Using wasps as a tool to restore a functioning vine grape mycobiota and preserve the mycobial "terroir".

In the last one-hundred years, the exponential expansion of wine making has artificialized the agricultural landscape as well as its microbial diversity, spreading human selected Saccharomyces cerevisiae strains. Evidence showed that social wasps can harbor a significant fraction of the yeast phenotypic diversity of a given area of wine production, allowing different strains to overwinter and mate in their gut. The integrity of the wasp-yeast ecological interaction is of paramount importance to maintain the resilience of microbial populations associated to wine aromatic profiles. In a field experiment, we verified whether Polistes dominula wasps, reared in laboratory and fed with a traceable S. cerevisiae strain, could be a useful tool to drive the controlled yeast dispersion directly on grapes. The demonstration of the biotechnological potential of social insects in organic wine farming lays the foundations for multiple applications including maintenance of microbial biodiversity and rewilding vineyards through the introduction of wasp associated microbiomes.

Mutualistic Relationships between Microorganisms and Eusocial Wasps (Hymenoptera, Vespidae).

Eusocial wasps are represented in the Vespidae by the subfamilies Stenogastrinae, Vespinae and Polistinae. These wasps present colonies that are sometimes composed of thousands of individuals which live in nests built with paper materials. The high density of the adult and larval population, as well as the stable micro environment of the nests, make very favourable conditions for the flourishing of various types of microorganisms. These microorganisms, which may be pathogens, are beneficial and certainly contribute to model the sociality of these insects. The mutualistic relationships that we observe in some species, especially in Actinomycete bacteria and yeasts, could have important fallouts for the development of new medicines and for the use of these insects in agricultural environments.

Venom Collection by Electrical Stimulation in the Invasive Species Polistes dominula Reared Using a Vespiculture Regime.

Specific Venom Immunotherapy (VIT) is practiced with venom extracted from insects, and is the specific therapy used for patients highly allergic to social insect (Hymenoptera) stings. Due to the dramatic shortage of vespid species in the local environment, we coupled vespiculture techniques of Polistes paper wasps with a venom collection procedure based on the electrical stimulation of individuals from entire colonies. The procedure involves little to no disturbance of the individual insects, and at the same time, successfully allows for the extraction of venom containing all allergens necessary for VIT.

Effect of climate on strategies of nest and body temperature regulation in paper wasps, Polistes biglumis and Polistes gallicus.

Polistes paper wasps are a widespread taxon inhabiting various climates. They build nests in the open without a protective outer layer, which makes them vulnerable to changing temperatures. To better understand the options they have to react to environmental variation and climate change, we here compare the thermoregulatory behavior of Polistes biglumis from cool Alpine climate with Polistes gallicus from warm Mediterranean climate. Behavioral plasticity helps both of them to withstand environmental variation. P. biglumis builds the nests oriented toward east-south-east to gain solar heat of the morning sun. This increases the brood temperature considerably above the ambience, which speeds up brood development. P. gallicus, by contrast, mostly avoids nesting sites with direct insolation, which protects their brood from heat stress on hot days. To keep the brood temperature below 40-42 °C on warm days, the adults of the two species show differential use of their common cooling behaviors. While P. biglumis prefers fanning of cool ambient air onto the nest heated by the sun and additionally cools with water drops, P. gallicus prefers cooling with water drops because fanning of warm ambient air onto a warm nest would not cool it, and restricts fanning to nests heated by the sun.

Antifungals, arthropods and antifungal resistance prevention: lessons from ecological interactions.

Arthropods can produce a wide range of antifungal compounds, including specialist proteins, cuticular products, venoms and haemolymphs. In spite of this, many arthropod taxa, particularly eusocial insects, make use of additional antifungal compounds derived from their mutualistic association with microbes. Because multiple taxa have evolved such mutualisms, it must be assumed that, under certain ecological circumstances, natural selection has favoured them over those relying upon endogenous antifungal compound production. Further, such associations have been shown to persist versus specific pathogenic fungal antagonists for more than 50 million years, suggesting that compounds employed have retained efficacy in spite of the pathogens' capacity to develop resistance. We provide a brief overview of antifungal compounds in the arthropods' armoury, proposing a conceptual model to suggest why their use remains so successful. Fundamental concepts embedded within such a model may suggest strategies by which to reduce the rise of antifungal resistance within the clinical milieu.

Increased immunocompetence and network centrality of allogroomer workers suggest a link between individual and social immunity in honeybees.

The significant risk of disease transmission has selected for effective immune-defense strategies in insect societies. Division of labour, with individuals specialized in immunity-related tasks, strongly contributes to prevent the spread of diseases. A trade-off, however, may exist between phenotypic specialization to increase task efficiency and maintenance of plasticity to cope with variable colony demands. We investigated the extent of phenotypic specialization associated with a specific task by using allogrooming in the honeybee, Apis mellifera, where worker behaviour might lower ectoparasites load. We adopted an integrated approach to characterize the behavioural and physiological phenotype of allogroomers, by analyzing their behavior (both at individual and social network level), their immunocompetence (bacterial clearance tests) and their chemosensory specialization (proteomics of olfactory organs). We found that allogroomers have higher immune capacity compared to control bees, while they do not differ in chemosensory proteomic profiles. Behaviourally, they do not show differences in the tasks performed (other than allogrooming), while they clearly differ in connectivity within the colonial social network, having a higher centrality than control bees. This demonstrates the presence of an immune-specific physiological and social behavioural specialization in individuals involved in a social immunity related task, thus linking individual to social immunity, and it shows how phenotypes may be specialized in the task performed while maintaining an overall plasticity.

No evidence of queen immunisation despite transgenerational immunisation in Crematogaster scutellaris ants.

Like vertebrates, invertebrates evolved acquired immunity based on memory-like mechanisms, known as immunisation. Immunisation and its transmission among individuals are phylogenetically ancestral and conserved characters that have been reported in different insect orders. Physiological mechanisms are still largely unknown, and the high variability in responses in different host-parasite systems led to different conclusions. In social insect species, the complex organisation of colonies further complicates the interpretation of the immune responses. In ants, it has been shown that the expression of immunisation depends on species, caste and physiological status of individuals. In this study, we investigate the occurrence of immunisation in queens of Crematogaster scutellaris ants using the fungus Metarhizium anisopliae as elicitor. Foundation in C. scutellaris is claustral and monogynic, allowing us to test the existence of the phenomenon in two distinct physiological conditions, corresponding to the claustral and colonial phases of queens. Queens and foundresses challenged with heavy doses of the pathogen showed higher mortality if previously exposed to light doses, indicating the absence of immunisation in our experimental settings. On the other hand, evidence of the trans-generational immunisation in the same host-parasite system has been recently found, where workers produced by queens exposed to light doses of M. anisopliae survived longer than those belonging to the control group. These results indicate that foundresses exposed to M. anisopliae can elicit an increased resistance in the offspring without providing themselves with a similar increased immune response and that immunisation and trans-generational immunisation are uncoupled phenomena in this host-parasite system.

Saccharomyces cerevisiae Induces Immune Enhancing and Shapes Gut Microbiota in Social Wasps.

Trained immunity is the enhanced response of the innate immune system to a secondary infection after an initial encounter with a microorganism. This non-specific response to reinfection is a primitive form of adaptation that has been shown to be conserved from plants to mammals. Insects lack an acquired immune component and rely solely on an innate one, and they have expanded it upon traits of plasticity and adaptation against pathogens in the form of immune priming. The recent discoveries of the role of Saccharomyces cerevisiae in the insect's ecology and the ability of this yeast to induce trained immunity in different organisms suggest that insects could have developed mechanisms of adaptation and immune enhancing. Here, we report that two yeast strains of S. cerevisiae, previously shown to induce trained immunity in mammals, enhance resistance to Escherichia coli infection in the paper wasp Polistes dominula. The reduction of injected E. coli load by S. cerevisiae strains was statistically significant in future foundresses but not in workers, and this occurs before and after hibernation. We thus investigated if the effect on E. coli was mirrored by variation in the gut microbiota composition. Foundresses, showing immune enhancing, had statistically significant changes in composition and diversity of gut bacterial communities but not in the fungal communities. Our results demonstrate that S. cerevisiae can prime insect responses against bacterial infections, providing an advantage to future foundress wasps to carry these microorganisms. Understanding the mechanisms involved in the generation of specific and long-lasting immune response against pathogenic infections in insects and the influence of the induction of trained immunity on the commensal gut microbiota could have a major impact on modern immunology.

Home economics in an oak gall: behavioural and chemical immune strategies against a fungal pathogen in Temnothorax ant nests.

Nest architecture is a fundamental character shaping immune strategies of social insects. The arboreal ant Temnothorax unifasciatus nests in cavities such as oak galls where the entire colony lives in a unique small chamber. In these conditions, physiological and behavioural strategies likely prevail over compartmentalisation and are presumably tuned with colony size. We designed two experiments to study chemical and behavioural immune strategies against the entomopathogenic fungus Metarhizium anisopliae in colonies of different sizes. First, we compared spore germination and length of germinal tubes inside artificial nests, designed to impede the contact between the ants and the fungus, in colonies of different size. In the absence of direct contact, Temnothorax unifasciatus colonies inhibit fungal growth inside their nests, presumably through volatile compounds. The analysis revealed a positive correlation between fungistatic activity and colony size, indicating that workers of smaller colonies do not invest a higher per capita effort in producing such substances compared to larger colonies. Second, we performed a removal experiment of contaminated and non-contaminated items introduced inside the nests of colonies of different size. Small colonies challenged with contaminated fibres showed an increased removal of all the items (both contaminated and non-contaminated) compared to small colonies challenged with non-contaminated fibres only. Conversely, larger colonies moved items regardless of the presence of the spores inside the nest. Colony size qualitatively affected removal of waste items showing a pathogen elicited reaction in small colonies to optimise the reduced workforce, while the removal behaviour in larger colonies revealed to be expressed constitutively.

Natural biocide disrupts nestmate recognition in honeybees.

Honeybee colonies are under the threat of many stressors, biotic and abiotic factors that strongly affect their survival. Recently, great attention has been directed at chemical pesticides, including their effects at sub-lethal doses on bee behaviour and colony success; whereas the potential side effects of natural biocides largely used in agriculture, such as entomopathogenic fungi, have received only marginal attention. Here, we report the impact of the fungus Beauveria bassiana on honeybee nestmate recognition ability, a crucial feature at the basis of colony integrity. We performed both behavioural assays by recording bee guards' response towards foragers (nestmate or non-nestmate) either exposed to B. bassiana or unexposed presented at the hive entrance, and GC-MS analyses of the cuticular hydrocarbons (CHCs) of fungus-exposed versus unexposed bees. Our results demonstrated that exposed bees have altered cuticular hydrocarbons and are more easily accepted into foreign colonies than controls. Since CHCs are the main recognition cues in social insects, changes in their composition appear to affect nestmate recognition ability at the colony level. The acceptance of chemically unrecognizable fungus-exposed foragers could therefore favour forager drift and disease spread across colonies.

Antennal Protein Profile in Honeybees: Caste and Task Matter More Than Age.

Reproductive and task partitioning in large colonies of social insects suggest that colony members belonging to different castes or performing different tasks during their life (polyethism) may produce specific semiochemicals and be differently sensitive to the variety of pheromones involved in intraspecific chemical communication. The main peripheral olfactory organs are the antennal chemosensilla, where the early olfactory processes take place. At this stage, members of two different families of soluble chemosensory proteins [odorant-binding proteins (OBPs) and chemosensory proteins (CSPs)] show a remarkable affinity for different odorants and act as carriers while a further family, the Niemann-Pick type C2 proteins (NPC2) may have a similar function, although this has not been fully demonstrated. Sensillar lymph also contains Odorant degrading enzymes (ODEs) which are involved in inactivation through degradation of the chemical signals, once the message is conveyed. Despite their importance in chemical communication, little is known about how proteins involved in peripheral olfaction and, more generally antennal proteins, differ in honeybees of different caste, task and age. Here, we investigate for the first time, using a shotgun proteomic approach, the antennal profile of honeybees of different castes (queens and workers) and workers performing different tasks (nurses, guards, and foragers) by controlling for the potential confounding effect of age. Regarding olfactory proteins, major differences were observed between queens and workers, some of which were found to be more abundant in queens (OBP3, OBP18, and NPC2-1) and others to be more abundant in workers (OBP15, OBP21, CSP1, and CSP3); while between workers performing different tasks, OBP14 was more abundant in nurses with respect to guards and foragers. Apart from proteins involved in olfaction, we have found that the antennal proteomes are mainly characterized by castes and tasks, while age has no effect on antennal protein profile. Among the main differences, the strong decrease in vitellogenins found in guards and foragers is not associated with age.

Chemical Communication and Reproduction Partitioning in Social Wasps.

Social wasps encompass species displaying diverse social organization regarding colony cycle, nest foundation, caste differences (from none to significant dimorphism) and number of reproductive queens. Current phylogenetic data suggests that sociality occured independently in the subfamily Stenogastrinae and in the Polistinae+Vespinae clade. In most species, including those with the simplest social organization, colony reproduction is monopolised by a single or few females. Since their nest mates can also develop ovaries and lay eggs, dominant females must somehow inhibit them from reproducing. Physical interactions in the form of open aggression or, usually, ritualised dominance by the fertile females contribute to fertility inhibition in several species, but it is unlikely to function in large colonies. In the latter case, reproduction within the colony is likely to be regulated through pheromones. Relatively little is known about these semiochemicals. Studies on all the three social wasp subfamilies, revealed that cuticular hydrocarbon components differ in abundance between egg-laying and not egg-laying females and that their composition depends on fertility status. In several species, females have been reported to manifestly react towards females with activated ovaries, but there is little evidence to support the hypothesis that fertile individuals are either recognized through their CHC composition, or that over-represented CHC constituents can inhibit fertility. Moreover, very little information exists on the possibility that exocrine glands release fertility signals or chemicals inhibiting fertility.

Trans-generational immunization in the acrobat ant Crematogaster scutellaris.

Trans-generational immunization is defined as the transmission of an enhanced resistance to a pathogen from parents to offspring. By using the host-parasite system of the ant Crematogaster scutellaris and the entomopathogenic fungus Metarhizium anisopliae, we describe this phenomenon for the first time in ants. We exposed four groups of hibernating queens to different treatments (i) a non-lethal dose of live conidiospores in Triton, (ii) a dose of heat-killed conidiospores in Triton, (iii) a control Triton solution, and (iv) a naive control. We exposed their first workers to a high dose of conidiospores and measured mortality rates. Workers produced by queens exposed to live conidiospores survived longer than those belonging to the other groups, while exposure to Triton and dead spores had no effect. Starved workers showed a significantly higher mortality. The treatments did not influence queen mortality, nor the number of offspring they produced at the emergence of the first worker, showing no evidence of immunization costs-at least for these parameters in the first year of colony development. We propose that trans-generational immunization represents an important component of social immunity that could affect colony success, particularly during the critical phase of claustral foundation.

Climate changes and Hymenoptera venom allergy: are there some connections?

PURPOSE OF REVIEW: This review aims to update the world status of the main allergenic stinging Hymenoptera. RECENT FINDINGS: In this review, we consider the problems that social Hymenoptera (bees, wasps and ants) could represent in the nearest future for human health in different parts of the world. SUMMARY: Distribution and consistency of allergenic species including venomous insects are interested by accelerated dynamics caused by climate changes and globalization. Owing to the expansion of ranges of native species and colonization of invasive ones, even in the uncertainty of present available models, new challenges presented by stinging Hymenoptera should be expected in the future.

Facial patterns in a tropical social wasp correlate with colony membership.

Social insects excel in discriminating nestmates from intruders, typically relying on colony odours. Remarkably, some wasp species achieve such discrimination using visual information. However, while it is universally accepted that odours mediate a group level recognition, the ability to recognise colony members visually has been considered possible only via individual recognition by which wasps discriminate 'friends' and 'foes'. Using geometric morphometric analysis, which is a technique based on a rigorous statistical theory of shape allowing quantitative multivariate analyses on structure shapes, we first quantified facial marking variation of Liostenogaster flavolineata wasps. We then compared this facial variation with that of chemical profiles (generated by cuticular hydrocarbons) within and between colonies. Principal component analysis and discriminant analysis applied to sets of variables containing pure shape information showed that despite appreciable intra-colony variation, the faces of females belonging to the same colony resemble one another more than those of outsiders. This colony-specific variation in facial patterns was on a par with that observed for odours. While the occurrence of face discrimination at the colony level remains to be tested by behavioural experiments, overall our results suggest that, in this species, wasp faces display adequate information that might be potentially perceived and used by wasps for colony level recognition.

Chemical disguise of myrmecophilous cockroaches and its implications for understanding nestmate recognition mechanisms in leaf-cutting ants.

BACKGROUND: Cockroaches of the genus Attaphila regularly occur in leaf-cutting ant colonies. The ants farm a fungus that the cockroaches also appear to feed on. Cockroaches disperse between colonies horizontally (via foraging trails) and vertically (attached to queens on their mating flights). We analysed the chemical strategies used by the cockroaches to integrate into colonies of Atta colombica and Acromyrmex octospinosus. Analysing cockroaches from nests of two host species further allowed us to test the hypothesis that nestmate recognition is based on an asymmetric mechanism. Specifically, we test the U-present nestmate recognition model, which assumes that detection of undesirable cues (non-nestmate specific substances) leads to strong rejection of the cue-bearers, while absence of desirable cues (nestmate-specific substances) does not necessarily trigger aggression. RESULTS: We found that nests of Atta and Acromyrmex contained cockroaches of two different and not yet described Attaphila species. The cockroaches share the cuticular chemical substances of their specific host species and copy their host nest's colony-specific cuticular profile. Indeed, the cockroaches are accepted by nestmate but attacked by non-nestmate ant workers. Cockroaches from Acromyrmex colonies bear a lower concentration of cuticular substances and are less likely to be attacked by non-nestmate ants than cockroaches from Atta colonies. CONCLUSIONS: Nest-specific recognition of Attaphila cockroaches by host workers in combination with nest-specific cuticular chemical profiles suggest that the cockroaches mimic their host's recognition labels, either by synthesizing nest-specific substances or by substance transfer from ants. Our finding that the cockroach species with lower concentration of cuticular substances receives less aggression by both host species fully supports the U-present nestmate recognition model. Leaf-cutting ant nestmate recognition is thus asymmetric, responding more strongly to differences than to similarities.

Ontogenic Caste Differences in the Van der Vecht Organ of Primitively Eusocial Neotropical Paper Wasps.

Recent studies have reported incipient morphological caste dimorphism in the Van der Vecht organ size of some temperate Polistes paper wasps. Whether species other than the temperate ones show a similar pattern remains elusive. Here, we have studied some Neotropical Polistes species. By comparing females collected through the year, we showed caste related differences in the size of the Van der Vecht organ in P. ferreri (body size corrected Van der Vech organ size of queens = 0.45 ± 0.06, workers = 0.38 ± 0.07 mm2, p = 0.0021), P. versicolor (body size corrected Van der Vech organ size of queens = 0.54 ± 0.11, workers = 0.46 ± 0.09 mm2, p = 0.010), but not P. simillimus (body size corrected Van der Vech organ size of queens = 0.52 ± 0.05, workers = 0.49 ± 0.06 mm2, p = 0.238). Therefore, it seems that queens and workers of some Neotropical Polistes have diverged in their ontogenic trajectory of the Van der Vecht organ size, providing clear evidence for incipient morphological caste dimorphism. As Polistes are distributed mostly in the tropics, we propose that physical caste differences may be widespread in the genus. Also, we highlight that morphological divergence in the queen-worker phenotypes may have started through differential selection of body structures, like the Van der Vecht organ.

Social wasp intestines host the local phenotypic variability of Saccharomyces cerevisiae strains.

Nowadays, the presence of Saccharomyces cerevisiae has been assessed in both wild and human-related environments. Social wasps have been shown to maintain and vector S. cerevisiae among different environments. The availability of strains isolated from wasp intestines represents a striking opportunity to assess whether the strains found in wasp intestines are characterized by peculiar traits. We analysed strains isolated from the intestines of social wasps and compared them with strains isolated from other sources, all collected in a restricted geographic area. We evaluated the production of volatile metabolites during grape must fermentation, the resistance to different stresses and the ability to exploit various carbon sources. Wasp strains, in addition to representing a wide range of S. cerevisiae genotypes, also represent large part of the phenotypes characterizing the sympatric set of yeast strains; their higher production of acetic acid and ethyl acetate could reflect improved ability to attract insects. Our findings suggest that the relationship between yeasts and wasps should be preserved, to safeguard not only the natural variance of this microorganism but also the interests of wine-makers, who could take advantage from the exploitation of their phenotypic variability. Copyright © 2016 John Wiley & Sons, Ltd.

Social wasps are a Saccharomyces mating nest.

The reproductive ecology of Saccharomyces cerevisiae is still largely unknown. Recent evidence of interspecific hybridization, high levels of strain heterozygosity, and prion transmission suggest that outbreeding occurs frequently in yeasts. Nevertheless, the place where yeasts mate and recombine in the wild has not been identified. We found that the intestine of social wasps hosts highly outbred S. cerevisiae strains as well as a rare S. cerevisiae×S. paradoxus hybrid. We show that the intestine of Polistes dominula social wasps favors the mating of S. cerevisiae strains among themselves and with S. paradoxus cells by providing a succession of environmental conditions prompting cell sporulation and spores germination. In addition, we prove that heterospecific mating is the only option for European S. paradoxus strains to survive in the gut. Taken together, these findings unveil the best hidden secret of yeast ecology, introducing the insect gut as an environmental alcove in which crosses occur, maintaining and generating the diversity of the ascomycetes.

The Rules of Aggression: How Genetic, Chemical and Spatial Factors Affect Intercolony Fights in a Dominant Species, the Mediterranean Acrobat Ant Crematogaster scutellaris.

Nest-mate recognition plays a key role in the biology of ants. Although individuals coming from a foreign nest are, in most cases, promptly rejected, the degree of aggressiveness towards non nest-mates may be highly variable among species and relies on genetic, chemical and environmental factors. We analyzed intraspecific relationships among neighboring colonies of the dominant Mediterranean acrobat ant Crematogaster scutellaris integrating genetic, chemical and behavioral analyses. Colony structure, parental relationships between nests, cuticular hydrocarbons profiles (CHCs) and aggressive behavior against non nest-mates were studied in 34 nests located in olive tree trunks. Bayesian clustering analysis of allelic variation at nine species-specific microsatellite DNA markers pooled nests into 14 distinct clusters, each representing a single colony, confirming a polydomous arrangement of nests in this species. A marked genetic separation among colonies was also detected, probably due to long distance dispersion of queens and males during nuptial flights. CHCs profiles varied significantly among colonies and between nests of the same colony. No relationship between CHCs profiles and genetic distances was detected. The level of aggressiveness between colonies was inversely related to chemical and spatial distance, suggesting a 'nasty neighbor' effect. Our findings also suggest that CHCs profiles in C. scutellaris may be linked to external environmental factors rather than genetic relationships.