Ants Disinfect Fungus-Exposed Brood by Oral Uptake and Spread of Their Poison

Social organization of necrophoresis: insights into disease risk management in ant societies

Insect societies, which are at a high risk of disease outbreaks, have evolved sanitary strategies that contribute to their social immunity. Here, we investigated in the red ant Myrmica rubra, how the discarding of nestmate cadavers is socially organized depending on the associated pathogenicity. We examined whether necrophoresis is carried out by a specific functional group of workers or by any nestmates that may become short-term specialists. By observing the behavioural profiles of tagged individuals, we assigned half of the colony members to functional groups (foragers, intermittent-foragers, domestics, nurses and inactives). Following the introduction of uninfected or sporulating corpses into the nest, intermittent-foragers were the functional group most involved in necrophoresis, as they touched, moved and discarded more cadavers. Interestingly, sporulating corpses induced a more generalized response in workers from all functional groups, thereby accelerating their rejection from the nest. The individuals contacting corpses were also prophylactically engaged in more grooming behaviour, suggesting the existence of hygienist workers within ant colonies. These findings raise questions about a trade-off existing between concentrating health risks on a few workers who are highly specialized in necrophoresis and exposing a larger population of nestmates who cooperate to speed up nest sanitization.

Benefits of extended maternal care in a mass-provisioning bee at the cusp of sociality

Many invertebrates exhibit parental care, posited as a precursor to sociality. For example, solitary foundresses of the facultative social orchid bee Euglossa viridissima guard their brood for 6+ weeks before offspring emerge, when the nest may become social. Guarding comes at the fitness cost of foregoing the production of additional offspring. Yet it is unclear whether guarding (extended maternal care) can enhance offspring survival such that it outweighs those fitness costs, or if it is a consequence of the selective benefits of sociality, including extended female longevity. Experimental removal of solitary foundresses from nests of E. viridissima revealed an immediate fitness loss: decreased offspring survival. A mathematical model exploring the trade-off between extended maternal care versus non-guarding revealed that extended maternal care is immediately advantageous to a solitary mother if nest establishment takes longer than a threshold 1.7-12.5 days. Below this threshold, our model suggests that social fitness gains (acquiring helper daughters) need to be invoked to explain the evolution of extended maternal care. Enhanced survival of offspring through guarding and nest inheritance may nevertheless ease conditions for the evolution of sociality by favouring extended adult longevity and brood care in incipient social species like E. viridissima.

Fungus Fighters: Wood Ants (Formica polyctena) and Their Associated Microbes Inhibit Plant Pathogenic Fungi

Plant diseases cost the global economy billions of US dollars every year. The problem has mainly been addressed by using chemical pesticides, but recently, the use of ants has shown promising effects against plant pathogens. However, the mechanisms accounting for these effects have not yet been determined. One possible explanation is antimicrobial microorganisms associated with ants. Through controlled laboratory experiments, we investigated the inhibitory effects of wood ants (Formica polyctena) and their associated microorganisms against economically important plant pathogenic fungi. All live ants, extracts from crushed ants, and extracts from washed ants significantly inhibited the apple brown rot (Monilinia fructigena) while yielding the growth of other microbes. Furthermore, all investigated wood ants transferred microorganisms to their surroundings within 10 s when walking across a surface. We isolated the most dominant microorganisms deposited by walking ants and from washed ant extracts (i.e., strains likely found on the surface of ants), resulting in four bacterial cultures and one yeast. Two of these isolates, strain I3 (most closely related to Pseudomonas sichuanensis and P. entomophila) and strain I1b (most closely related to Bacillus mycoides), showed inhibitory effects against apple brown rot and apple scab (Venturia inaequalis), while strain I3 also inhibited gray mold (Botrytis cinerea) and Fusarium head blight (Fusarium graminearum). These results suggest that wood ants have potential as biological control agents against commercially relevant plant pathogens, and that their inhibitory effect might be at least partially caused by antibiotic compounds produced by their associated microorganisms.

Pathogen-specific social immunity is associated with erosion of individual immune function in an ant

Contagious diseases are a major threat to societies in which individuals live in close contact. Social insects have evolved collective defense behaviors, such as social care or isolation of infected workers, that prevent outbreaks of pathogens. It has thus been suggested that individual immunity is reduced in species with such 'social immunity'. However, this hypothesis has not been tested functionally. Here, we characterize the immune response of the ant Lasius niger using a combination of genomic analysis, experimental infections, gene expression quantification, behavioural observations and pathogen quantifications. We uncover a striking specialization of immune responses towards different pathogens. Systemic individual immunity is effective against opportunistic bacterial infections, which are not covered by social immunity, but is not elicited upon fungal infections, which are effectively controlled by social immunity. This specialization suggests that immune layers have evolved complementary functions predicted to ensure the most cost-effective response against a wide range of pathogens.

Social life results in social stress protection: a novel concept to explain individual life-history patterns in social insects

Resistance to and avoidance of stress slow aging and confer increased longevity in numerous organisms. Honey bees and other superorganismal social insects have two main advantages over solitary species to avoid or resist stress: individuals can directly help each other by resource or information transfer, and they can cooperatively control their environment. These benefits have been recognised in the context of pathogen and parasite stress as the concept of social immunity, which has been extensively studied. However, we argue that social immunity is only a special case of a general concept that we define here as social stress protection to include group-level defences against all biotic and abiotic stressors. We reason that social stress protection may have allowed the evolution of reduced individual-level defences and individual life-history optimization, including the exceptional aging plasticity of many social insects. We describe major categories of stress and how a colonial lifestyle may protect social insects, particularly against temporary peaks of extreme stress. We use the honey bee (Apis mellifera L.) to illustrate how patterns of life expectancy may be explained by social stress protection and how modern beekeeping practices can disrupt social stress protection. We conclude that the broad concept of social stress protection requires rigorous empirical testing because it may have implications for our general understanding of social evolution and specifically for improving honey bee health.

The Budding Neuroscience of Ant Social Behavior

Ant physiology has been fashioned by 100 million years of social evolution. Ants perform many sophisticated social and collective behaviors yet possess nervous systems similar in schematic and scale to that of the fruit fly Drosophila melanogaster, a popular solitary model organism. Ants are thus attractive complementary subjects to investigate adaptations pertaining to complex social behaviors that are absent in flies. Despite research interest in ant behavior and the neurobiological foundations of sociality more broadly, our understanding of the ant nervous system is incomplete. Recent technical advances have enabled cutting-edge investigations of the nervous system in a fashion that is less dependent on model choice, opening the door for mechanistic social insect neuroscience. In this review, we revisit important aspects of what is known about the ant nervous system and behavior, and we look forward to how functional circuit neuroscience in ants will help us understand what distinguishes solitary animals from highly social ones.

Social evolution: Limb amputation prevents infection in ants

Social insect workers, renowned for their altruism, are frequently perceived as 'disposable'. A new study finds that ants amputate the limbs of nestmates, which saves them from infection, and indicates that worker care is as critical to colony success as sacrifice.

Gut-brain axis: A cutting-edge approach to target neurological disorders and potential synbiotic application

The microbiota-gut-brain axis (MGBA) represents a sophisticated communication network between the brain and the gut, involving immunological, endocrinological, and neural mediators. This bidirectional interaction is facilitated through the vagus nerve, sympathetic and parasympathetic fibers, and is regulated by the hypothalamic-pituitary-adrenal (HPA) axis. Evidence shows that alterations in gut microbiota composition, or dysbiosis, significantly impact neurological disorders (NDs) like anxiety, depression, autism, Parkinson's disease (PD), and Alzheimer's disease (AD). Dysbiosis can affect the central nervous system (CNS) via neuroinflammation and microglial activation, highlighting the importance of the microbiota-gut-brain axis (MGBA) in disease pathogenesis. The microbiota influences the immune system by modulating chemokines and cytokines, impacting neuronal health. Synbiotics have shown promise in treating NDs by enhancing cognitive function and reducing inflammation. The gut microbiota's role in producing neurotransmitters and neuroactive compounds, such as short-chain fatty acids (SCFAs), is critical for CNS homeostasis. Therapeutic interventions targeting the MGBA, including dietary modulation and synbiotic supplementation, offer potential benefits for managing neurodegenerative disorders. However, more in-depth clinical studies are necessary to fully understand and harness the therapeutic potential of the MGBA in neurological health and disease.

Uncovering the function of insulin receptor substrate in termites' immunity through active immunization

Insulin receptor substrate (IRS) proteins are key mediators in insulin signaling pathway. In social insect lives, IRS proteins played important roles in caste differentiation and foraging, but there function in disease defenses such as active immunization has not been reported yet. To investigate the issue, we successfully suppressed the IRS gene 3 days after dsRNA injection. Suppressing IRS gene increased the contents of glucose, trehalose, glycogen, and triglyceride and decreased the content of pyruvate in termites, and led to the metabolic disorder of glucose and lipids. IRS suppressing significantly enhanced grooming behaviors of nestmates of fungus-contaminated termites and hence increased the conidial load in the guts of the nestmates. Additionally, IRS suppressing led to significant downregulation of the immune genes Gram-negative bacteria-binding protein2 (GNBP2) and termicin and upregulation of the apoptotic gene caspase8, and hence diminished antifungal activity of nestmates of fungus-contaminated termites. The above abnormal behavioral and physiological responses significantly decreased the survival rate of dsIRS-injected nestmates of the fungus-contaminated termites. These findings suggest that IRS is involved in regulation of active immunization in termites, providing a better understanding of the link between insulin signaling and the social immunity of termites.

Dynamics and drivers of fungal communities in a multipartite ant-plant association

BACKGROUND

Fungi and ants belong to the most important organisms in terrestrial ecosystems on Earth. In nutrient-poor niches of tropical rainforests, they have developed steady ecological relationships as a successful survival strategy. In tropical ant-plant mutualisms worldwide, where resident ants provide the host plants with defense and nutrients in exchange for shelter and food, fungi are regularly found in the ant nesting space, inhabiting ant-made dark-colored piles ("patches"). Unlike the extensively investigated fungus-growing insects, where the fungi serve as the primary food source, the purpose of this ant-fungi association is less clear. To decipher the roles of fungi in these structures within ant nests, it is crucial to first understand the dynamics and drivers that influence fungal patch communities during ant colony development.

RESULTS

In this study, we investigated how the ant colony age and the ant-plant species affect the fungal community in the patches. As model we selected one of the most common mutualisms in the Tropics of America, the Azteca-Cecropia complex. By amplicon sequencing of the internal transcribed spacer 2 (ITS2) region, we analyzed the patch fungal communities of 93 Azteca spp. colonies inhabiting Cecropia spp. trees. Our study demonstrates that the fungal diversity in patches increases as the ant colony grows and that a change in the prevalent fungal taxa occurs between initial and established patches. In addition, the ant species significantly influences the composition of the fungal community in established ant colonies, rather than the host plant species.

CONCLUSIONS

The fungal patch communities become more complex as the ant colony develops, due to an acquisition of fungi from the environment and a substrate diversification. Our results suggest a successional progression of the fungal communities in the patches during ant colony growth and place the ant colony as the main driver shaping such communities. The findings of this study demonstrate the unexpectedly complex nature of ant-plant mutualisms in tropical regions at a micro scale.

Do They Know What They Are Doing? Cognitive Aspects of Rescue Behaviour Directed by Workers of the Red Wood Ant Formica polyctena to Nestmate Victims Entrapped in Artificial Snares

Ant rescue behaviour belongs to the most interesting subcategories of prosocial and altruistic behaviour encountered in the animal world. Several studies suggested that ants are able to identify what exactly restrains the movements of another individual and to direct their rescue behaviour precisely to that object. To shed more light on the question of how precise the identification of the source of restraint of another ant is, we investigated rescue behaviour of red wood ant Formica polyctena workers, using a new version of an artificial snare bioassay in which a nestmate victim bore two wire loops on its body, one (acting as a snare) placed on its petiole and an additional one on its leg. The tested ants did not preferentially direct their rescue behaviour towards the snare. Moreover, the overall strategy adopted by the most active rescuers was not limited to precisely targeted rescue attempts directed towards the snare, but consisted of frequent switching between various subcategories of rescue behaviour. These findings highlight the importance of precise identification of cognitive processes and overall behavioural strategies for better understanding of causal factors underlying animal helping behaviour in light of new facts discovered by testing of various successive research hypotheses.

Insects' essential role in understanding and broadening animal medication

Like humans, animals use plants and other materials as medication against parasites. Recent decades have shown that the study of insects can greatly advance our understanding of medication behaviors. The ease of rearing insects under laboratory conditions has enabled controlled experiments to test critical hypotheses, while their spectrum of reproductive strategies and living arrangements - ranging from solitary to eusocial communities - has revealed that medication behaviors can evolve to maximize inclusive fitness through both direct and indirect fitness benefits. Studying insects has also demonstrated in some cases that medication can act through modulation of the host's innate immune system and microbiome. We highlight outstanding questions, focusing on costs and benefits in the context of inclusive host fitness.

Fungal infection alters collective nutritional intake of ant colonies

In animals, parasitic infections impose significant fitness costs.1,2,3,4,5,6 Infected animals can alter their feeding behavior to resist infection,7,8,9,10,11,12 but parasites can manipulate animal foraging behavior to their own benefits.13,14,15,16 How nutrition influences host-parasite interactions is not well understood, as studies have mainly focused on the host and less on the parasite.9,12,17,18,19,20,21,22,23 We used the nutritional geometry framework24 to investigate the role of amino acids (AA) and carbohydrates (C) in a host-parasite system: the Argentine ant, Linepithema humile, and the entomopathogenic fungus, Metarhizium brunneum. First, using 18 diets varying in AA:C composition, we established that the fungus performed best on the high-amino-acid diet 1:4. Second, we found that the fungus reached this optimal diet when given various diet pairings, revealing its ability to cope with nutritional challenges. Third, we showed that the optimal fungal diet reduced the lifespan of healthy ants when compared with a high-carbohydrate diet but had no effect on infected ants. Fourth, we revealed that infected ant colonies, given a choice between the optimal fungal diet and a high-carbohydrate diet, chose the optimal fungal diet, whereas healthy colonies avoided it. Lastly, by disentangling fungal infection from host immune response, we demonstrated that infected ants foraged on the optimal fungal diet in response to immune activation and not as a result of parasite manipulation. Therefore, we revealed that infected ant colonies chose a diet that is costly for survival in the long term but beneficial in the short term-a form of collective self-medication.

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

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

Morphology of the Mandibular and Intramandibular Glands of Army Ant Workers of Labidus praedator (Smith 1858) and Labidus coecus (Latreille 1802) (Formicidae: Dorylinae)

Social insects are characterized by having a wide diversity of exocrine glands, with highlights for ants with about 85 glands spreading throughout the body. The mandibular and intramandibular glands are associated with the production of pheromones. The army ants (Dorylinae) play an important role in the structure of the invertebrate community because they are efficient predators and provide suitable conditions for various animals following their invasions in the food search. Labidus coecus (Latreille) is an underground-ameliorating ant and Labidus praedator (Smith) is a generalist surface predator which can deplete invertebrate biomass by up to 75%. This work investigated the morphology of the mandibular and intramandibular glands of L. praedator and L. coecus workers. The glands were analyzed by light microscopy, histochemistry, and scanning electron microscopy. The mandibular and intramandibular glands of the two species were classified as class III glands. The data on the morphology of the mandibular glands has revealed that they have characteristics in common with other subfamilies. The intramandibular glands of the two species of Labidus have similar morphology and chemical composition, which indicates that the components of these glands can have the same function despite their different habits.

Bacterial diversity in arboreal ant nesting spaces is linked to colony developmental stage

The omnipresence of ants is commonly attributed to their eusocial organization and division of labor, however, bacteria in their nests may facilitate their success. Like many other arboreal ants living in plant-provided cavities, Azteca ants form dark-colored "patches" in their nesting space inside Cecropia host plants. These patches are inhabited by bacteria, fungi and nematodes and appear to be essential for ant colony development. Yet, detailed knowledge of the microbial community composition and its consistency throughout the life cycle of ant colonies was lacking. Amplicon sequencing of the microbial 16S rRNA genes in patches from established ant colonies reveals a highly diverse, ant species-specific bacterial community and little variation within an individual ant colony, with Burkholderiales, Rhizobiales and Chitinophagales being most abundant. In contrast, bacterial communities of early ant colony stages show low alpha diversity and no ant species-specific community composition. We suggest a substrate-caused bottleneck after vertical transmission of the bacterial patch community from mother to daughter colonies. The subsequent ecological succession is driven by environmental parameters and influenced by ant behavior. Our study provides key information for future investigations determining the functions of these bacteria, which is essential to understand the ubiquity of such patches among arboreal ants.

Control of pest ants by pathogenic fungi: state of the art

Pest ants are known for their damage to biodiversity, harm to agriculture, and negative impact on human welfare. Ants thrive when environmental opportunities arise, becoming pests and/or invading non-native areas. As social insects, they are extremely difficult to control using sustainable methods like biological control. The latter, although safer to the environment, acts slowly allowing the ants to use their individual and social defenses. Among biocontrol agents, fungal pathogens were proposed as promising, however, it is difficult to ascertain their success when the bibliography has not been reviewed and condensed. Therefore, this paper is the first in performing such task by analyzing publications mainly from 2000 to 2022 about the control of pest ants by fungi. From 85 publications selected, 77% corresponded to laboratory studies. Beauveria and Metarhizium were the genera most used in laboratory and field studies. Most of them included Acromyrmex and Atta leaf-cutter ants (LCA), and Solenopsis fire ants. From laboratory experiments, we evaluated how ant net mortality was affected by ant and fungal species, and also by origin, concentration, and inoculation technique of the fungal strains tested. Beauveria bassiana and Metarhizium anisopliae produced the greatest mortality, along with the inoculation spray technique and fungal strains collected from ants. There was a positive relationship between ant mortality and fungal concentration only for those studies which evaluated more than one concentration. Twenty field experimental studies were found, covering 13 pest species, mainly LCA and Solenopsis invicta. Only B. bassiana was tested on Solenopsis, M. anisopliae was mostly used for Acromyrmex, and M. anisopliae or Trichoderma were mainly used with Atta species. The median control field efficiency varied from 20% to 85% for different fungi and ant genera. When grouping all fungal species together, the median control efficiency seemed to be better for Acromyrmex (67%) than for Atta and Solenopsis (both 43%). Our review shows that, at this stage of knowledge, it is very difficult to extrapolate any result. We offer suggestions to improve and standardize laboratory and field experimental studies in order to advance more efficiently in the fungal control of pest ants.

Fungi as mutualistic partners in ant-plant interactions

Associations between fungi and ants living in mutualistic relationship with plants ("plant-ants") have been known for a long time. However, only in recent years has the mutualistic nature, frequency, and geographical extent of associations between tropical arboreal ants with fungi of the ascomycete order Chaetothyriales and Capnodiales (belonging to the so-called "Black Fungi") become clear. Two groups of arboreal ants displaying different nesting strategies are associated with ascomycete fungi: carton-building ants that construct nest walls and galleries on stems, branches or below leaves which are overgrown by fungal hyphae, and plant-ants that make their nests inside living plants (myrmecophytes) in plant provided cavities (domatia) where ants cultivate fungi in small delimited "patches". In this review we summarize the current knowledge about these unsuspected plant-ant-fungus interactions. The data suggest, that at least some of these ant-associated fungi seem to have coevolved with ants over a long period of time and have developed specific adaptations to this lifestyle.

The arylsulfatase- and phospholipase-rich venom of the plutoniumid centipede Theatops posticus

Research on centipede venoms has led to the discovery of a diverse array of novel proteins and peptides, including those with homology to previously discovered toxin families (e.g., phospholipase A2s and pM12a metalloproteases) and novel toxin families not previously detected in venoms (e.g., β-pore forming toxins and scoloptoxins). Most of this research has focused on centipedes in the order Scolopendromorpha, particularly those in the families Scolopendridae, Cryptopidae, and Scolopocryptopidae. To generate the first high-throughput venom characterization for a centipede in the scolopendromorph family Plutoniumidae, we performed venom-gland transcriptomics and venom proteomics on two Theatops posticus. We identified a total of 64 venom toxins, 60 of which were detected in both the venom-gland transcriptome and venom proteome and four of which were only detected transcriptomically. We detected a single highly abundant arylsulfatase B (ARSB) toxin, the first ARSB toxin identified from centipede venoms. As ARSBs have been detected in other venomous species (e.g., scorpions), ARSBs in T. posticus highlights a new case of convergent evolution across venoms. Theatops posticus venom also contained a much higher abundance and diversity of phospholipase A2 toxins compared to other characterized centipede venoms. Conversely, we detected other common centipedes toxins, such as CAPs and scoloptoxins, at relatively low abundances and diversities. Our observation of a diverse set of toxins from T. posticus venom, including those from novel toxin families, emphasizes the importance of studying unexplored centipede taxonomic groups and the continued potential of centipede venoms for novel toxin discovery and unraveling the molecular mechanisms underlying trait evolution.

Chemistry and Functions of Imported Fire Ant Venom

In the United States, imported fire ants are often referred to as red imported fire ants, Solenopsis invicta Buren, black imported fire ants, S. richteri Forel, and their hybrid (S. invicta × S. richteri). Due to their aggressive stings and toxic venom, imported fire ants pose a significant threat to public health, agriculture, and ecosystem health. However, venom plays a vital role in the survival of fire ants by serving various crucial functions in defense, foraging, and colony health maintenance. Numerous reviews and book chapters have been published on fire ant venom. Due to its medical importance and the expanding global distribution of these ants, fire ant venom research remains an active and highly productive area, leading to the discovery of new components and functions. This review summarizes the recent advances in our understanding of fire ant venom chemistry and its functions within fire ant colonies.

Dynamic pathogen detection and social feedback shape collective hygiene in ants

Cooperative disease defense emerges as group-level collective behavior, yet how group members make the underlying individual decisions is poorly understood. Using garden ants and fungal pathogens as an experimental model, we derive the rules governing individual ant grooming choices and show how they produce colony-level hygiene. Time-resolved behavioral analysis, pathogen quantification, and probabilistic modeling reveal that ants increase grooming and preferentially target highly-infectious individuals when perceiving high pathogen load, but transiently suppress grooming after having been groomed by nestmates. Ants thus react to both, the infectivity of others and the social feedback they receive on their own contagiousness. While inferred solely from momentary ant decisions, these behavioral rules quantitatively predict hour-long experimental dynamics, and synergistically combine into efficient colony-wide pathogen removal. Our analyses show that noisy individual decisions based on only local, incomplete, yet dynamically-updated information on pathogen threat and social feedback can lead to potent collective disease defense.

Transcriptomics Reveals the Killing Mechanism by Which Entomopathogenic Fungi Manipulate the RNA Expression Profiles of Termites and Provides Inspiration for Green Pest Management

As chemical pesticides have caused serious environmental pollution, fungus-based biological control has become a developing alternative to chemical control. Here, we aimed to determine the molecular mechanism underlying how Metarhizium anisopliae facilitated invasive infection. We found that the fungus increased its virulence by downregulating glutathione S-transferase (GST) and superoxide dismutase (SOD) throughout termite bodies. Among 13 fungus-induced microRNAs throughout termite bodies, miR-7885-5p and miR-252b upregulation significantly downregulated several mRNAs in response to toxic substances to increase the fungal virulence [e.g., phosphoenolpyruvate carboxykinase (GTP) and heat shock protein homologue SSE1]. In addition, nanodelivered small interfering RNA of GST and SOD and miR-7885-5p and miR-252b mimics increased the virulence of the fungus. These findings provide new insights into the killing mechanism of entomopathogens and their utilization of the host miRNA machinery to reduce host defenses, laying the groundwork to enhance virulence of biocontrol agents for green pest management.

Pathogen evasion of social immunity

Treating sick group members is a hallmark of collective disease defence in vertebrates and invertebrates alike. Despite substantial effects on pathogen fitness and epidemiology, it is still largely unknown how pathogens react to the selection pressure imposed by care intervention. Using social insects and pathogenic fungi, we here performed a serial passage experiment in the presence or absence of colony members, which provide social immunity by grooming off infectious spores from exposed individuals. We found specific effects on pathogen diversity, virulence and transmission. Under selection of social immunity, pathogens invested into higher spore production, but spores were less virulent. Notably, they also elicited a lower grooming response in colony members, compared with spores from the individual host selection lines. Chemical spore analysis suggested that the spores from social selection lines escaped the caregivers' detection by containing lower levels of ergosterol, a key fungal membrane component. Experimental application of chemically pure ergosterol indeed induced sanitary grooming, supporting its role as a microbe-associated cue triggering host social immunity against fungal pathogens. By reducing this detection cue, pathogens were able to evade the otherwise very effective collective disease defences of their social hosts.

Immune function of the serosa in hemimetabolous insect eggs

Insects comprise more than a million species and many authors have attempted to explain this success by evolutionary innovations. A much overlooked evolutionary novelty of insects is the serosa, an extraembryonic epithelium around the yolk and embryo. We have shown previously that this epithelium provides innate immune protection to eggs of the beetle Tribolium castaneum. It remained elusive, however, whether this immune competence evolved in the Tribolium lineage or is ancestral to all insects. Here, we expand our studies to two hemimetabolous insects, the bug Oncopeltus fasciatus and the swarming grasshopper Locusta migratoria. For Oncopeltus, RNA sequencing reveals an extensive response upon infection, including the massive upregulation of antimicrobial peptides (AMPs). We demonstrate antimicrobial activity of these peptides using in vitro bacterial growth assays and describe two novel AMP families called Serosins and Ovicins. For both insects, quantitative polymerase chain reaction shows immune competence of the eggs when the serosa is present, and in situ hybridizations demonstrate that immune gene expression is localized in the serosa. This first evidence from hemimetabolous insect eggs suggests that immune competence is an ancestral property of the serosa. The evolutionary origin of the serosa with its immune function might have facilitated the spectacular radiation of the insects. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

Bioactivity Profiling of In Silico Predicted Linear Toxins from the Ants Myrmica rubra and Myrmica ruginodis

The venoms of ants (Formicidae) are a promising source of novel bioactive molecules with potential for clinical and agricultural applications. However, despite the rich diversity of ant species, only a fraction of this vast resource has been thoroughly examined in bioprospecting programs. Previous studies focusing on the venom of Central European ants (subfamily Myrmicinae) identified a number of short linear decapeptides and nonapeptides resembling antimicrobial peptides (AMPs). Here, we describe the in silico approach and bioactivity profiling of 10 novel AMP-like peptides from the fellow Central European myrmicine ants Myrmica rubra and Myrmica ruginodis. Using the sequences of known ant venom peptides as queries, we screened the venom gland transcriptomes of both species. We found transcripts of nine novel decapeptides and one novel nonapeptide. The corresponding peptides were synthesized for bioactivity profiling in a broad panel of assays consisting of tests for cytotoxicity as well as antiviral, insecticidal, and antimicrobial activity. U-MYRTX-Mrug5a showed moderately potent antimicrobial effects against several bacteria, including clinically relevant pathogens such as Listeria monocytogenes and Staphylococcus epidermidis, but high concentrations showed negligible cytotoxicity. U-MYRTX-Mrug5a is, therefore, a probable lead for the development of novel peptide-based antibiotics.

Fire ants feed their nestmates with their own venom

Venom secretion is widely used by ants for disease control and more generally as an external surface disinfectant. Here we report evidence that Solenopsis invicta feed their nestmates with their own venom. Venom alkaloids were found in crops and midguts of ants at concentration levels that have previously been reported as effective against various pathogens. These venom alkaloids were found in midguts of the larvae, indicating that trophallaxis must be involved in the transfer of venom, since larvae do not produce alkaloids and they depend on workers to be fed. After the mating flight, the female alates shed their wings, burrow into the soil, and start new colonies. The new queen provided alkaloids to her first batch of larvae in the new colony. Since the crops of female alates contain venom alkaloids donated from their nestmate workers, the transfer of worker alkaloids to new generation occurred. After minim adult workers emerged, they took the role in providing venom to the larvae in the colony. Minim adult workers eventually died out and the normal workers became the venom donors in the colony. Although other functions may be possible, considering the well-known antimicrobial property of venom alkaloids and their detected concentration levels, venom in the digestive system is most likely used as an internal antibiotic by fire ants.

Pathogen Prevalence Modulates Medication Behavior in Ant Formica fusca

Ants face unique challenges regarding pathogens, as the sociality which has allowed them to form large and complex colonies also raises the potential for transmission of disease within them. To cope with the threat of pathogens, ants have developed a variety of behavioral and physiological strategies. One of these strategies is self-medication, in which animals use biologically active compounds to combat pathogens in a way which would be harmful in the absence of infection. Formica fusca are the only ants that have previously been shown to successfully self-medicate against an active infection caused by a fungal pathogen by supplementing their diet with food containing hydrogen peroxide. Here, we build on that research by investigating how the prevalence of disease in colonies of F. fusca affects the strength of the self-medication response. We exposed either half of the workers of each colony or all of them to a fungal pathogen and offered them different combinations of diets. We see that workers of F. fusca engage in self-medication behavior even if exposed to a low lethal dose of a pathogen, and that the strength of that response is affected by the prevalence of the disease in the colonies. We also saw that the infection status of the individual foragers did not significantly affect their decision to forage on either control food or medicinal food as uninfected workers were also foraging on hydrogen peroxide food, which opens up the possibility of kin medication in partially infected colonies. Our results further affirm the ability of ants to self-medicate against fungal pathogens, shed new light on plasticity of self-medication and raise new questions to be investigated on the role self-medication has in social immunity.

Contrasting patterns of venom regeneration in a centipede (Scolopendra viridis) and a scorpion (Centruroides hentzi)

As biochemical traits with clear fitness consequences, venoms serve a critical ecological role for the animals that produce them. Understanding how venoms are maintained and regenerated after use will, therefore, provide valuable insight into the ecology of venomous animals. Furthermore, most studies on venomous organisms often require removing animals from the wild and waiting extended periods of time between venom extractions. Uncovering the patterns of venom regeneration across different species will likely lead to the development of more efficient venom extraction protocols, reducing both experimental time and the number of animals required. Using reversed-phase high-performance liquid chromatography, we identified asynchronous regeneration of venom protein component abundances in the centipede Scolopendra viridis but found no evidence for asynchronous venom regeneration in the scorpion Centruroides hentzi. We also observed high levels of intraspecific venom variation in C. hentzi, emphasizing the importance of testing for intraspecific venom variation in studies evaluating the synchronicity of venom regeneration. Although the regeneration of relative venom protein component abundances is an asynchronous process in S. viridis, we provide evidence that the presence-absence of major venom components is not an asynchronous process and suggest that studies relying on just the presence/absence of individual proteins (e.g. bioprospecting, drug discovery) could use catch-and-release methods of venom extraction to reduce the number of animals removed from the wild.

General Limitations to Endophytic Entomopathogenic Fungi Use as Plant Growth Promoters, Pests and Pathogens Biocontrol Agents

The multiple roles of fungal entomopathogens in host plants' growth promotion, pest and pathogen management have drawn huge attention for investigation. Endophytic species are known to influence various activities of their associated host plants, and the endophyte-colonized plants have been demonstrated to gain huge benefits from these symbiotic associations. The potential application of fungal endophytes as alternative to inorganic fertilizers for crop improvement has often been proposed. Similarly, various strains of insect pathogenic fungi have been formulated for use as mycopesticides and have been suggested as long-term replacement for the synthetic pesticides that are commonly in use. The numerous concerns about the negative effects of synthetic chemical pesticides have also driven attention towards developing eco-friendly pest management techniques. However, several factors have been underlined to be militating the successful adoption of entomopathogenic fungi and fungal endophytes as plant promoting, pests and diseases control bio-agents. The difficulties in isolation and characterization of novel strains, negative effects of geographical location, vegetation type and human disturbance on fungal entomopathogens, are among the numerous setbacks that have been documented. Although, the latest advances in biotechnology and microbial studies have provided means of overcoming many of these problems. For instance, studies have suggested measures for mitigating the negative effects of biotic and abiotic stressors on entomopathogenic fungi in inundative application on the field, or when applied in the form of fungal endophytes. In spite of these efforts, more studies are needed to be done to achieve the goal of improving the overall effectiveness and increase in the level of acceptance of entomopathogenic fungi and their products as an integral part of the integrated pest management programs, as well as potential adoption as an alternative to inorganic fertilizers and pesticides.

Social isolation causes downregulation of immune and stress response genes and behavioural changes in a social insect

Humans and other social mammals experience isolation from their group as stressful, triggering behavioural and physiological anomalies that reduce fitness. While social isolation has been intensely studied in social mammals, it is less clear how social insects, which evolved sociality independently, respond to isolation. Here we examined whether the typical mammalian responses to social isolation, e.g., an impaired ability to interact socially and immune suppression are also found in social insects. We studied the consequences of social isolation on behaviour and brain gene expression in the ant Temnothorax nylanderi. Following isolation, workers interacted moderately less with adult nestmates, increased the duration of brood contact, and reduced the time spent self-grooming, an important sanitary behaviour. Our brain transcriptome analysis revealed that only a few behaviour-related genes had altered their expression with isolation time. Rather, many genes linked to immune system functioning and stress response had been downregulated. This probably sensitizes isolated individuals to various stressors, in particular because isolated workers exhibit reduced sanitary behaviour. We provide evidence of the diverse consequences of social isolation in social insects, some of which resemble those found in social mammals, suggesting a general link between social well-being, stress tolerance, and immune competence in social animals.

Chance or Necessity-The Fungi Co-Occurring with Formica polyctena Ants

Simple Summary

There are about 13,800 species of ants living around the world, but only some of them have been extensively studied in the context of their non−antagonistic relationships with fungi. The best−known example is the symbiosis between leaf−cutting ants and fungi serving them as food. Others include the relationship between ants living in carton nests in the trees’ canopy with fungi increasing the durability of the nest. Do ants utilize fungi in the northern hemisphere and cooler climatic zone? This question is still open. Our goal was to study the less−obvious interactions between ants and common fungi in temperate climates. In our study, we characterized the mycobiota of the surroundings of Formica polyctena ants. We identified nearly 600 strains and investigated their taxonomic affinity. The most abundant fungi in F. polyctena nests are strains belonging to Penicillium—a genus well−known as an antibiotic producer. Other common and widespread fungi related to Penicillium, such as the toxin−producing Aspergillus species, were isolated very rarely. Additionally, the high diversity and high frequency of Penicillium colonies isolated from ants in this study suggest that certain representatives of this genus may be adapted to survive in ant nests, or that they are preferentially sustained by the insects.

Abstract

Studies on carton nesting ants and domatia−dwelling ants have shown that ant–fungi interactions may be much more common and widespread than previously thought. Until now, studies focused predominantly on parasitic and mutualistic fungi–ant interactions occurring mostly in the tropics, neglecting less−obvious interactions involving the fungi common in ants’ surroundings in temperate climates. In our study, we characterized the mycobiota of the surroundings of Formica polyctena ants by identifying nearly 600 fungal colonies that were isolated externally from the bodies of F. polyctena workers. The ants were collected from mounds found in northern and central Poland. Isolated fungi were assigned to 20 genera via molecular identification (ITS rDNA barcoding). Among these, Penicillium strains were the most frequent, belonging to eight different taxonomic sections. Other common and widespread members of Eurotiales, such as Aspergillus spp., were isolated very rarely. In our study, we managed to characterize the genera of fungi commonly present on F. polyctena workers. Our results suggest that Penicillium, Trichoderma, Mucor, Schwanniomyces and Entomortierella are commonly present in F. polyctena surroundings. Additionally, the high diversity and high frequency of Penicillium colonies isolated from ants in this study suggest that representatives of this genus may be adapted to survive in ant nests environment better than the other fungal groups, or that they are preferentially sustained by the insects in nests.

Behavioral Immunity and Social Distancing in the Wild: The Same as in Humans?

The COVID-19 pandemic imposed new norms on human interactions, perhaps best reflected in the widespread application of social distancing. But social distancing is not a human invention and has evolved independently in species as dissimilar as apes and lobsters. Epidemics are common in the wild, where their spread is enhanced by animal movement and sociality while curtailed by population fragmentation, host behavior, and the immune systems of hosts. In the present article, we explore the phenomenon of behavioral immunity in wild animals as compared with humans and its relevance to the control of disease in nature. We start by explaining the evolutionary benefits and risks of sociality, look at how pathogens have shaped animal evolution, and provide examples of pandemics in wild animal populations. Then we review the known occurrences of social distancing in wild animals, the cues used to enforce it, and its efficacy in controlling the spread of diseases in nature.

Immunotranscriptome analysis of Plutella xylostella reveals differences in innate immune responses to low- and high-virulence Beauveria bassiana strain challenges

BACKGROUND

Entomopathogenic fungi have developed multiple strategies to overcome the immune defenses of their target insects, whereas insect pests have devised various defense mechanisms to combat fungal infection. However, differences in the molecular mechanisms of the innate immune defense strategies of insects upon infection with different fungal strains from the same species have not been reported.

RESULTS

Two Beauveria bassiana strains were obtained that significantly varied in their pathogenicity but were comparable in terms of growth, conidial yield, and cuticle penetration. To investigate the molecular mechanisms underlying the immune response of Plutella xylostella infected with these two strains, RNA-Seq was performed 48 h after infection. A total of 1027 differentially expressed genes (DEGs) were identified, and more than 200 DEGs were enriched in Kyoto Encyclopedia of Genes and Genome (KEGG) pathways involved in disease response, revealing differences in the immune response of P. xylostella to different B. bassiana infections at 48 h. Twenty-eight of the DEGs were related to innate immune functions, such as pathogen recognition, immune system activation and antimicrobial reactions. RNA interference (RNAi)-mediated gene silencing assays showed that PxApoLIII and PxCSP played critical roles in the P. xylostella immune response. PxApoLIII was expressed at higher levels during infection with the high-virulence strain, whereas PxCSP showed the opposite expression pattern during infection with the low-virulence strain, indicating that PxApoLIII and PxCSP might participate in P. xylostella innate immune defense against high- and low-virulence B. bassiana strains.

CONCLUSION

The present findings demonstrate that strains of a single species of pathogenic fungi that differ in virulence can induce the expression of different genes in P. xylostella. These results advance our knowledge of the molecular mechanisms underlying fungi-pest interactions.

Preventing Transmission of Lethal Disease: Removal Behaviour of Lasius fuliginosus (Hymenoptera: Formicidae) Towards Fungus Contaminated Aphids

The ability of ants to detect and remove conidia-contaminated aphids, aimed at limiting contacts with potentially dangerous entities, is an effective antifungal mechanism to prevent the spread of infection among both their nestmates and aphids, their main suppliers of carbohydrates. However, the spread and the scale of this quarantining behaviour among ants are still scarcely studied. Among seven ant species studied, active usage of quarantining behaviour was found only in Formica ants. The behaviour of Lasius fuliginosus (Latreille) aphid milkers towards Chaitophorus populeti (Panzer) aphids covered with conidia of Beauveria bassiana (Balsamo-Crivelli) Vuillemin was studied in the field. Most aggressive milkers quickly detected and removed conidia-contaminated aphids from the plant, carrying them down and placing them some distance away from the experimental aspen trees. In general, active usage of quarantining behaviour towards conidia-contaminated aphids was found to be not limited to the genus Formica, but typical of L. fuliginosus as well. The response of milkers of L. fuliginosus and Formica s. str. ants to living aphids covered with conidia is quite similar. Removal of most fungus-contaminated aphids from the plant enables these ants to reduce the risk of infection transmission among both their nestmates and aphids.

Sickness and the Social Brain: Love in the Time of COVID

As a highly social species, inclusion in social networks and the presence of strong social bonds are critical to our health and well-being. Indeed, impaired social functioning is a component of numerous neuropsychiatric disorders including depression, anxiety, and substance use disorder. During the current COVID-19 pandemic, our social networks are at risk of fracture and many are vulnerable to the negative consequences of social isolation. Importantly, infection itself leads to changes in social behavior as a component of "sickness behavior." Furthermore, as in the case of COVID-19, males and females often differ in their immunological response to infection, and, therefore, in their susceptibility to negative outcomes. In this review, we discuss the many ways in which infection changes social behavior-sometimes to the benefit of the host, and in some instances for the sake of the pathogen-in species ranging from eusocial insects to humans. We also explore the neuroimmune mechanisms by which these changes in social behavior occur. Finally, we touch upon the ways in which the social environment (group living, social isolation, etc.) shapes the immune system and its ability to respond to challenge. Throughout we emphasize how males and females differ in their response to immune activation, both behaviorally and physiologically.

Bacterial exposure leads to variable mortality but not a measurable increase in surface antimicrobials across ant species

Social insects have co-existed with microbial species for millions of years and have evolved a diversity of collective defenses, including the use of antimicrobials. While many studies have revealed strategies that ants use against microbial entomopathogens, and several have shown ant-produced compounds inhibit environmental bacterial growth, few studies have tested whether exposure to environmental bacteria represents a health threat to ants. We compare four ant species’ responses to exposure to Escherichia coli and Staphylococcus epidermidis bacteria in order to broaden our understanding of microbial health-threats to ants and their ability to defend against them. In a first experiment, we measure worker mortality of Solenopsis invicta, Brachymyrmex chinensis, Aphaenogaster rudis, and Dorymyrmex bureni in response to exposure to E. coli and S. epidermidis. We found that exposure to E. coli was lethal for S. invicta and D. bureni, while all other effects of exposure were not different from experimental controls. In a second experiment, we compared the antimicrobial ability of surface extracts from bacteria-exposed and non-exposed S. invicta and B. chinensis worker ants, to see if exposure to E. coli or S. epidermidis led to an increase in antimicrobial compounds. We found no difference in the inhibitory effects from either treatment group in either species. Our results demonstrate the susceptibility to bacteria is varied across ant species. This variation may correlate with an ant species’ use of surface antimicrobials, as we found significant mortality effects in species which also were producing antimicrobials. Further exploration of a wide range of both bacteria and ant species is likely to reveal unique and nuanced antimicrobial strategies and deepen our understanding of how ant societies respond to microbial health threats.

Nest substrate, more than ant activity, drives fungal pathogen community dissimilarity in seed-dispersing ant nests

Myrmecochory is a widespread mutualism in which plants benefit from seed dispersal services by ants. Ants might also be providing seeds with an additional byproduct benefit via reduced plant pathogen loads in the ant nest environment through their antimicrobial glandular secretions. We investigate this byproduct benefit by identifying fungal communities in ant nests and surrounding environments and quantifying fungal community change (1) through time, (2) between different nest substrates, and (3) as a function of average ant activity levels within nests (based on observed ant activity at nest entrances throughout the summer). We split fungal communities by functional guild to determine seed-dispersing ant-induced changes in the overall fungal community, the animal pathogen fungal community, the plant pathogen fungal community, and the myrmecochore pathogen fungal community. Nest substrate (soil or log) explained much of the variation in fungal community dissimilarity, while substrate occupation (ant nest or control sample) and time had no influence on fungal community composition. Average ant activity had no effect on the community turnover in fungal communities except for the myrmecochore pathogenic fungal community. In this community, higher ant activity throughout the summer resulted in more fluctuation in the pathogenic community in the ant nest. Our results are not consistent with a byproduct benefit framework in myrmecochory, but suggest that nest substrate drives dissimilarity in fungal communities. The influence of nest substrate on fungal communities has important implications for seeds taken into ant nests, as well as ant nest location choice by queens and during nest relocation.

Formicine ants swallow their highly acidic poison for gut microbial selection and control

Animals continuously encounter microorganisms that are essential for health or cause disease. They are thus challenged to control harmful microbes while allowing the acquisition of beneficial microbes. This challenge is likely especially important for social insects with respect to microbes in food, as they often store food and exchange food among colony members. Here we show that formicine ants actively swallow their antimicrobial, highly acidic poison gland secretion. The ensuing acidic environment in the stomach, the crop, can limit the establishment of pathogenic and opportunistic microbes ingested with food and improve the survival of ants when faced with pathogen contaminated food. At the same time, crop acidity selectively allows acquisition and colonization by Acetobacteraceae, known bacterial gut associates of formicine ants. This suggests that swallowing of the poison in formicine ants acts as a microbial filter and that antimicrobials have a potentially widespread but so far underappreciated dual role in host-microbe interactions.

Behaviours indicating cannibalistic necrophagy in ants are modulated by the perception of pathogen infection level

Cannibalistic necrophagy is rarely observed in social hymenopterans, although a lack of food could easily favour such behaviour. One of the main supposed reasons for the rarity of necrophagy is that eating of nestmate corpses carries the risk of rapid spread of pathogens or parasites. Here we present an experimental laboratory study on behaviour indicating consumption of nestmate corpses in the ant Formica polyctena. We examined whether starvation and the fungal infection level of the corpses affects the occurrence of cannibalistic necrophagy. Our results showed that the ants distinguished between corpses of different types and with different levels of infection risk, adjusting their behaviour accordingly. The frequency of behaviours indicating cannibalistic necrophagy increased during starvation, although these behaviours seem to be fairly common in F. polyctena even in the presence of other food sources. The occurrence and significance of cannibalistic necrophagy deserve further research because, in addition to providing additional food, it may be part of the hygienic behaviour repertoire. The ability to detect infections and handle pathogens are important behavioural adaptations for social insects, crucial for the fitness of both individual workers and the entire colony.

Formic Acid as an Antimicrobial for Poultry Production: A Review

Organic acids continue to receive considerable attention as feed additives for animal production. Most of the emphasis to date has focused on food safety aspects, particularly on lowering the incidence of foodborne pathogens in poultry and other livestock. Several organic acids are currently either being examined or are already being implemented in commercial settings. Among the several organic acids that have been studied extensively, is formic acid. Formic acid has been added to poultry diets as a means to limit Salmonella spp. and other foodborne pathogens both in the feed and potentially in the gastrointestinal tract once consumed. As more becomes known about the efficacy and impact formic acid has on both the host and foodborne pathogens, it is clear that the presence of formic acid can trigger certain pathways in Salmonella spp. This response may become more complex when formic acid enters the gastrointestinal tract and interacts not only with Salmonella spp. that has colonized the gastrointestinal tract but the indigenous microbial community as well. This review will cover current findings and prospects for further research on the poultry microbiome and feeds treated with formic acid.

Prophylactic Avoidance of Hazardous Prey by the Ant Host Myrmica rubra

Ants are the hosts of many microorganisms, including pathogens that are incidentally brought inside the nest by foragers. This is particularly true for scavenging species, which collect hazardous food such as dead insects. Foragers limit sanitary risks by not retrieving highly infectious prey releasing entomopathogenic fungal spores. This study investigates whether similar prophylactic strategies are also developed for food associated with weak or delayed risks of fungal contamination. We compared, in Myrmica rubra ant colonies, the retrieval dynamics of dead flies that were (1) conidia-free, (2) covered with a low amount of Metarhizium brunneum entomopathogenic conidia or (3) recently fungus-killed but not yet sporulating. Foragers mostly avoided fungus-killed prey and delayed the retrieval of conidia-covered flies. A second sanitary filter occurred inside the nest through a careful inspection of the retrieved prey. Ultimately, ants mostly consumed conidia-free and conidia-covered flies, but they relocated and discarded all fungus-killed prey outside of the nest. Our study confirms that, as a host of generalist entomopathogenic fungi, Myrmica rubra ants have developed a prophylactic avoidance and a differential management of prey depending on their infectious potential. We discuss the functional value as well as the possible cues underlying pathogen avoidance and prey discrimination in ants.

Overlooked Scents: Chemical Profile of Soma, Volatile Emissions and Trails of the Green Tree Ant, Oecophylla smaragdina

The green tree ant, Oecophylla smaragdina, is one of only two recognized species of weaver ants. While the identity and functions of chemicals produced and emitted by its congener O. longinoda have been studied quite extensively and serve as a valuable model in chemical ecology research, little comparable information is available about O. smaragdina. Although some analyses of chemicals produced and emitted by O. smaragdina have been reported, the literature is fragmentary and incomplete for this species. To address this knowledge gap, and to enable comparisons in the chemical ecology of the two weaver ant species, we here describe diverse chemicals from the cuticle, Dufour's glands, poison glands, head, headspace volatiles, and trails of O. smaragdina.

Pathogen defence is a potential driver of social evolution in ambrosia beetles

Social immunity-the collective behavioural defences against pathogens-is considered a crucial evolutionary force for the maintenance of insect societies. It has been described and investigated primarily in eusocial insects, but its role in the evolutionary trajectory from parental care to eusociality is little understood. Here, we report on the existence, plasticity, effectiveness and consequences of social pathogen defence in experimental nests of cooperatively breeding ambrosia beetles. After an Aspergillus spore buffer solution or a control buffer solution had been injected in laboratory nests, totipotent adult female workers increased their activity and hygienic behaviours like allogrooming and cannibalism. Such social immune responses had not been described for a non-eusocial, cooperatively breeding insect before. Removal of beetles from Aspergillus-treated nests in a paired experimental design revealed that the hygienic behaviours of beetles significantly reduced pathogen prevalence in the nest. Furthermore, in response to pathogen injections, female helpers delayed dispersal and thus prolonged their cooperative phase within their mother's nest. Our findings of appropriate social responses to an experimental immune challenge in a cooperatively breeding beetle corroborate the view that social immunity is not an exclusive attribute of eusocial insects, but rather a concomitant and presumably important feature in the evolutionary transitions towards complex social organization.

Microbiota and the social brain

Sociability can facilitate mutually beneficial outcomes such as division of labor, cooperative care, and increased immunity, but sociability can also promote negative outcomes, including aggression and coercion. Accumulating evidence suggests that symbiotic microorganisms, specifically the microbiota that reside within the gastrointestinal system, may influence neurodevelopment and programming of social behaviors across diverse animal species. This relationship between host and microbes hints that host-microbiota interactions may have influenced the evolution of social behaviors. Indeed, the gastrointestinal microbiota is used by certain species as a means to facilitate communication among conspecifics. Further understanding of how microbiota influence the brain in nature may be helpful for elucidating the causal mechanisms underlying sociability and for generating new therapeutic strategies for social disorders in humans, such as autism spectrum disorders (ASDs).