Recent advances in the integrative nutrition of arthropods

Increased intake of tree forage by moose is associated with intake of crops rich in nonstructural carbohydrates

Animals representing a wide range of taxonomic groups are known to select specific food combinations to achieve a nutritionally balanced diet. The nutrient balancing hypothesis suggests that, when given the opportunity, animals select foods to achieve a particular target nutrient balance, and that balancing occurs between meals and between days. For wild ruminants who inhabit landscapes dominated by human land use, nutritionally imbalanced diets can result from ingesting agricultural crops rich in starch and sugar (nonstructural carbohydrates [NCs]), which can be provided to them by people as supplementary feeds. Here, we test the nutrient balancing hypothesis by assessing potential effects that the ingestion of such crops by Alces alces (moose) may have on forage intake. We predicted that moose compensate for an imbalanced intake of excess NC by selecting tree forage with macro-nutritional content better suited for their rumen microbiome during wintertime. We applied DNA metabarcoding to identify plants in fecal and rumen content from the same moose during winter in Sweden. We found that the concentration of NC-rich crops in feces predicted the presence of Picea abies (Norway spruce) in rumen samples. The finding is consistent with the prediction that moose use tree forage as a nutritionally complementary resource to balance their intake of NC-rich foods, and that they ingested P. abies in particular (normally a forage rarely eaten by moose) because it was the most readily available tree. Our finding sheds new light on the foraging behavior of a model species in herbivore ecology, and on how habitat alterations by humans may change the behavior of wildlife.

Adult Feeding Experience Determines the Fecundity and Preference of the Henosepilachna vigintioctopunctata (F.) (Coleoptera: Coccinellidae)

Both larvae and adults of the Henosepilachna vigintioctopunctata feed on leaves of potatoes, tomatoes, and eggplants. Given the variation in planting times of host plants in the Jianghan Plain, host switching between larvae and adults of H. vigintioctopunctata is inevitable to ensure continuous food availability. We evaluated the effect of consistent versus diverse larval and adult host plant feeding experience on growth performance, fecundity, longevity, and feeding preferences of H. vigintioctopunctata through match-mismatch experiments. Host plant quality significantly influences larval development and adult reproduction. Potatoes are identified as the optimal host plant for H. vigintioctopunctata, whereas eggplants significantly negatively affect the adult fecundity. Adult stage host feeding experience determines the fecundity of H. vigintioctopunctata, irrespective of the larval feeding experience. The fecundity of H. vigintioctopunctata adults on eggplant leaves remains significantly lower than that observed on potato leaves. Similarly, adult H. vigintioctopunctata demonstrate a preference for consuming potato leaves, irrespective of the larval feeding experience. Although host switching between larval and adult stages offers lesser benefits for the performance of herbivorous insects compared to a consistent diet with potato leaves, it maintains H. vigintioctopunctata population continuity amidst shortages of high-quality potato hosts.

Viral Infection Induces Changes to the Metabolome, Immune Response and Development of a Generalist Insect Herbivore

Host plant consumption and pathogen infection commonly influence insect traits related to development and immunity, which are ultimately reflected in the behavior and physiology of the insect. Herein, we explored changes in the metabolome of a generalist insect herbivore, Vanessa cardui (Lepidoptera: Nymphalidae), in response to both dietary variation and pathogen infection in order to gain insight into tritrophic interactions for insect metabolism and immunity. Caterpillars were reared on two different host plants, Plantago lanceolata (Plantaginaceae) and Taraxacum officinale (Asteraceae) and subjected to a viral infection by Junonia coenia densovirus (JcDV), along with assays to determine the insect immune response and development. Richness and diversity of plant and caterpillar metabolites were evaluated using a liquid chromatography-mass spectrometry approach and showed that viral infection induced changes to the chemical content of V. cardui hemolymph and frass dependent upon host plant consumption. Overall, the immune response as measured by phenoloxidase (PO) enzymatic activity was higher in individuals feeding on P. lanceolata compared with those feeding on T. officinale. Additionally, infection with JcDV caused suppression of PO activity, which was not host plant dependent. We conclude that viral infection combined with host plant consumption creates a unique chemical environment, particularly within the insect hemolymph. Whether and how these metabolites contribute to defense against viral infection is an open question in chemical ecology.

Alanine metabolism mediates energy allocation of the brown planthopper to adapt to resistant rice

INTRODUCTION

During the adaptation to host plant resistance, herbivorous insects faced the challenge of overcoming plant defenses while ensuring their own development and reproductive success. To achieve this, a strategic allocation of energy resources for detoxification and ecological fitness maintenance became essential.

OBJECTIVE

This study aimed to elucidate the intricate energy allocation mechanisms involved in herbivore adaptation that are currently poorly understood.

METHODS

The rice Oryza sativa and its monophagous pest, the brown planthopper (BPH), Nilaparvata lugens were used as a model system. An integrated analysis of metabolomes and transcriptomes from different BPH populations were conducted to identify the biomarkers. RNA interference of key genes and exogenous injection of key metabolites were performed to validate the function of biomarkers.

RESULTS

We found that alanine was one of the key biomarkers of BPH adaptation to resistant rice variety IR36. We also found that alanine flow determined the adaptation of BPH to IR36 rice. The alanine aminotransferase (ALT)-mediated alanine transfer to pyruvate was necessary and sufficient for the adaptation. This pathway may be conserved, at least to some extent, in BPH adaptation to multiple rice cultivars with different resistance genes. More importantly, ALT-mediated alanine metabolism is the foundation of downstream energy resource allocation for the adaptation. The adapted BPH population exhibited a significantly higher level of energy reserves in the fat body and ovary when fed with IR36 rice, compared to the unadapted population. This rendered the elevated detoxification in the adapted BPH and their ecological fitness recovery.

CONCLUSION

Overall, our findings demonstrated the crucial role of ALT-mediated alanine metabolism in energy allocation during the adaptation to resistant rice in BPH. This will provide novel knowledge regarding the co-evolutionary mechanisms between herbivores and their host plants.

Fitness of Nutrition Regulation in a Caterpillar Pest Mythimna separata (Walker): Insights from the Geometric Framework

In nature, plants can contain variable nutrients depending upon the species, tissue, and developmental stage. Insect herbivores may regulate their nutrient intake behaviorally and physio- logically when encountering different foods. This study examined the nutritional regulation of the oriental armyworm, Mythimna separata, for the first time. In one experiment, we allowed the cater-pillars to choose between two nutritionally balanced but complementary diets. The caterpillars did not randomly consume the paired foods, but instead chose between the nutritionally balanced but complementary diets. This intake behavior was found to change with their developmental stages. Furthermore, the nutrient concentrations in food significantly impacted the insect's performance. In the other experiment, caterpillars were given one of eleven diets that reflected the different nutrient conditions in the field. The results showed that proteins were significantly associated with developmental time and fecundity. For example, by consuming protein-biased food, the caterpillars developed faster and produced more eggs. In contrast, carbohydrates were more strongly linked to lipid accumulation, and caterpillars accumulated more lipids when consuming the carbohydrate-biased food. Moreover, the caterpillars were also found to actively regulate their intake of proteins and carbohydrates based on food quality and to physiologically prepare for subsequent life stages. These findings enhance our understanding of how M. separata feeds and responds to different nutritional environments in the field, which could have implications for managing insect herbivores in agricultural settings.

Towards an integrated understanding of dietary phenotypes

Diet and nutrition comprise a complex, multi-faceted interface between animal biology and food environments. With accumulating information on the many facets of this association arises a need for systems-based approaches that integrate dietary components and their links with ecology, feeding, post-ingestive processes and the functional and ecological consequences of these interactions. We briefly show how a modelling approach, nutritional geometry, has used the experimental control afforded in laboratory studies to begin to unravel these links. Laboratory studies, however, have limited ability to establish whether and how the feeding and physiological mechanisms interface with realistic ecological environments. We next provide an overview of observational field studies of free-ranging primates that have examined this, producing largely correlative data suggesting that similar feeding mechanisms operate in the wild as in the laboratory. Significant challenges remain, however, in establishing causal links between feeding, resource variation and physiological processes in the wild. We end with a more detailed account of two studies of temperate primates that have capitalized on the discrete variation provided by seasonal environments to strengthen causal inference in field studies and link patterns of intake to dynamics of nutrient processing. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Relationships among Development, Growth, Body Size, Reproduction, Aging, and Longevity - Trade-Offs and Pace-Of-Life

Relationships of growth, metabolism, reproduction, and body size to the biological process of aging and longevity have been studied for decades and various unifying "theories of aging" have been proposed to account for the observed associations. In general, fast development, early sexual maturation leading to early reproductive effort, as well as production of many offspring, have been linked to shorter lifespans. The relationship of adult body size to longevity includes a remarkable contrast between the positive correlation in comparisons between different species and the negative correlation seen in comparisons of individuals within the same species. We now propose that longevity and presumably also the rate of aging are related to the "pace-of-life." A slow pace-of-life including slow growth, late sexual maturation, and a small number of offspring, predicts slow aging and long life. The fast pace of life (rapid growth, early sexual maturation, and major reproductive effort) is associated with faster aging and shorter life, presumably due to underlying trade-offs. The proposed relationships between the pace-of-life and longevity apply to both inter- and intra-species comparisons as well as to dietary, genetic, and pharmacological interventions that extend life and to evidence for early life programming of the trajectory of aging. Although available evidence suggests the causality of at least some of these associations, much further work will be needed to verify this interpretation and to identify mechanisms that are responsible.

Insect Microbial Symbionts: Ecology, Interactions, and Biological Significance

The guts of insect pests are typical habitats for microbial colonization and the presence of bacterial species inside the gut confers several potential advantages to the insects. These gut bacteria are located symbiotically inside the digestive tracts of insects and help in food digestion, phytotoxin breakdown, and pesticide detoxification. Different shapes and chemical assets of insect gastrointestinal tracts have a significant impact on the structure and makeup of the microbial population. The number of microbial communities inside the gastrointestinal system differs owing to the varying shape and chemical composition of digestive tracts. Due to their short generation times and rapid evolutionary rates, insect gut bacteria can develop numerous metabolic pathways and can adapt to diverse ecological niches. In addition, despite hindering insecticide management programs, they still have several biotechnological uses, including industrial, clinical, and environmental uses. This review discusses the prevalent bacterial species associated with insect guts, their mode of symbiotic interaction, their role in insecticide resistance, and various other biological significance, along with knowledge gaps and future perspectives. The practical consequences of the gut microbiome and its interaction with the insect host may lead to encountering the mechanisms behind the evolution of pesticide resistance in insects.

Nutrigonometry IV: Thales' theorem to measure the rules of dietary compromise in animals

Diet specialists and generalists face a common challenge: they must regulate the intake and balance of nutrients to achieve a target diet for optimum nutrition. When optimum nutrition is unattainable, organisms must cope with dietary imbalances and trade-off surplus and deficits of nutrients that ensue. Animals achieve this through compensatory rules that dictate how to cope with nutrient imbalances, known as 'rules of compromise'. Understanding the patterns of the rules of compromise can provide invaluable insights into animal physiology and behaviour, and shed light into the evolution of diet specialisation. However, we lack an analytical method for quantitative comparisons of the rules of compromise within and between species. Here, I present a new analytical method that uses Thales' theorem as foundation, and that enables fast comparisons of the rules of compromise within and between species. I then apply the method on three landmark datasets to show how the method enables us to gain insights into how animals with different diet specialisation cope with nutrient imbalances. The method opens new avenues of research to understand how animals cope with nutrient imbalances in comparative nutrition.

Effects of Host Plants on Development and Immunity of a Generalist Insect Herbivore

Secondary plant chemistry mediates a variety of communication signals among species, playing a fundamental role in the evolutionary diversification of communities and ecosystems. Herein, we explored diet-mediated host plant effects on development and immune response of a generalist insect herbivore. Vanessa cardui (Nymphalidae) caterpillars were reared on leaves of three host plants that vary in secondary metabolites, Plantago lanceolata (Plantaginaceae), Taraxacum officinale (Asteraceae) and Tithonia diversifolia (Asteraceae). Insect development was evaluated by larval and pupal viabilities, survivorship, and development rate. Immune response was measured as phenoloxidase (PO) activity. Additionally, chemical profiles of the host plants were obtained by liquid chromatograph-mass spectrometry (LC-MS) and the discriminant metabolites were determined using a metabolomic approach. Caterpillars reared on P. lanceolata exhibited the highest larval and pupal viabilities, as well as PO activity, and P. lanceolata leaves were chemically characterized by the presence of iridoid glycosides, phenylpropanoids and flavonoids. Taraxacum officinale leaves were characterized mainly by the presence of phenylpropanoids, flavones O-glycoside and germacranolide-type sesquiterpene lactones; caterpillars reared on this host plant fully developed to the adult stage, however they exhibited lower larval and pupal viabilities compared to individuals reared on P. lanceolata. Conversely, caterpillars reared on T. diversifolia leaves, which contain phenylpropanoids, flavones and diverse furanoheliangolide-type sesquiterpene lactones, were not able to complete larval development and exhibited the lowest PO activity. These findings suggested that V. cardui have adapted to tolerate potentially toxic metabolites occurring in P. lanceolata (iridoid glycosides), however caterpillars were not able to cope with potentially detrimental metabolites occurring in T. diversifolia (furanoheliangolides). Therefore, we suggest that furanoheliangolide-type sesquiterpene lactones were responsible for the poor development and immune response observed for caterpillars reared on T. diversifolia.

Development of Spodoptera exigua Population: Does the Nutritional Status Matter?

Spodoptera exigua (Hübner) is a common agricultural pest that can harm hundreds of crops. Nutrition conditions can significantly affect the development of insects, especially carbohydrates (C) and proteins (P), which are the two most critical nutrients. To study the development of the S. exigua population under different carbohydrate and protein nutrition conditions, we constructed a life table of both sexes of an S. exigua population under three artificial diets: high nitrogen (P:C = 7:1), medium nitrogen, medium sugar (P:C = 1:1), and high sugar (P:C = 1:7). The results showed that the generation time of S. exigua was 26.38 ± 0.54 d under the medium nitrogen-medium sugar diet, which was the shortest among the three nutrition conditions. The intrinsic rate of increase (0.18 ± 0.01), finite rate of increase (1.20 ± 0.01), fecundity (605.42 ± 36.33 eggs/female), and predicted population at 100 days (8,840,000) were significantly higher under the medium nitrogen-medium sugar condition. There was no significant difference in the net reproductive rate among the three conditions. These results suggested that an appropriate protein:carbohydrate ratio is beneficial to the rapid development of S. exigua on farmland. These findings are important for scientifically predicting the population dynamics of S. exigua from the perspective of nutritional ecology, understanding its catastrophic mechanism, and constructing a prevention and control system.

The Feeding Behaviour of Gall Midge Larvae and Its Implications for Biocontrol of the Giant Reed: Insights from Stable Isotope Analysis

The gall midge Lasioptera donacis, whose larval stage interferes with the reed's leaf development, is a potential candidate agent for the biological control of Arundo donax. Reed infestation is always associated with the presence of a saprophytic fungus, Arthrinium arundinis, which is believed to provide food for the larvae. Larvae also interact with a parasitic nematode, Tripius gyraloura, which can be considered its natural enemy. To deepen our knowledge of the plant-fungus-insect trophic interactions and to understand the effects of the nematode on midge larval feeding behaviour, we applied stable isotope analysis, one of the most effective methods for investigating animal feeding preferences in various contexts. The results showed that on average the fungus accounted for 65% of the diet of the midge larvae, which however consumed the reed and the fungus in variable proportions depending on reed quality (expressed as the C:N ratio). No differences in feeding behaviour were observed between parasitised and non-parasitised midge larvae, indicating that nematodes have no effect in this regard. Due to its trophic habits, L. donacis could be an effective control agent of A. donax and these results need to be considered when implementing biological control measures.

Effect of non-essential amino acids (proline and glutamic acid) and sugar polyol (sorbitol) on brood of honey bees

Dietary nutrients provide fuel for the growth and development of insects as well as chemicals for their tissue construction. Apis mellifera L., an important pollinator, collects nectar and pollens from different plants to get their nutritional needs. Honey bees use protein for growth and development and carbohydrates as energy sources. Pollens predominantly contain proline and glutamic acid (non-essential amino acids). This is the first study to evaluate the role of proline, glutamic acid and sorbitol on bee broods. The composition of the diet can optimize the in vitro rearing process. Therefore, we elaborated on the possible impact of these amino acids and sugar alcohol on bee broods. This study aimed to achieve this objective by rearing honey bee larvae under different concentrations of proline, glutamic acid, and sorbitol (1, 4 and 8%), which were supplemented into the standard larval diet. The supplementation of proline helped the quick development of larvae and pupae of honey bees, whereas developmental time only decreased in pupae in the case of glutamic acid. The duration of the total bee brood development was the shortest (20.1 and 20.6 days) on Pro8 and Glu4, respectively. Proline only increased larvae survival (93.8%), whereas glutamic acid did not increase the survival of any brood stage. Pupal and adult weights were also increased with proline and glutamic acid-supplemented diets. Sorbitol did not change the developmental period of the honey bee brood but increased larval survival (93.7%) only at the lowest concentration (Sor1). The small concentration of sorbitol can be used to increase the survival of the honey bee brood. However, a higher concentration (Sor8) of sorbitol reduced the body weight of both pupae and adults. This study predicted that rearing bee brood could be one of the factors for the selectivity of pollen with higher proline and glutamic acid during the foraging of bees.

Understanding nutritive need in Harmonia axyridis larvae: Insights from nutritional geometry

The multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an important natural enemy in agricultural ecosystems. In spite of being a carnivore consuming protein-rich preys, the lady beetles often consume carbohydrate-rich food like nectar or honeydew. However, most studies on nutrition regulation of carnivores mainly focus on protein and lipid, two major macronutrients in preys. In this study, nutrition regulation of protein and carbohydrate has been investigated in the 4th instar larvae of H. axyridis using Geometric Framework. We provided the insects two pairs of foods, one a protein-biased one and the second carbohydrate-biased, to determine the intake target. We then confined them to nutritionally imbalanced foods to examine how they regulated food intake to achieve maximal performance. The larvae performed well on the 2 foods that containing the closest P : C ratios to the intake target, but, surprisingly, the lipid content was much lower than that in the choice experiment. The lady beetles seemed to maintain the optimal lipid content by consuming carbohydrate-rich food. Moreover, consuming the carbohydrate-rich food was less metabolically expensive than the protein-rich food. Therefore, switching behavior between plant and animal foods actually reflects their nutritive needs. These findings extended our understanding of predator forage behavior and its influence on food web in ecosystems, and shed light on the role of agri-environment schemes in meeting the nutritional need of predators in field.

Development of a polyphagous leaf beetle on different host plant species and its detoxification of glucosinolates

Herbivores face a broad range of defences when feeding on plants. By mixing diets, polyphagous herbivores are assumed to benefit during their development by gaining a better nutritional balance and reducing the intake of toxic compounds from individual plant species. Nevertheless, they also show strategies to metabolically cope with plant defences. In this study, we investigated the development of the polyphagous tansy leaf beetle, Galeruca tanaceti (Coleoptera: Chrysomelidae), on mono diets consisting of one plant species [cabbage (Brassica rapa), Brassicaceae; lettuce (Lactuca sativa), or tansy (Tanacetum vulgare), Asteraceae] vs. two mixed diets, both containing tansy. Leaves of the three species were analysed for contents of water, carbon and nitrogen, the specific leaf area (SLA) and trichome density. Furthermore, we studied the insect metabolism of two glucosinolates, characteristic defences of Brassicaceae. Individuals reared on cabbage mono diet developed fastest and showed the highest survival, while the development was slowest for individuals kept on tansy mono diet. Cabbage had the lowest water content, while tansy had the highest water content, C/N ratio and trichome density and the lowest SLA. Lettuce showed the lowest C/N ratio, highest SLA and no trichomes. Analysis of insect samples with UHPLC-DAD-QTOF-MS/MS revealed that benzyl glucosinolate was metabolised to N-benzoylglycine, N-benzoylalanine and N-benzoylserine. MALDI-Orbitrap-MS imaging revealed the localisation of these metabolites in the larval hindgut region. 4-Hydroxybenzyl glucosinolate was metabolised to N-(4-hydroxybenzoyl)glycine. Our results highlight that G. tanaceti deals with toxic hydrolysis products of glucosinolates by conjugation with different amino acids, which may enable this species to develop well on cabbage. The high trichome density and/or specific plant chemistry may lower the accessibility and/or digestibility of tansy leaves, leading to a poorer beetle development on pure tansy diet or diet mixes containing tansy. Thus, diet mixing is not necessarily beneficial, if one of the plant species is strongly defended.

The role of genetically engineered soybean and Amaranthus weeds on biological and reproductive parameters of Spodoptera cosmioides (Lepidoptera: Noctuidae)

BACKGROUND

In soybean fields containing insecticide- and herbicide-resistant genetically engineered varieties, some weed species have increasingly become difficult to manage and may favor the population growth of secondary pests like Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae). To test this hypothesis, we measured life-history traits, population growth parameters and adult nutrient content of S. cosmioides reared on foliage from four Amaranthus species, from Cry1Ac Bt and non-Bt soybean varieties, and on meridic artificial diet.

RESULTS

Larvae reared on A. palmeri and A. spinosus had a shorter development time (5-7 days) than larvae raised on the soybean varieties and A. hybridus. Armyworm survival probability was zero on A. viridis and highest (80% and 71%) on soybeans and A. palmeri. The latter and the artificial diet produced the heaviest larvae and pupae, in contrast to the non-Bt soybean variety. Body nutrient content diverged mostly for adults reared on artificial diet compared with those raised on the soybean varieties. The intrinsic rate of population increase (overall fitness) was 27.88% higher for the armyworms on A. palmeri, Cry1Ac Bt soybean and artificial diet compared with those on non-Bt soybean, A. spinosus and A. hybridus.

CONCLUSIONS

Cry1Ac soybean fields infested by some Amaranthus weeds, especially A. palmeri, are conducive to the population growth of S. cosmioides. Integrated pest management programs may be needed to properly manage S. cosmioides in soybean fields, with surveillance for population peaks and judicious control measures when needed. © 2022 Society of Chemical Industry.

Eating in a losing cause: limited benefit of modified macronutrient consumption following infection in the oriental cockroach Blatta orientalis

BACKGROUND

Host-pathogen interactions can lead to dramatic changes in host feeding behaviour. One aspect of this includes self-medication, where infected individuals consume substances such as toxins or alter their macronutrient consumption to enhance immune competence. Another widely adopted animal response to infection is illness-induced anorexia, which is thought to assist host immunity directly or by limiting the nutritional resources available to pathogens. Here, we recorded macronutrient preferences of the global pest cockroach, Blatta orientalis to investigate how shifts in host macronutrient dietary preference and quantity of carbohydrate (C) and protein (P) interact with immunity following bacterial infection.

RESULTS

We find that B. orientalis avoids diets enriched for P under normal conditions, and that high P diets reduce cockroach survival in the long term. However, following bacterial challenge, cockroaches significantly reduced their overall nutrient intake, particularly of carbohydrates, and increased the relative ratio of protein (P:C) consumed. Surprisingly, these behavioural shifts had a limited effect on cockroach immunity and survival, with minor changes to immune protein abundance and antimicrobial activity between individuals placed on different diets, regardless of infection status.

CONCLUSIONS

We show that cockroach feeding behaviour can be modulated by a pathogen, resulting in an illness-induced anorexia-like feeding response and a shift from a C-enriched to a more P:C equal diet. However, our results also indicate that such responses do not provide significant immune protection in B. orientalis, suggesting that the host's dietary shift might also result from random rather than directed behaviour. The lack of an apparent benefit of the shift in feeding behaviour highlights a possible reduced importance of diet in immune regulation in these invasive animals, although further investigations employing pathogens with alternative infection strategies are warranted.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

Balancing nutrients in a toxic environment: the challenge of eating

Insect herbivores can regulate their food intake by mixing food sources with different nutrient content, but face the resulting challenge of ingesting various plant secondary metabolites. How insects deal with toxins in a complex nutrient environment is unclear. Here we investigated the influence of a classic plant secondary metabolite, allyl glucosinolate (sinigrin), and its hydrolyzed product allyl isothiocyanate (AITC), on the development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) when fed on diets with different protein-to-carbohydrate (p : c) ratios. We also examined the effects of these toxins on larval biochemistry, by chemically analyzing the frass produced by insects feeding on the different diets. As expected, AITC had a greater negative effect than sinigrin on H. armigera life-history traits. However, AITC at low concentration appeared to have a positive effect on some traits. Both sinigrin and AITC-induced detoxification activity in the gut, and the reaction was related to diet protein concentration. High-protein diets can provide the required free amino acid, especially cysteine, needed for the detoxification process. The nutrient content of the diet influences how plant secondary metabolites are handled, and the use of artificial diets in experiments investigating the metabolic fate of plant secondary compounds needs to be carefully evaluated.

The observation of starch digestion in blue mussel Mytilus galloprovincialis exposed to microplastic particles under varied food conditions

Microplastic continues to be an environmental concern, especially for filter feeding bivalves known to ingest these particles. It is important to understand the effects of microplastic particles on the physiological performance of these bivalves and many studies have investigated their impact on various physiological processes. This study investigated the effects of microplastic (10 μm) on digestive enzyme (amylase) activity of Mytilus galloprovincialis at 55,000 and 110,000 microplastic particles/L under laboratory conditions. Additionally, our study measured the expression of an isoform of Hsp70 in the gills to assess whether or not these particles may cause protein denaturation. Results revealed that this regime negatively affect the ability of M. galloprovincialis to digest starch under high food conditions but not low food conditions. Exposure to extreme levels of microplastic raised amylase activity. Furthermore, Hsp70 transcript abundance was not elevated in treatment mussels. These results show that mussels may be resilient to current microplastic pollution levels in nature.

Monoterpenoid signals and their transcriptional responses to feeding and juvenile hormone regulation in bark beetle Ips hauseri

Hauser's engraver beetle, Ips hauseri, is a serious pest in spruce forest ecosystems in Central Asia. Its monoterpenoid signal production, transcriptome responses and potential regulatory mechanisms remain poorly understood. The quality and quantity of volatile metabolites in hindgut extracts of I. hauseri were found to differ between males and females and among three groups: beetles that were newly emerged, those with a topical application of juvenile hormone III (JHIII) and those that had been feeding for 24 h. Feeding males definitively dominated monoterpenoid signal production in I. hauseri, which uses (4S)-(-)-ipsenol and (S)-(-)-cis-verbenol to implement reproductive segregation from Ipstypographus and Ipsshangrila. Feeding stimulation induced higher expression of most genes related to the biosynthesis of (4S)-(-)-ipsenol than JHIII induction, and showed a male-specific mode in I. hauseri. JHIII stimulated males to produce large amounts of (-)-verbenone and also upregulated the expression of several CYP6 genes, to a greater extent in males than in females. The expression of genes involved in the metabolism of JHIII in females and males was also found to be upregulated. Our results indicate that a species-specific aggregation pheromone system for I. hauseri, consisting of (4S)-(-)-ipsenol and S-(-)-cis-verbenol, can be used to monitor population dynamics or mass trap killing. Our results also enable a better understanding of the bottom-up role of feeding behaviors in mediating population reproduction/aggregation and interspecific interactions.

Interplay between Yersinia pestis and its flea vector in lipoate metabolism

To thrive, vector-borne pathogens must survive in the vector's gut. How these pathogens successfully exploit this environment in time and space has not been extensively characterized. Using Yersinia pestis (the plague bacillus) and its flea vector, we developed a bioluminescence-based approach and employed it to investigate the mechanisms of pathogenesis at an unprecedented level of detail. Remarkably, lipoylation of metabolic enzymes, via the biosynthesis and salvage of lipoate, increases the Y. pestis transmission rate by fleas. Interestingly, the salvage pathway's lipoate/octanoate ligase LplA enhances the first step in lipoate biosynthesis during foregut colonization but not during midgut colonization. Lastly, Y. pestis primarily uses lipoate provided by digestive proteolysis (presumably as lipoyl peptides) rather than free lipoate in blood, which is quickly depleted by the vector. Thus, spatial and temporal factors dictate the bacterium's lipoylation strategies during an infection, and replenishment of lipoate by digestive proteolysis in the vector might constitute an Achilles' heel that is exploited by pathogens.

Chemical defence in Brassicaceae against pollen beetles revealed by metabolomics and flower bud manipulation approaches

Divergence of chemical plant defence mechanisms within the Brassicaceae can be utilized to identify means against specialized pest insects. Using a bioassay-driven approach, we (a) screened 24 different Brassica napus cultivars, B. napus resyntheses and related brassicaceous species for natural plant resistance against feeding adults of the pollen beetle (Brassicogethes aeneus), (b) tested for gender-specific feeding resistance, (c) analysed the flower bud metabolomes by a non-targeted approach and (d) tested single candidate compounds for their antifeedant activity. (a) In no-choice assays, beetles were allowed to feed on intact plants. Reduced feeding activity was mainly observed on Sinapis alba and Barbarea vulgaris but not on B. napus cultivars. (b) Males fed less and discriminated more in feeding than females. (c) Correlation of the metabolite abundances with the beetles' feeding activity revealed several glucosinolates, phenylpropanoids, flavonoids and saponins as potential antifeedants. (d) These were tested in dual-bud-choice assays developed for medium-throughput compound screening. Application of standard compounds on single oilseed rape flower buds revealed highly deterrent effects of glucobarbarin, oleanolic acid and hederagenin. These results help to understand chemical plant defence in the Brassicaceae and are of key importance for further breeding strategies for insect-resistant oilseed rape cultivars.

Physiological status is a stronger predictor of nutrient selection than ambient plant nutrient content for a wild herbivore

There is generally a close relationship between a consumer's food and its optimal nutrients. When there is a mismatch, it is hypothesized that mobile herbivores switch between food items to balance nutrients, however, there are limited data for field populations. In this study, we measured ambient plant nutrient content at two time points and contrasted our results with the nutrient ratio selected by wild female and male grasshoppers (Oedaleus senegalensis). Few plants were near O. senegalensis' optimal protein:carbohydrate ratio (P:C), nor were plants complementary. Grasshoppers collected earlier all regulated for a carbohydrate-biased ratio but females ate slightly more protein. We hypothesized that the long migration undertaken by this species may explain its carbohydrate needs. In contrast to most laboratory studies, grasshoppers collected later did not tightly regulate their P:C. These results suggest that field populations are not shifting their P:C to match seasonal plant nutrient shifts and that mobile herbivores rely on post-ingestive mechanisms in the face of environmental variation. Because this is among the first studies to examine the relationship between ambient nutrient landscape and physiological state our data are a key step in bridging knowledge acquired from lab studies to hypotheses regarding the role ecological factors play in foraging strategies.

Mechanisms of Nutritional Resource Exploitation by Insects

Insects have evolved an extraordinary range of nutritional adaptations to exploit other animals, plants, bacteria, fungi and soils as resources in terrestrial and aquatic environments. This special issue provides some new insights into the mechanisms underlying these adaptations. Contributions comprise lab and field studies investigating the chemical, physiological, cognitive and behavioral mechanisms that enable resource exploitation and nutrient intake regulation in insects. The collection of papers highlights the need for more studies on the comparative sensory ecology, underlying nutritional quality assessment, cue perception and decision making to fully understand how insects adjust resource selection and exploitation in response to environmental heterogeneity and variability.

Induction of long-lived potential aestivation states in laboratory An. gambiae mosquitoes

Background

How anopheline mosquitoes persist through the long dry season in Africa remains a gap in our understanding of these malaria vectors. To span this period in locations such as the Sahelian zone of Mali, mosquitoes must either migrate to areas of permanent water, recolonize areas as they again become favorable, or survive in harsh conditions including high temperatures, low humidity, and an absence of surface water (required for breeding). Adult mosquitoes surviving through this season must dramatically extend their typical lifespan (averaging 2–3 weeks) to 7 months. Previous work has found evidence that the malaria mosquito An. coluzzii, survives over 200 days in the wild between rainy seasons in a presumed state of aestivation (hibernation), but this state has so far not been replicated in laboratory conditions. The inability to recapitulate aestivation in the lab hinders addressing key questions such as how this state is induced, how it affects malaria vector competence, and its impact on disease transmission.

Methods

In effort to induce aestivation, we held laboratory mosquitoes in climate-controlled incubators with a range of conditions that adjusted humidity (40–85% RH), temperature (18–27 °C), and light conditions (8–12 h of light) and evaluated their survivorship. These conditions were chosen to mimic the late rainy and dry seasons as well as relevant extremes these mosquitoes may experience during aestivation.

Results

We found that by priming mosquitoes in conditions simulating the late wet season in Mali, and maintaining mosquitoes in reduced light/temperature, mean mosquito survival increased from 18.34 ± 0.65 to 48.02 ± 2.87 days, median survival increased from 19 (95% CI 17–21) to 50 days (95% CI 40–58), and the maximum longevity increased from 38 to 109 days (P-adj < 0.001). While this increase falls short of the 200 + day survival seen in field mosquitoes, this extension is substantially higher than previously found through environmental or dietary modulation and is hard to reconcile with states other than aestivation. This finding will provide a platform for future characterization of this state, and allow for comparison to field collected samples.

Dung Beetle Body Condition: A Tool for Disturbance Evaluation in Contaminated Pastures

The use of veterinary medical products and herbicides is a common practice in intensified livestock systems. These compounds affect nontarget organisms that perform important ecosystem functions, such as dung beetles. The assessment of body condition allows us to determine how individuals respond to changes in the environment. However, assessments of how contamination associated with cattle farming affects coprophagous insects such as dung beetles have not been conducted in natural systems. In the present study, we evaluated the effect of ivermectin (an antiparasitic drug) and herbicides on the body condition of 3 species of dung beetles collected in the field: Copris incertus, Euoniticellus intermedius, and Digitonthophagus gazella. We recorded 3 condition indicators (body size, lipid mass, and muscle mass) of beetles collected from 19 livestock ranches in northeastern Mexico. In general, the use of ivermectin had adverse effects on C. incertus and E. intermedius whereas the effects were positive for D. gazella. Conversely, the use of herbicides had adverse effects on D. gazella and positive effects on C. incertus. The different effects of ivermectin and herbicides found in males and females show that sex can be important in determining individual responses to environmental contamination. Importantly, we provide the first evidence under natural conditions that native and exotic species of dung beetles are highly sensitive to different types of livestock management, with veterinary medications and herbicides having the ability to alter body condition. Changes in dung beetle condition can reduce the ecosystem services that dung beetles provide in livestock systems. Environ Toxicol Chem 2019;38:2392-2404. © 2019 SETAC.

Symbiotic bacteria motivate the foraging decision and promote fecundity and survival of Bactrocera dorsalis (Diptera: Tephritidae)

Background

The gut bacteria of tephritid fruit flies play prominent roles in nutrition, reproduction, maintenance and ecological adaptations of the host. Here, we adopted an approach based on direct observation of symbiotic or axenic flies feeding on dishes seeded with drops of full diet (containing all amino acids) or full diet supplemented with bacteria at similar concentrations to explore the effects of intestinal bacteria on foraging decision and fitness of Bactrocera dorsalis.

Results

The results show that intestinal probiotics elicit beneficial foraging decision and enhance the female reproduction fitness and survival of B. dorsalis (symbiotic and axenic), yet preferences for probiotic diets were significantly higher in axenic flies to which they responded faster compared to full diet. Moreover, females fed diet supplemented with Pantoea dispersa and Enterobacter cloacae laid more eggs but had shorter lifespan while female fed Enterococcus faecalis and Klebsiella oxytoca enriched diets lived longer but had lower fecundity compared to the positive control. Conversely, flies fed sugar diet (negative control) were not able to produce eggs, but lived longer than those from the positive control.

Conclusions

These results suggest that intestinal bacteria can drive the foraging decision in a way which promotes the reproduction and survival of B. dorsalis. Our data highlight the potentials of gut bacterial isolates to control the foraging behavior of the fly and empower the sterile insect technique (SIT) program through the mass rearing.

Moving to Keep Fit: Feeding Behavior and Movement of Helicoverpa armigera (Lepidoptera: Noctuidae) on Artificial Diet With Different Protein: Carbohydrate Ratios

Insect herbivores can modify their foraging behavior to obtain a balanced food intake, and they tend to move between food sources with different nutrient values. We investigated this movement in early instar larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) using a putative optimal artificial diet (OP) and high protein (HP) and high carbohydrate (HC) artificial diets based on protein (p) and carbohydrate (c) ratios. Larvae were allowed to choose between the same kind of diet cubes (effectively no-choice), or diet cubes with different p: c ratios. In no-choice tests, we found that first instar larvae remained longest on OP diet and spent the least time on HC diet, while third instar larvae remained longest on HC diet and spent least time on OP diet. First instar larvae moved the most when provided with HC diet, while third instar larvae moved most when provided with OP diet. However, both stages moved the least when allowed to choose between diet cubes with different p: c ratios. The relative growth rate decreased when larvae increased their movement, but this influence was not evident when larvae fed on HC diet. Larvae that fed only on HC diet had the highest relative growth rate, followed by larvae with access to all diets simultaneously, indicating a behavior to mix nutrient intake. We relate these findings to behavior of this major pest species under field conditions.

Bumblebees adjust protein and lipid collection rules to the presence of brood

Animals have evolved foraging strategies to acquire blends of nutrients that maximize fitness traits. In social insects, nutrient regulation is complicated by the fact that few individuals, the foragers, must address the divergent nutritional needs of all colony members simultaneously, including other workers, the reproductives, and the brood. Here we used 3D nutritional geometry design to examine how bumblebee workers regulate their collection of 3 major macronutrients in the presence and absence of brood. We provided small colonies artificial nectars (liquid diets) and pollens (solid diets) varying in their compositions of proteins, lipids, and carbohydrates during 2 weeks. Colonies given a choice between nutritionally complementary diets self-selected foods to reach a target ratio of 71% proteins, 6% carbohydrates, and 23% lipids, irrespective of the presence of brood. When confined to a single nutritionally imbalanced solid diet, colonies without brood regulated lipid collection and over-collected protein relative to this target ratio, whereas colonies with brood regulated both lipid and protein collection. This brood effect on the regulation of nutrient collection by workers suggests that protein levels are critical for larval development. Our results highlight the importance of considering bee nutrition as a multidimensional phenomenon to better assess the effects of environmental impoverishment and malnutrition on population declines.

A First Attempt to Produce Proteins from Insects by Means of a Circular Economy

Simple Summary

Protein production for animal husbandry is a crucial ecological problem because of its impact on the environment, as it requires water, energy, and land. These resources are limited and not reusable. In this study, we obtained a continuously regenerating system in which by-products of a process constituted rough material for another one. Leftovers from fruit and vegetable markets were employed as rearing substrate for insects (Black Soldier Fly). Insect biomass was transformed into meal and oil for fish feeding and food/pharmaceutical industry, respectively. The residuals from insect rearing were then used as substrate to grow earthworms, which transformed this material into compost for plants. Therefore, we returned to the starting point of our economic and ecological closed loop, i.e., to soil improvers (nutrient material) for fruit and vegetable production. Moreover, earthworms can be conveniently employed as fishing bites. We also studied a series of physiological parameters of the living organisms involved in this system to verify their health conditions (insects), and growth performances (insects and fish). Microbiological analyses of insects, rearing substrate, and insect meal were conducted to assess their safety for fish and humans. Related technological processes, such as insects drying, grinding, and oil extraction, were also tested.

Abstract

The worldwide growing consumption of proteins to feed humans and animals has drawn a considerable amount of attention to insect rearing. Insects reared on organic wastes and used as feed for monogastric animals can reduce the environmental impact and increase the sustainability of meat/fish production. In this study, we designed an environmentally closed loop for food supply in which fruit and vegetable waste from markets became rearing substrate for Hermetia illucens (BSF— black soldier fly). A vegetable and fruit-based substrate was compared to a standard diet for Diptera in terms of larval growth, waste reduction index, and overall substrate degradation. Morphological analysis of insect organs was carried out to obtain indications about insect health. Processing steps such as drying and oil extraction from BSF were investigated. Nutritional and microbiological analyses confirmed the good quality of insects and meal. The meal was then used to produce fish feed and its suitability to this purpose was assessed using trout. Earthworms were grown on leftovers of BSF rearing in comparison to a standard substrate. Chemical analyses of vermicompost were performed. The present research demonstrates that insects can be used to reduce organic waste, increasing at the same time the sustainability of aquaculture and creating interesting by-products through the linked bio-system establishment.

Developmental stage-dependent response and preference for host plant quality in an insect herbivore

Larval-derived nutritional reserves are essential in shaping insects' adult fitness. Early larval instars of many Lepidopteran species are often sessile, and the conditions experienced by these larvae are often highly dependent on the mother's oviposition choice. Later larval stages are more mobile and therefore can choose their food whenever alternatives are available. We tested how feeding on a drought-exposed host plant impacts life history in an insect herbivore, and whether the observed responses depended on developmental stage. We used drought to alter host plant quality of the ribwort plantain, Plantago lanceolata, and assessed whether host plant preference of postdiapause larvae and adult females increased their own or their offspring's performance, respectively, in the Glanville fritillary butterfly, Melitaea cinxia. Larval response to drought-exposed host plants varied with developmental stage: early larval stages (prediapause) had decreased survival and body mass on drought-exposed plants, while later larval stages (postdiapause) developed faster, weighed more and had a higher growth rate on the drought-exposed plants. Postdiapause larvae also showed a preference for drought-exposed host plants, i.e. those that increased their performance, but only when fed on well-watered host plants. Adult females, on the other hand, showed an oviposition preference for well-watered plants, hence matching the performance of their prediapause but not their postdiapause offspring. Our results highlight how variation in environmental conditions generates stage-specific responses in insects. Individuals fine-tune their own or their offspring's diet by behavioural adjustments when variation in host plant quality is available.

Intestinal bacteria modulate the foraging behavior of the oriental fruit fly Bactrocera dorsalis (Diptera: Tephritidae)

The gut microbiome of insects directly or indirectly affects the metabolism, immune status, sensory perception and feeding behavior of its host. Here, we examine the hypothesis that in the oriental fruit fly (Bactrocera dorsalis, Diptera: Tephritidae), the presence or absence of gut symbionts affects foraging behavior and nutrient ingestion. We offered protein-starved flies, symbiotic or aposymbiotic, a choice between diets containing all amino acids or only the non-essential ones. The different diets were presented in a foraging arena as drops that varied in their size and density, creating an imbalanced foraging environment. Suppressing the microbiome resulted in significant changes of the foraging behavior of both male and female flies. Aposymbiotic flies responded faster to the diets offered in experimental arenas, spent more time feeding, ingested more drops of food, and were constrained to feed on time-consuming patches (containing small drops of food), when these offered the full complement of amino acids. We discuss these results in the context of previous studies on the effect of the gut microbiome on host behavior, and suggest that these be extended to the life history dimension.

Exploring Interactions between the Gut Microbiota and Social Behavior through Nutrition

Microbes influence a wide range of host social behaviors and vice versa. So far, however, the mechanisms underpinning these complex interactions remain poorly understood. In social animals, where individuals share microbes and interact around foods, the gut microbiota may have considerable consequences on host social interactions by acting upon the nutritional behavior of individual animals. Here we illustrate how conceptual advances in nutritional ecology can help the study of these processes and allow the formulation of new empirically testable predictions. First, we review key evidence showing that gut microbes influence the nutrition of individual animals, through modifications of their nutritional state and feeding decisions. Next, we describe how these microbial influences and their social consequences can be studied by modelling populations of hosts and their gut microbiota into a single conceptual framework derived from nutritional geometry. Our approach raises new perspectives for the study of holobiont nutrition and will facilitate theoretical and experimental research on the role of the gut microbiota in the mechanisms and evolution of social behavior.

Social nutrition: an emerging field in insect science

Nutrition is thought to be a major driver of social evolution, yet empirical support for this hypothesis is scarce. Here we illustrate how conceptual advances in nutritional ecology illuminate some of the mechanisms by which nutrition mediates social interactions in insects. We focus on experiments and models of nutritional geometry and argue that they provide a powerful means for comparing nutritional phenomena across species exhibiting various social ecologies. This approach, initially developed to study the nutritional behaviour of individual insects, has been increasingly used to study insect groups and societies, leading to the emerging field of social nutrition. We discuss future directions for exploring how these nutritional mechanisms may influence major social transitions in insects and other animals.

Seeking salt: herbivorous prairie insects can be co-limited by macronutrients and sodium

The canonical factors typically thought to determine herbivore community structure often explain only a small fraction of the variation in herbivore abundance and diversity. We tested how macronutrients and relatively understudied micronutrients interacted to influence the structure of insect herbivore (orthopteran) communities. We conducted a factorial fertilisation experiment manipulating macronutrients (N and P, added together) and micronutrients (Ca, Na and K) in large plots (30 × 30 m² ) in a Texas coastal prairie. Although no single or combination of micronutrients affected herbivore communities in the absence of additional macronutrients, macronutrients and sodium added together increased herbivore abundance by 60%, richness by 15% and diversity by 20%. These results represent the first large-scale manipulation of single micronutrients and macronutrients in concert, and revealed an herbivore community co-limited by macronutrients and Na. Our work supports an emerging paradigm that Na may be important in limiting herbivore communities.

Caught in the web: Spider web architecture affects prey specialization and spider-prey stoichiometric relationships

Quantitative approaches to predator-prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator-prey interactions. Here, we used spider-prey interactions as a model system to investigate whether different spider web architectures-orb, tangle, and sheet-tangle-affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle-web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet-tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle-web spiders than for orb and sheet-tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator-prey interactions.

Nutritional ecology and foraging theory

Historically, two fields of research have developed theory around foraging and feeding that have influenced biology more broadly, optimal foraging theory and nutritional ecology. While these fields have developed largely in parallel, they are complementary with each offering particular strengths. Here we show how an approach developed in the study of insect nutrition, called nutritional geometry, has provided a framework for incorporating key aspects of optimal foraging theory into nutritional ecology. This synthesis provides a basis for integrating with foraging and feeding the many facets of biology that are linked to nutrition and is now influencing diverse areas of the biological and biomedical sciences.

Viral exposure effects on life-history, flight-related traits, and wing melanisation in the Glanville fritillary butterfly

Infections represent a constant threat for organisms and can lead to substantial fitness losses. Understanding how individuals, especially from natural populations, respond towards infections is thus of great importance. Little is known about immunity in the Glanville fritillary butterfly (Melitaea cinxia). As the larvae live gregariously in family groups, vertical and horizontal transmission of infections could have tremendous effects on individuals and consequently impact population dynamics in nature. We used the Alphabaculovirus type strain Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and demonstrated that positive concentration-dependent baculovirus exposure leads to prolonged developmental time and decreased survival during larval and pupal development, with no sex specific differences. Viral exposure did not influence relative thorax mass or wing morphometric traits often related to flight ability, yet melanisation of the wings increased with viral exposure, potentially influencing disease resistance or flight capacity via thermal regulation. Further research is needed to explore effects under sub-optimal conditions, determine effects on fitness-related traits, and investigate a potential adaptive response of increased melanisation in the wings due to baculovirus exposure.

A theoretical exploration of dietary collective medication in social insects

Animals often alter their food choices following a pathogen infection in order to increase immune function and combat the infection. Whether social animals that collect food for their brood or nestmates adjust their nutrient intake to the infection states of their social partners is virtually unexplored. Here we develop an individual-based model of nutritional geometry to examine the impact of collective nutrient balancing on pathogen spread in a social insect colony. The model simulates a hypothetical social insect colony infected by a horizontally transmitted parasite. Simulation experiments suggest that collective nutrition, by which foragers adjust their nutrient intake to simultaneously address their own nutritional needs as well as those of their infected nestmates, is an efficient social immunity mechanism to limit contamination when immune responses are short. Impaired foraging in infected workers can favour colony resilience when pathogen transmission rate is low (by reducing contacts with the few infected foragers) or trigger colony collapse when transmission rate is fast (by depleting the entire pool of foragers). Our theoretical examination of dietary collective medication in social insects suggests a new possible mechanism by which colonies can defend themselves against pathogens and provides a conceptual framework for experimental investigations of the nutritional immunology of social animals.

Collective foraging in spatially complex nutritional environments

Nutrition impinges on virtually all aspects of an animal's life, including social interactions. Recent advances in nutritional ecology show how social animals often trade-off individual nutrition and group cohesion when foraging in simplified experimental environments. Here, we explore how the spatial structure of the nutritional landscape influences these complex collective foraging dynamics in ecologically realistic environments. We introduce an individual-based model integrating key concepts of nutritional geometry, collective animal behaviour and spatial ecology to study the nutritional behaviour of animal groups in large heterogeneous environments containing foods with different abundance, patchiness and nutritional composition. Simulations show that the spatial distribution of foods constrains the ability of individuals to balance their nutrient intake, the lowest performance being attained in environments with small isolated patches of nutritionally complementary foods. Social interactions improve individual regulatory performances when food is scarce and clumpy, but not when it is abundant and scattered, suggesting that collective foraging is favoured in some environments only. These social effects are further amplified if foragers adopt flexible search strategies based on their individual nutritional state. Our model provides a conceptual and predictive framework for developing new empirically testable hypotheses in the emerging field of social nutrition.This article is part of the themed issue 'Physiological determinants of social behaviour in animals'.

Feeding Immunity: Physiological and Behavioral Responses to Infection and Resource Limitation

Resources are a core currency of species interactions and ecology in general (e.g., think of food webs or competition). Within parasite-infected hosts, resources are divided among the competing demands of host immunity and growth as well as parasite reproduction and growth. Effects of resources on immune responses are increasingly understood at the cellular level (e.g., metabolic predictors of effector function), but there has been limited consideration of how these effects scale up to affect individual energetic regimes (e.g., allocation trade-offs), susceptibility to infection, and feeding behavior (e.g., responses to local resource quality and quantity). We experimentally rewilded laboratory mice (strain C57BL/6) in semi-natural enclosures to investigate the effects of dietary protein and gastrointestinal nematode (Trichuris muris) infection on individual-level immunity, activity, and behavior. The scale and realism of this field experiment, as well as the multiple physiological assays developed for laboratory mice, enabled us to detect costs, trade-offs, and potential compensatory mechanisms that mice employ to battle infection under different resource conditions. We found that mice on a low-protein diet spent more time feeding, which led to higher body fat stores (i.e., concentration of a satiety hormone, leptin) and altered metabolite profiles, but which did not fully compensate for the effects of poor nutrition on albumin or immune defenses. Specifically, immune defenses measured as interleukin 13 (IL13) (a primary cytokine coordinating defense against T. muris) and as T. muris-specific IgG1 titers were lower in mice on the low-protein diet. However, these reduced defenses did not result in higher worm counts in mice with poorer diets. The lab mice, living outside for the first time in thousands of generations, also consumed at least 26 wild plant species occurring in the enclosures, and DNA metabarcoding revealed that the consumption of different wild foods may be associated with differences in leptin concentrations. When individual foraging behavior was accounted for, worm infection significantly reduced rates of host weight gain. Housing laboratory mice in outdoor enclosures provided new insights into the resource costs of immune defense to helminth infection and how hosts modify their behavior to compensate for those costs.