Medium molecular weight polar substances of the cuticle as tools in the study of the taxonomy, systematics and chemical ecology of tropical hover wasps (Hymenoptera: Stenogastrinae)

Intraspecific Cuticular Chemical Profile Variation in the Social Wasp Mischocyttarus consimilis (Hymenoptera, Vespidae)

Chemical compounds present on the cuticle of social insects are important in communication, as they are used in recognition of nestmates and sexual partners as well as in caste distinction, varying according to several factors, such as genetic and environmental. In this context, some studies have explored the cuticular chemical profile as a tool for assessing intra- and interspecific differences in social insects, although few studies have investigated this in social wasps. This study aimed to assess the differences in cuticular chemical profiles among different geographic samples of the wasp Mischocyttarus consimilis Zikán. Our hypothesis was that environmental factors are decisive to compose the cuticular chemical profiles of colonies of these social wasps and that there are differences regarding the geographic distribution among colonies. We used Fourier Transform Infrared-Photoacoustic Spectroscopy (FTIR-PAS) to assess the chemical profiles of samples. Our results show that despite there are differences between the cuticular chemical composition of the wasps' samples from different populations, there is no significant correlation compared to the spatial distribution of the colonies nor with the environment. Thus, our hypothesis was refuted, and we can infer that in this species neither exogenous nor genetic factors stand out to differentiate the chemical signature of their colonies, but a combination of both.

Chemosystematics Using Cuticular Compounds: A Powerful Tool to Separate Species in Mediterranean Dung Beetles (Coleoptera: Geotrupidae)

The use of chemical characters to infer a phylogeny is known to be promising to ascertain phylogenetic relationships in controversial groups. Dung beetle classifications containing the Geotrupidae family, based on morphological characters and genes, are debated with respect to the subfamilies, such as the Bolboceratids. In our study, we used different approaches to generate and compare the Geotrupidae phylogenies based on genetics and chemotaxonomy. Cuticular compounds were analyzed for 12 species of Mediterranean dung beetles to build a chemical phylogeny. In addition, mitochondrial and nuclear marker concatenation have been used to elaborate the molecular phylogeny. Using the cuticular compound continuous data, our results showed that each species was associated with a specific chemical pattern and that all individuals belonging to the same species displayed a similar chemical blend. The most distant species was Bolbelasmus gallicus, with an evident distinction from the other species due to several compounds. The maximum parsimony tree showed that all genera belonging to a Geotrupidae subfamily were grouped in the same clade, with B. gallicus species isolated in another clade, similar to the chemotaxonomy grouping. A strong positive correlation between chemotaxonomy and genetic phylogeny has been demonstrated, underlying a genetic basis for cuticular hydrocarbon variations. Our results are congruent with previous studies using morphological or genetic data. Our results also showed that only 10 compounds can be used to distinguish at least six species of dung beetle and that chemotaxonomy could become a useful and affordable tool to determine phylogenetic relationships in insects.

Comparison and correlation between chemical profiles of cephalic salivary glands and cuticle surface of workers ofApis mellifera(Hymenoptera, Apidae)

The cuticle surface of insects displays functions in communication, such as recognition. It is known that oenocytes are responsible for the origin of the compounds found in the epicuticle. Secretion of exocrine glands might be added to the original composition during the insect’s life. The aims of the present study were (i) to quantify and to qualify the chemical compounds in cephalic salivary glands (CSG) and cuticle surface of workers of Apis mellifera L., 1758; (ii) to compare chemical profiles of both gland and cuticle; (iii) to verify if the epicuticular and CSG profile compositions allow separation of the workers into phase-related groups. Glands and wings of newly emerged workers, nurses, and foragers were analyzed by gas chromatography – mass spectrometry. The results have shown that the main compounds in both were hydrocarbons. The Mantel correspondence analysis showed that there was relatively strong correspondence between CSG and cuticular surface in all groups, mainly nurses and foragers. From a total of 37 detected compounds, 29 were the same in both compartments. The results indicated that the gland secretion might be used to replenish the cuticular compounds. In conclusion, glands and cuticle profiles were phase-related and the CSG may be a potential auxiliary source of cuticular hydrocarbon replenishment in the studied species.

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.

Delineating species boundaries using an iterative taxonomic approach: the case of soldierless termites (Isoptera, Termitidae, Apicotermitinae)

Species boundaries are traditionally inferred using morphological characters, although morphology sometimes fails to correctly delineate species. To overcome this limitation, researchers have widely taken advantage of alternative methods such as DNA barcoding or analysis of cuticular hydrocarbons (CHs) profiles, but rarely use them simultaneously in an iterative taxonomic approach. Here, we follow such an approach using morphology, DNA barcoding and CHs profiles to precisely discriminate species of soldierless termites, a diversified clade constituting about one-third of the Neotropical termite species richness, but poorly resolved taxonomically due to the paucity of useful characters. We sampled soldierless termites in various forest types of the Nouragues Nature Reserve, French Guiana. Our results show that morphological species determination generally matches DNA barcoding, which only suggests the existence of three cryptic species in the 31 morphological species. Among them, Longustitermes manni is the only species whose splitting is corroborated by ecological data, other widely distributed species being supported by DNA barcoding. On the contrary, although CHs profiles provide a certain taxonomic signal, they often suggest inconsistent groupings which are not supported by other methods. Overall, our data support DNA barcoding and morphology as two efficient methods to distinguish soldierless termite species.

Major changes in the sex differences in cuticular chemical profiles of the western conifer seed bug (Leptoglossus occidentalis) after laboratory rearing

Chemical compounds covering the insect cuticle have several functions ranging from protection against water loss to inter- and intra-specific communication. Their composition is determined by several intrinsic and extrinsic factors. Among these factors, laboratory rearing has been poorly investigated even though it has a strong potential for biasing behavioral experiments. We selected an invasive species with unknown cuticular mixtures as a model. Our aim was to describe its mixtures and to determine if highly simplified laboratory rearing conditions interact with sexual signatures. We analyzed the cuticle by means of two different techniques - gas chromatography/mass spectrometry (GC/MS) and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) - to obtain data on a wide range of compounds with different molecular weight. We found that both sets of chemicals showed correlations with gender but also that cuticular waxes detected by GC/MS were highly dependent on rearing conditions, with a strong bias in sexual dimorphism. Conversely, the heavier signatures detected by MALDI-TOF showed a less clear diversification between sexes, although the discrimination power was unaffected by rearing conditions. The biological and practical implications of our findings are discussed.

From individual to collective immunity: the role of the venom as antimicrobial agent in the Stenogastrinae wasp societies

Sociality is associated with an increased risk of disease transmission and one of the first defense of the insect colonies is represented by antimicrobial secretions. In many eusocial hymenopteran species venom glands represent one of the most important source of antimicrobial substances. It is known that in highly eusocial species the venom is spread on both the cuticle of insects and the comb, thus becoming a component of the so called "social immunity". So far, it is never been ascertained whether this phenomenon is also present in more primitively eusocial and incipiently eusocial groups. Using incipiently eusocial hover wasps as model, we demonstrate that venom is present on insect cuticles and that it strongly acts against microorganisms. By contrast, the nest, regardless of materials, does not represent a ''medium" where the venom is deposited by wasps in order to act as a social antiseptic weapon. Our findings discussed in an evolutionary perspective indicate that a certain degree of sociality or a sufficient number of individuals in an insect society are thresholds to be reached for the rise of complex and efficient forms of collective and social immunity as mechanisms of resistance to diseases.

Cuticular compounds bring new insight in the post-glacial recolonization of a Pyrenean area: Deutonura deficiens Deharveng, 1979 complex, a case study

Background

In most Arthropod groups, the study of systematics and evolution rely mostly on neutral characters, in this context cuticular compounds, as non-neutral characters, represent an underexplored but potentially informative type of characters at the infraspecific level as they have been routinely proven to be involved in sexual attraction.

Methods and Findings

The collembolan species complex Deutonura deficiens was chosen as a model in order to test the utility of these characters for delineating four infraspecific entities of this group. Specimens were collected for three subspecies (D. d. deficiens, D. d. meridionalis, D. d. sylvatica) and two morphotypes (D. d. sylvatica morphoype A and B) of the complex; an additional species D. monticola was added. Cuticular compounds were extracted and separated by gas chromatography for each individual. Our results demonstrate that cuticular compounds succeeded in separating the different elements of this complex. Those data allowed also the reconstruction of the phylogenetic relationships among them.

Conclusions

The discriminating power of cuticular compounds is directly related to their involvement in sexual attraction and mate recognition. These findings allowed a discussion on the potential involvement of intrinsic and paleoclimatic factors in the origin and the diversification of this complex in the Pyrenean zone. This character type brings the first advance from pattern to process concerning the origin of this species complex.

Differences in venom and cuticular peptides in individuals of Apis mellifera (Hymenoptera: Apidae) determined by MALDI-TOF MS

The fraction between 950 and 4000Da of the venom of Apis mellifera has been analyzed with MALDI-TOF mass spectrometry and statistical facilities of the ClinProTools software. Consistent differences in the composition of this venom fraction were observed between queens and workers while younger and older workers (nurses and guards as well as foragers) differ for the relative percentages of two well known cytolytic peptides, namely Melittin and Apamin. Total in situ body methanol extracts and methanol micro-extractions on the cuticle of various parts of the body of drones and females confirmed that venom peptides are smeared on the body surface of females in a not yet clarified way. The observation that venom peptides have been found also on comb wax rises the hypothesis that the use of venom as antimicrobial agent makes part of the social immunity system of A. mellifera.