refinement). Many insect genomes have now been sequenced, highlighting their genetic and physiological similarities with humans. These factors also make insects favorable as whole-animal high-throughput models in nutritional research. In this review, we discuss the impact of insect models in nutritional science, focusing on studies investigating the role of nutrition in metabolic diseases and aging/longevity. We also consider food toxicology and the use of insects to study the gut microbiome. The benefits of insects as models to study the relationship between nutrition and biological markers of fitness and longevity can be exploited to improve human health.

Physiological stress and higher reproductive success in bumblebees are both associated with intensive agriculture

Free-living organisms face multiple stressors in their habitats, and habitat quality often affects development and life history traits. Increasing pressures of agricultural intensification have been shown to influence diversity and abundance of insect pollinators, and it may affect their elemental composition as well. We compared reproductive success, body concentration of carbon (C) and nitrogen (N), and C/N ratio, each considered as indicators of stress, in the buff-tailed bumblebee (Bombus terrestris). Bumblebee hives were placed in oilseed rape fields and semi-natural old apple orchards. Flowering season in oilseed rape fields was longer than that in apple orchards. Reproductive output was significantly higher in oilseed rape fields than in apple orchards, while the C/N ratio of queens and workers, an indicator of physiological stress, was lower in apple orchards, where bumblebees had significantly higher body N concentration. We concluded that a more productive habitat, oilseed rape fields, offers bumblebees more opportunities to increase their fitness than a more natural habitat, old apple orchards, which was achieved at the expense of physiological stress, evidenced as a significantly higher C/N ratio observed in bumblebees inhabiting oilseed rape fields.

Effect of host plant on the life history of the carnation tortrix moth Cacoecimorpha pronubana (Lepidoptera: Tortricidae)

The carnation tortrix moth, Cacoecimorpha pronubana (Hübner, [1799]) (Lepidoptera: Tortricidae), is one of the most economically important insect species affecting the horticultural industry in the UK. The larvae consume foliage, flowers or fruits, and/or rolls leaves together with silken threads, negatively affecting the growth and/or aesthetics of the crop. In order to understand the polyphagous behaviour of this species within an ornamental crop habitat, we hypothesized that different host plant species affect its life history traits differently. This study investigated the effects of the host plant species on larval and pupal durations and sizes, and fecundity (the number of eggs and the number and size of egg clutches). At 20°C, 60% RH and a 16L:8D photoperiod larvae developed 10, 14, 20 and 36 days faster when reared on Christmas berry, Photinia (Rosaceae), than on cherry laurel, Prunus laurocerasus (Rosaceae), New Zealand broadleaf, Griselinia littoralis (Griseliniaceae), Mexican orange, Choisya ternata (Rutaceae), and firethorn, Pyracantha angustifolia (Rosaceae), respectively. Female pupae were 23.8 mg heavier than male pupae, and pupal weight was significantly correlated with the duration of larval development. The lowest and the highest mean numbers of eggs were produced by females reared on Pyracantha (41) and Photinia (202), respectively. Clutch size differed significantly among moths reared on different host plants, although the total number of eggs did not differ. This study showed that different ornamental host plants affect the development of C. pronubana differently. Improved understanding of the influence of host plant on the moth's life history parameters measured here will help in determining the economic impact that this species may have within the ornamental plant production environment, and may be used in developing more accurate crop protection methodologies within integrated pest management of this insect.

Galleria mellonella as a screening tool to study virulence factors of Aspergillus fumigatus

The invertebrate Galleria mellonella has increasingly and widely been used in the last few years to study complex host–microbe interactions. Aspergillus fumigatus is one of the most pathogenic fungi causing life-threatening diseases in humans and animals. Galleria mellonella larvae has been proven as a reliable model for the analysis of pathogenesis and virulence factors, enable to screen a large number of A. fumigatus strains. This review describes the different uses of G. mellonella to study A. fumigatus and provides a comparison of the different protocols to trace fungal pathogenicity. The review also includes a summary of the diverse mutants tested in G. mellonella, and their respective contribution to A. fumigatus virulence. Previous investigations indicated that G. mellonella should be considered as an interesting tool even though a mammalian model may be required to complete and verify initial data.

The Larvicidal and Adulticidal Effects of Selected Plant Essential Oil Constituents on Greater Wax Moths

Some plant essential oil constituents, such as monoterpenoids and phenylpropanoids, are promising insecticides in some situations and for certain insect pests. They vary in their toxicity, depending on the target insect. Moths (Lepidoptera) appear susceptible to these compounds, making them of promise for use against greater wax moths (Galleria mellonella Fabricius, (Lepidoptera: Pyrallidae), GWM), an important pest of western honey bee (Apis mellifera Linnaeus. (Hymenoptera: Apidae)) colonies. We determined the LC50 for GWM larvae or LD50 for GWM adults of select compounds (thymol, carvacrol, (S)-(+)-carvone, estragole, citral, linalool, (S)-(-)-limonene, and γ-terpinene). Concentrations between 8 and 2,266 µg/cm3 were mixed into the diets of GWM larvae and doses ranging between 0.08 and 70.3 mg per adult were applied topically to the abdomens of GWM adults. Lethal concentrations and doses were calculated after of 72 h of exposure. All eight compounds showed insecticidal activity against all tested stages of GWMs. Thymol (LC50 µg/cm3 (95% CI) = 21 [9-56], carvacrol = 46 [26-79], citral = 63 [30-134], and carvone = 76 [33-201]) had the highest toxicity toward GWM larvae. The hydrocarbons limonene (296 [231-377]), estragole (466 [354-611]), and γ-terpinene (729 [630-857]) had the lowest toxicity toward GWM larvae. Thymol had the highest toxicity towards GWM adults (LD50 (CI) = 0.5 [0.4-0.8] mg/adult). However, carvacrol (11.6 [10.1-13.6]), linalool (12.9 [9.3-17.8]), and limonene (15.8 [13.1-19.2]) were less toxic to GWM larvae. Our data show that select plant essential oil constituents are promising controls of GWM.

Vertically Transmitted Gut Bacteria and Nutrition Influence the Immunity and Fitness of Bactrocera dorsalis Larvae

Symbiotic bacterial communities that colonize the digestive tract of tephritid fruit flies interact with nutrient intake to improve the flies' fitness and immunity. Some bacterial species consistently inhabit the tephritid guts and are transmitted to the next generation vertically. These species contribute significantly to some aspects of their host's physiology. In the current study, we examined the role of four vertically transmitted bacteria (Citrobacter, Enterobacter, Klebsiella, and Providencia) on the fitness parameters and immunity of Bactrocera dorsalis larvae that were fed a nutritionally manipulated diet. For this purpose, eggs were collected from axenic, gnotobiotic, and symbiotic adult flies, and larvae were reared on four types of diets in which carbohydrate and/or protein contents were reduced and then compared with larvae raised on a control diet. The diet and bacterial interactions significantly affected the fitness and immunity of B. dorsalis. Larvae of axenic flies grew slower and displayed weaker immune-based responses (PO activity, antibacterial activity, survival) than larvae of gnotobiotic and symbiotic flies. Overall, larvae reared on the low-protein diet grew slower than those reared on the control or low-carbohydrate diets. Survival, PO activity, and antibacterial activity were significantly lower in the hemolymph of larvae reared on low-protein diets. Our results also revealed that the levels of hemolymph protein, glucose, trehalose, and triglyceride in larvae from axenic flies were significantly lower than those in larvae of the symbiotic group after they fed on most of the tested diets. These results strongly infer that diet and vertically transmitted bacteria are both essential contributors to the fitness and immunity of B. dorsalis.

Overview of rearing and testing conditions and a guide for optimizing Galleria mellonella breeding and use in the laboratory for scientific purposes

The greater wax moth Galleria mellonella is an increasingly popular and consolidated alternative infection model to assess microbial virulence and the effectiveness of antimicrobial compounds. The lack of G. mellonella suppliers aiming at scientific purposes and a lack of well-established protocols for raising and testing these animals may impact results and reproducibility between different laboratories. In this review, we discuss the state of the art of rearing the larvae in situ, providing an overview of breeding and testing conditions commonly used and their influence on larval health and experiments results, from setting up the environment, providing the ideal diet, understanding the effects of pretreatments, choosing the best testing conditions, to exploring the most from the results obtained. Meanwhile, we guide the reader through the most practical ways of dealing with G. mellonella to achieve successful experiments.

Resource quality determines the evolution of resistance and its genetic basis

Parasites impose strong selection on their hosts, but the level of any evolved resistance may be constrained by the availability of resources. However, studies identifying the genomic basis of such resource-mediated selection are rare, particularly in nonmodel organisms. Here, we investigated the role of nutrition in the evolution of resistance to a DNA virus (PiGV), and any associated trade-offs in a lepidopteran pest species (Plodia interpunctella). Through selection experiments and whole-genome resequencing, we identify genetic markers of resistance that vary between the nutritional environments during selection. We do not find consistent evolution of resistance in the presence of virus but rather see substantial variation among replicate populations. Resistance in a low-nutrition environment is negatively correlated with growth rate, consistent with an established trade-off between immunity and development, but this relationship is highly context dependent. Whole-genome resequencing of the host shows that resistance mechanisms are likely to be highly polygenic and although the underlying genetic architecture may differ between high and low-nutrition environments, similar mechanisms are commonly used. As a whole, our results emphasize the importance of the resource environment on influencing the evolution of resistance.

Seasonal changes in immune response and reproductive investment in a biparental beetle

Immunity and reproduction are physiologically demanding processes, therefore trade-offs are expected between these life history traits. Furthermore, investments in these traits are also known to be affected by factors such as sex, body size, individual condition, seasonal changes and parasite infection. The relationship between immunity and reproduction and the effect of other factors on this relationship were investigated in many species, but there are a small number of studies on these patterns in biparental invertebrates. Lethrus apterus is an iteroparous biparental beetle with predominant female care in respect of collecting and processing food for larvae. Males guard the nest built underground and also their mate. Here we investigate how sex, body size, time within the reproductive season and parasite load may influence the relationship between immunocompetence and reproductive investment in this species. In beetles from a natural population we quantified immune response by measuring the encapsulation response, antimicrobial activity of hemolymph, the investment into reproductive tissues by measuring the size of testis follicles in males and total egg size in females, and parasite load by counting the number of mites on the beetles. We found that the encapsulation response is condition-dependent, as large individuals showed significantly higher encapsulation ability than small ones. Antimicrobial capacity was significantly higher in females than in males. In case of antimicrobial activity there was also a seasonal change in the relationship between immunity and reproductive investment, but only under heavy mite load. Reproductive investment was influenced by the interaction between body size and season (in females) and by body size and season (in males). Furthermore in females the interaction between antimicrobial activity and season indicated that reproductive investment increased with antimicrobial activity early in the reproductive season. By investigating the relationship between immunity and reproductive investment in a natural population of a biparental beetle species, we can conclude that investments into these important life history traits are governed by complex interactions between physiological and environmental factors. Our results are discussed in the context of life history evolution, highlighting the role of the assessed factors in shaping trade-offs themselves (in invertebrates).

Longer life span is associated with elevated immune activity in a seasonally polyphenic butterfly

Seasonal polyphenism constitutes a specific type of phenotypic plasticity in which short-lived organisms produce different phenotypes in different times of the year. Seasonal generations of such species frequently differ in their overall lifespan and in the values of traits closely related to fitness. Seasonal polyphenisms provide thus excellent, albeit underused model systems for studying trade-offs between life-history traits. Here, we compare immunological parameters between the two generations of the European map butterfly (Araschnia levana), a well-known example of a seasonally polyphenic species. To reveal possible costs of immune defence, we also examine the concurrent differences in several life-history traits. Both in laboratory experiments and in the field, last instar larvae heading towards the diapause (overwintering) had higher levels of both phenoloxidase (PO) activity and lytic activity than directly developing individuals. These results suggest that individuals from the diapausing generation with much longer juvenile (pupal) period invest more in their immune system than those from the short-living directly developing generation. The revealed negative correlation between pupal mass and PO activity may be one of the reasons why, in this species, the diapausing generation has a smaller body size than the directly developing generation. Immunological parameters may thus well mediate trade-offs between body size-related traits.

Ecological Stoichiometry: A Link Between Developmental Speed and Physiological Stress in an Omnivorous Insect

The elemental composition of organisms belongs to a suite of functional traits that may adaptively respond to fluctuating selection pressures. Life history theory predicts that predation risk and resource limitations impose selection pressures on organisms’ developmental time and are further associated with variability in energetic and behavioral traits. Individual differences in developmental speed, behaviors and physiology have been explained using the pace-of-life syndrome (POLS) hypothesis. However, how an organism’s developmental speed is linked with elemental body composition, metabolism and behavior is not well understood. We compared elemental body composition, latency to resume activity and resting metabolic rate (RMR) of western stutter-trilling crickets (Gryllus integer) in three selection lines that differ in developmental speed. We found that slowly developing crickets had significantly higher body carbon, lower body nitrogen and higher carbon-to-nitrogen ratio than rapidly developing crickets. Slowly developing crickets had significantly higher RMR than rapidly developing crickets. Male crickets had higher RMR than females. Slowly developing crickets resumed activity faster in an unfamiliar relative to a familiar environment. The rapidly developing crickets did the opposite. The results highlight the tight association between life history, physiology and behavior. This study indicates that traditional methods used in POLS research should be complemented by those used in ecological stoichiometry, resulting in a synthetic approach that potentially advances the whole field of behavioral and physiological ecology.

Applications of Invertebrate Animal Models to Dimorphic Fungal Infections

Dimorphic fungi can be found in the yeast form during infection and as hyphae in the environment and are responsible for a large number of infections worldwide. Invertebrate animals have been shown to be convenient models in the study of fungal infections. These models have the advantages of being low cost, have no ethical issues, and an ease of experimentation, time-efficiency, and the possibility of using a large number of animals per experiment compared to mammalian models. Invertebrate animal models such as Galleria mellonella, Caenorhabditis elegans, and Acanthamoebacastellanii have been used to study dimorphic fungal infections in the context of virulence, innate immune response, and the efficacy and toxicity of antifungal agents. In this review, we first summarize the features of these models. In this aspect, the growth temperature, genome sequence, availability of different strains, and body characteristics should be considered in the model choice. Finally, we discuss the contribution and advances of these models, with respect to dimorphic fungi Paracoccidioides spp., Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix spp., and Talaromyces marneffei (Penicillium marneffei).

From moths to caterpillars: Ideal conditions for Galleria mellonella rearing for in vivo microbiological studies

Galleria mellonella is a well-accepted insect model for the study of pathogen-host interactions and antimicrobial compounds. The main advantages of this model include the low cost of maintenance, the fast life cycle, the possibility of using a large number of caterpillars and the innate immune system, which is evolutionarily conserved relative to mammals. Because of these advantages, different research groups have been working to implement the rearing of G. mellonella in laboratory conditions. This protocol describes our experience in the rearing of G. mellonella caterpillars for experimental infection models and the influence of different artificial diets on developmental and physiological parameters. Here, we suggest a diet composition that benefits the life cycle of G. mellonella by accelerating the larval phase length and increasing the caterpillar weight. This diet also stimulated the immune system of G. mellonella by increasing the hemolymph volume and hemocyte concentration. In addition, our rearing protocol generated caterpillars that are more resistant to infection by Staphylococcus aureus, Escherichia coli and Candida albicans. A standard G. mellonella rearing protocol is fundamental to minimize external influences on the results, and this simple and easy protocol can support researchers starting to rear G. mellonella.

Cannibalism as a Possible Entry Route for Opportunistic Pathogenic Bacteria to Insect Hosts, Exemplified by Pseudomonas aeruginosa, a Pathogen of the Giant Mealworm Zophobas morio

Opportunistic bacteria are often ubiquitous and do not trigger disease in insects unless the conditions are specifically favorable for bacterial development in a suitable host. In this paper, we isolated and identified a bacterium, Pseudomonas aeruginosa, from the larvae of the giant mealworm Zophobas morio and we studied the possible entry routes by challenging larvae with per os injection and subdermal injection. We also evaluated the effect of exposing groups of larvae to P. aeruginosa inoculated in their feed and the effect of exposing wounded larvae to P. aeruginosa. We concluded that the mortality rate of Z. morio larvae is higher when P. aeruginosa gets in direct contact with the hemolymph via intracoelomic injection compared to a situation where the bacterium is force-fed. Larvae with an open wound exposed to P. aeruginosa presented higher mortality rate compared to larvae with a wound that was not exposed to the bacterium. We documented too, that cannibalism and scavenging were more prevalent among larvae in a group, when P. aeruginosa is present compared to when it is absent. We discuss hereby different aspects related with the pathogen’s entry routes to insects the complexity of pathogen´s transmission in high population densities and different ways to prevent and/or control P. aeruginosa in mass rearing systems.

Independent and interactive effects of immune activation and larval diet on adult immune function, growth and development in the greater wax moth (Galleria mellonella)

Organisms in the wild are likely to face multiple immune challenges as well as additional ecological stressors, yet their interactive effects on immune function are poorly understood. Insects are found to respond to cues of increased infection risk by enhancing their immune capacity. However, such adaptive plasticity in immune function may be limited by physiological and environmental constraints. Here, we investigated the effects of two environmental stressors - poor larval diet and an artificial parasite-like immune challenge at the pupal stage - on adult immune function, growth and development in the greater wax moth (Galleria mellonella). Males whose immune system was activated with an artificial parasite-like immune challenge had weaker immune response - measured as strength of encapsulation response - as adults compared to the control groups, but only when reared on high-nutrition larval diet. Immune activation did not negatively affect adult immune response in males reared on low-nutrition larval diet, indicating that poor larval diet improved the capacity of the insects to respond to repeated immune challenges. Low-nutrition larval diet also had a positive independent effect on immune capacity in females, yet it negatively affected development time and adult body mass in both sexes. As in the nature immune challenges are rarely isolated, and adverse nutritional environment may indicate an elevated risk of infection, resilience to repeated immune challenges as a response to poor nutritional conditions could provide a significant fitness advantage. This study highlights the importance of considering environmental context when investigating the effects of immune activation in insects.

Phenotypic variation in food utilization in an outbreak insect herbivore

The effects of nutrition may have subtantial impact on insect evolution by shaping different components of phenotypes. The key to undestanding this evolutionary process is to know how nutritional condition affects additive and nonadditive components of the phenotype. However, this is poorly understood in outbreaking insects. We investigated the additive and nonadditive variation present in food utilization traits in spruce budworm individuals subjected to chronic nutritional stress. A total of 160 full-sib families of spruce budworm (Choristoneura fumiferana Clem.) were raised under laboratory conditions, feeding on 2 diets (high and low energy) during 3 generations. Variables tested were pupal mass, consumption rate (RCR), growth rate (RGR), approximate digestibility (AD), the efficiency of conversion of digested food (ECD) and the efficiency of conversion of ingested food (ECI). Our results show that all traits tested presented a high percentage of nonadditive effects that modulate phenotype expression. We found a significant impact of family × diet interaction on pupal mass, RGR and ECD. Furthermore, these traits exhibited the greatest heritability. There was no evidence of presence of maternal effects. The results revealed that food utilization traits may evolve through epigenetics effects, such as phenotypic plasticity. This information can be used by modellers to improve forecast of spruce budworm population dynamics.

Social immunity in honeybees-Density dependence, diet, and body mass trade-offs

Group living is favorable to pathogen spread due to the increased risk of disease transmission among individuals. Similar to individual immune defenses, social immunity, that is antiparasite defenses mounted for the benefit of individuals other than the actor, is predicted to be altered in social groups. The eusocial honey bee (Apis mellifera) secretes glucose oxidase (GOX), an antiseptic enzyme, throughout its colony, thereby providing immune protection to other individuals in the hive. We conducted a laboratory experiment to investigate the effects of group density on social immunity, specifically GOX activity, body mass and feeding behavior in caged honey bees. Individual honeybees caged in a low group density displayed increased GOX activity relative to those kept at a high group density. In addition, we provided evidence for a trade-off between GOX activity and body mass: Individuals caged in the low group density had a lower body mass, despite consuming more food overall. Our results provide the first experimental evidence that group density affects a social immune response in a eusocial insect. Moreover, we showed that the previously reported trade-off between immunity and body mass extends to social immunity. GOX production appears to be costly for individuals, and potentially the colony, given that low body mass is correlated with small foraging ranges in bees. At high group densities, individuals can invest less in social immunity than at low densities, while presumably gaining shared protection from infection. Thus, there is evidence that trade-offs at the individual level (GOX vs. body mass) can affect colony-level fitness.

Novel approach to study gastropod-mediated innate immune reactions against metastrongyloid parasites

The anthropozoonotic metastrongyloid nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis, as well as Angiostrongylus vasorum, Crenosoma vulpis, Aelurostrongylus abstrusus and Troglostrongylus brevior are currently considered as emerging gastropod-borne parasites and have gained growing scientific attention in the last years. However, the knowledge on invertebrate immune responses and on how metastrongyloid larvae are attacked by gastropod immune cells is still limited. This work aims to describe an in vitro system to investigate haemocyte-derived innate immune responses of terrestrial gastropods induced by vital axenic metastrongyloid larvae. We also provide protocols on slug/snail management and breeding under standardized climate conditions (circadian cycle, temperature and humidity) for the generation of parasite-free F0 stages which are essential for immune-related investigations. Adult slug species (Arion lusitanicus, Limax maximus) and giant snails (Achatina fulica) were maintained in fully automated climate chambers until mating and production of fertilized eggs. Newly hatched F0 juvenile specimens were kept under parasite-free conditions before experimental use. An improved protocol for gastropod haemolymph collection and haemocyte isolation was established. Giemsa-stained haemolymph preparations showed adequate haemocyte isolation in all three gastropod species. Additionally, a protocol for the production of axenic first and third stage larvae (L1, L3) was established. Haemocyte functionality was tested in haemocyte-nematode-co-cultures. Scanning electron microscopy (SEM) and light microscopy analyses revealed that gastropod-derived haemocytes formed clusters as well as DNA-rich extracellular aggregates catching larvae and decreasing their motility. These data confirm the usefulness of the presented methods to study haemocyte-mediated gastropod immune responses to better understand the complex biology of gastropod-borne diseases.

Microbiome symbionts and diet diversity incur costs on the immune system of insect larvae

Communities of symbiotic microorganisms that colonize the gastrointestinal tract play an important role in food digestion and protection against opportunistic microbes. Diet diversity increases the number of symbionts in the intestines, a benefit that is considered to impose no cost for the host organism. However, less is known about the possible immunological investments that hosts have to make in order to control the infections caused by symbiont populations that increase because of diet diversity. Using taxonomical composition analysis of the 16S rRNA V3 region, we show that enterococci are the dominating group of bacteria in the midgut of the larvae of the greater wax moth (Galleria mellonella). We found that the number of colony-forming units of enterococci and expressions of certain immunity-related antimicrobial peptide (AMP) genes such as Gallerimycin, Gloverin, 6-tox, Cecropin-D and Galiomicin increased in response to a more diverse diet, which in turn decreased the encapsulation response of the larvae. Treatment with antibiotics significantly lowered the expression of all AMP genes. Diet and antibiotic treatment interaction did not affect the expression of Gloverin and Galiomicin AMP genes, but significantly influenced the expression of Gallerimycin, 6-tox and Cecropin-D Taken together, our results suggest that diet diversity influences microbiome diversity and AMP gene expression, ultimately affecting an organism's capacity to mount an immune response. Elevated basal levels of immunity-related genes (Gloverin and Galiomicin) might act as a prophylactic against opportunistic infections and as a mechanism that controls the gut symbionts. This would indicate that a diverse diet imposes higher immunity costs on organisms.

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.

The Biology and Control of the Greater Wax Moth, Galleria mellonella

The greater wax moth, Galleria mellonella Linnaeus, is a ubiquitous pest of the honeybee, Apis mellifera Linnaeus, and Apis cerana Fabricius. The greater wax moth larvae burrow into the edge of unsealed cells with pollen, bee brood, and honey through to the midrib of honeybee comb. Burrowing larvae leave behind masses of webs which causes galleriasis and later absconding of colonies. The damage caused by G. mellonella larvae is severe in tropical and sub-tropical regions, and is believed to be one of the contributing factors to the decline in both feral and wild honeybee populations. Previously, the pest was considered a nuisance in honeybee colonies, therefore, most studies have focused on the pest as a model for in vivo studies of toxicology and pathogenicity. It is currently widespread, especially in Africa, and the potential of transmitting honeybee viruses has raised legitimate concern, thus, there is need for more studies to find sustainable integrated management strategies. However, our knowledge of this pest is limited. This review provides an overview of the current knowledge on the biology, distribution, economic damage, and management options. In addition, we provide prospects that need consideration for better understanding and management of the pest.

Impact of cold on the immune system of burying beetle, Nicrophorus vespilloides (Coleoptera: Silphidae)

Insect overwintering is one of the most astonishing phases of the insect life cycle. Despite vast amounts of knowledge available about the physiological mechanisms of this phenomenon, the impact of stress factors on insect immune system functioning during the winter is still unknown. The aim of this study is to analyze how low temperatures influence the immune system of the beetle Nicrophorus vespilloides. The results show that the beetle's immune system is differently modulated by cold induced in laboratory settings than that which occurs in natural conditions. Among beetles cultured in conditions similar to summer, low temperatures, did not influence the number of circulating haemocytes, phenoloxidase activity, haemocytes morphology, and percentage ratio of haemocyte types. In these beetles, differences were noted only in the ability of haemocytes to perform phagocytosis. Individuals acclimated in natural conditions in autumn had a higher level of humoral response and a different percentage ratio of haemocyte types. During the winter period, the number of haemocytes in the beetles decreased, but the percentage ratio of phagocytic haemocytes increased. Furthermore, we noted an increase of phenoloxidase activity. Our study also showed mitotic divisions of haemocytes in haemolymph collected from burying beetles after cold exposure and from burying beetles collected from natural conditions during autumn and winter. Differences in response to low temperatures in laboratory conditions and the natural environment suggest that the simultaneous presence of other stress factors during winter such as desiccation and starvation have a significant influence on the activity of burying beetle's immune system.

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.

Nutritional and non-nutritional food components modulate phenotypic variation but not physiological trade-offs in an insect

Our understanding of how food modulates animal phenotypes and mediate trade-offs between life-history traits has benefited greatly from the study of combinations of nutritional and non-nutritional food components, such as plant secondary metabolites. We used a fruit fly pest, Anastrepha ludens, to examine phenotypic variation across larval, pupal and adult stages as a function of larval food with varying nutrient balance and content of chlorogenic acid, a secondary metabolite. Larval insects that fed on carbohydrate-biased diets relative to protein exhibited longer larval and pupal developmental periods, were often heavier as pupae and resisted desiccation and starvation for longer periods in the adult stage than insects fed on highly protein-biased diets. Except for a potential conflict between pupal development time and adult desiccation and starvation resistance, we did not detect physiological trade-offs mediated by the nutritional balance in larval food. Chlorogenic acid affected A. ludens development in a concentration and nutrient-dependent manner. Nutrients and host plant secondary metabolites in the larval diet induced changes in A. ludens phenotype and could influence fruit fly ecological interactions. We provide a unique experimental and modelling approach useful in generating predictive models of life history traits in a variety of organisms.

A dark cuticle allows higher investment in immunity, longevity and fecundity in a beetle upon a simulated parasite attack

Cuticle melanism in insects is linked to a number of life history traits: a positive relationship is hypothesized between melanism, immune function, fecundity and lifespan. However, it is not clear how activation of the immune system affects trade-offs between life history traits in female mealworm beetles (Tenebrio molitor) differing in cuticle melanization. The females with tan, brown and black cuticles examined in the present study did not differ in the intensity of encapsulation response, fecundity and longevity when their immune system was not activated. However, we found that immune activation and cuticle melanization have a significant effect on life history traits. Offspring number and lifespan decreased in females with tan and brown cuticles, while the fecundity and lifespan of black females were not affected. Importantly, we inserted the implants again and found a significant decrease in the strength of encapsulation response in females with tan and brown cuticles. In contrast, black females increased melanotic reactions against the nylon implant, suggesting immunological priming. The results show that cuticle melanization plays an important adaptive role under the risk of being infected, while the lack of these benefits before the insertion of nylon monofilaments suggests that there are costs associated with an activated immunity system.

Reconfiguration of the immune system network during food limitation in the caterpillar Manduca sexta

Dwindling resources might be expected to induce a gradual decline in immune function. However, food limitation has complex and seemingly paradoxical effects on the immune system. Examining these changes from an immune system network perspective may help illuminate the purpose of these fluctuations. We found that food limitation lowered long-term (i.e. lipid) and short-term (i.e. sugars) energy stores in the caterpillar Manduca sexta. Food limitation also: altered immune gene expression, changed the activity of key immune enzymes, depressed the concentration of a major antioxidant (glutathione), reduced resistance to oxidative stress, reduced resistance to bacteria (Gram-positive and -negative bacteria) but appeared to have less effect on resistance to a fungus. These results provide evidence that food limitation led to a restructuring of the immune system network. In severely food-limited caterpillars, some immune functions were enhanced. As resources dwindled within the caterpillar, the immune response shifted its emphasis away from inducible immune defenses (i.e. those responses that are activated during an immune challenge) and increased emphasis on constitutive defenses (i.e. immune components that are produced consistently). We also found changes suggesting that the activation threshold for some immune responses (e.g. phenoloxidase) was lowered. Changes in the configuration of the immune system network will lead to different immunological strengths and vulnerabilities for the organism.

Effects of immune challenge on the oviposition strategy of a noctuid moth

Infections can have detrimental effects on the fitness of an animal. Reproducing females may therefore be sensitive to cues of infection and be able to adaptively change their oviposition strategy in the face of infection. As one possibility, females could make a terminal investment and shift reproductive effort from future to current reproduction as life expectancy decreases. We hypothesized that females of the noctuid moth Heliothis virescens make a terminal investment and adapt their oviposition timing as well as their oviposition site selectivity in response to an immune challenge. We indeed found that females that were challenged with the bacterial entomopathogen Serratia entomophila laid more eggs than control females one night after the challenge. Additionally, bacteria-challenged females were less discriminating between oviposition sites than control females. Whereas control females preferred undamaged over damaged plants, immune-challenged females did not differentiate between the two. These results indicate that terminal investment is part of the life history of H. virescens females. Moreover, our results suggest that the strategy of terminal investment in H. virescens oviposition represents a fitness trade-off for females: in the face of infection, an increase in oviposition rate enhances female fitness, whereas low oviposition site selectivity reduces female fitness.