Cuticular Profiles Research Articles

In vivo solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS) assay to identify epicuticular profiles across task groups of Apis mellifera ligustica workers

Colony integrity and survival in honeybees is regulated by chemical signals that are actively produced by glands and synergically transmitted between the members. A number of these signals regulate the typical age-related division of labor among the worker bees performing different tasks at different ages. In this study, the analysis of the cuticular profiles in Apis mellifera ligustica Spinola, 1806 workers at various tasks (newly emerged, nurse and forager bees) was performed using in vivo solid-phase microextraction gas chromatography-mass spectrometry (SPMEGC- MS). The use of in vivo SPME shed new light on the complexity of the molecular pattern on the epicuticle of honeybees. The identified molecules are mainly hydrocarbons, saturated and unsaturated carboxylic acids, and to a less extent, esters, sterols, aldehydes, and alcohols. Their relative abundance between the three task groups was evaluated using descriptive statistics and multivariate pattern recognition analysis (i.e., principal component analysis, PCA, and linear discriminant analysis, LDA). Eleven molecules namely nonacosane, pentacosane, (Z)-12-pentacosene, 11-tricosene, 11-methylnonacosane, squalene, 13-methylheptacosane, heptacosane, heneicosane, docosane and tricosane, occur with high frequency in newly emerged, nurse, and forager bees. The compounds that contributed the most for the separation of the three task groups in the PCA were pentacosane, (Z)-12-pentacosene, 13-methylheptacosane and squalene; while for LDA, nonacosane, 11-methylnonacosane and pentacosane were the molecules that contributed most to the discrimination.

Detection of very long-chain hydrocarbons by laser mass spectrometry reveals novel species-, sex-, and age-dependent differences in the cuticular profiles of three Nasonia species.

Long-chain cuticular hydrocarbons (CHC) are key components of chemical communication in many insects. The parasitoid jewel wasps from the genus Nasonia use their CHC profile as sex pheromone and for species recognition. The standard analytical tool to analyze CHC is gas chromatography coupled with mass spectrometric detection (GC/MS). This method reliably identifies short- to long-chain alkanes and alkenes, but CHC with more than 40 carbon atoms are usually not detected. Here, we applied two laser mass spectrometry (MS) techniques, namely direct laser desorption/ionization (d)LDI and silver-assisted (Ag-)LDI MS, respectively, to analyze CHC profiles of N. vitripennis, N. giraulti, and N. longicornis directly from the cuticle or extracts. Furthermore, we applied direct analysis in real-time (DART) MS as another orthogonal technique for extracts. The three methods corroborated previous results based on GC/MS, i.e., the production of CHC with carbon numbers between C25 and C40. However, we discovered a novel series of long-chain CHC ranging from C41 to C51/C52. Additionally, several previously unreported singly and doubly unsaturated alkenes in the C31-C39 range were found. Use of principal component analysis (PCA) revealed that the composition of the newly discovered CHC varies significantly between species, sex, and age of the animals. Our study adds to the growing literature on the presence of very long-chain CHC in insects and hints at putative roles in insect communication. Graphical abstract.

The possible role of ant larvae in the defence against social parasites.

Temporary social parasite ant queens initiate new colonies by entering colonies of host species, where they begin laying eggs. As the resident queen can be killed during this process, host colonies may lose their entire future reproductive output. Selection thus favours the evolution of defence mechanisms, before and after parasite intrusion. Most studies on social parasites focus on host worker discrimination of parasite queens and their offspring. However, ant larvae can also influence brood composition by consuming eggs. This raises the question whether host larvae can aid in preventing colony takeover by consuming eggs laid by parasite queens. To test whether larvae could play a role in anti-parasite defence, we compared the rates at which larvae of a common host species, Formica fusca, consumed eggs laid by social parasite, non-parasite, nest-mate, or conspecific non-nest-mate queens. Larvae consumed social parasite eggs more than eggs laid by a heterospecific non-parasite queen, irrespective of the chemical distance between the egg cuticular profiles. Also, larvae consumed eggs laid by conspecific non-nest-mate queens more than those laid by nest-mate queens. Our study suggests that larvae may act as players in colony defence against social parasitism, and that social parasitism is a key factor shaping discrimination behaviour in ants.

Irrigation affects characteristics of narrow-leaved lupin (Lupinus angustifolius L.) seeds

Main conclusionWhile plant irrigation usually increases yield, irrigation also affects seed characteristics with respect to endoreplication level, chemical composition, number of carbonyl bands, and cuticular wax profiles.Seeds of sweet varieties of the narrow-leaved lupin have good nutritional properties; however, these plants are sensitive to water deficit. Irrigation improves lupin yield, but can affect seed characteristics. The purpose of the study was to evaluate irrigation influence on lupin seed features and their chemical composition. Morphological analyses showed worse quality of seeds from the irrigated plants, with regard to their size and weight. This was confirmed by cytophotometric analyses which revealed a lower DNA content in the nuclei of cells from the apical and basal regions of the irrigated seeds. The lower degree of polyploidy of the nuclei entails lower cell sizes and limited space for storage components. Fourier transform infrared spectroscopic analysis demonstrated that protein and cuticular wax profiles of the irrigated seeds were different from the control. The electrophoretic analyses indicated differences in protein profiles including changes in the proportion of lupin storage proteins. Among the various studied elements, only the nitrogen content decreased in the embryo axis of irrigated plants. Although germination dynamics of the irrigated seeds was higher, the seedlings’ development rate was slightly lower than in the control. The hydrogen peroxide level in root meristem cells was higher during germination in the control suggesting its regulatory role in seed metabolism/signaling. Our study indicated that irrigation of lupin plant affected seed features and composition.

Chemical profiles in Iberoformica subrufa and Formica frontalis, a new example of temporary host–parasite interaction

The aim of this paper is to describe the relationship between two ant species, Formica frontalis and Iberoformica subrufa, found together in shared nests. Therefore, we obtained data from dug nests and outdoor activity in two sympatric populations and investigated the cuticular hydrocarbons (CHCs) in both sympatric populations and in 10 I. subrufa allopatric populations to unravel whether the relationship becomes tuned between both species. We also determined the CHCs of two sympatric Serviformica species (F. cunicularia and F. lemani). Our results showed that the ant F. frontalis is a temporary parasite of I. subrufa which facultatively forms mixed colonies complying with a loose form of the Emery’s rule. Alkanes and methylalkanes are the most abundant compounds found in F. frontalis and I. subrufa CHCs, respectively, but esters were only abundant in I. subrufa. As far as the CHC similarity is concerned, the sympatric free-living hosts were chemically closer to the parasite, albeit not identical, whereas the allopatric I. subrufa populations always maintained a separate CHC composition. We provide different potential hypotheses to explain this similarity of cuticular profiles only in the two geographically distant sympatric populations.

Prudent behavior rather than chemical deception enables a parasite to exploit its ant host

Many parasites display complex strategies to evade host detection. The principal view is that the parasites of social insects deceive their host by means of advanced chemical adaptations such as mimicking the cuticular host recognition cues, being chemically odorless, or emitting manipulative volatiles. Apart from these chemical adaptations, parasites of social insects may also use simpler behavioral strategies to evade host detection. As yet, such a behavior has rarely been studied. Here we tested which chemical and behavioral strategies the unspecialized parasitic rove beetle Thiasophila angulata uses to avoid detection by its aggressive Formica rufa red wood ant host. Chemical comparisons of the beetle's and the host ants' cuticular hydrocarbons showed that the beetle carried an idiosyncratic cuticular profile that was clearly different from that of its host. Beetles that were isolated from their host or were placed in the nests of another Formica species perfectly retained their original cuticular profiles and provoked equal levels of aggression. These results suggest that the beetles do not avoid host detection through chemical deception. In contrast, the beetle adapted its behavior to avoid aggression by the ants. In the presence of ants, the beetle behaved much more prudently by hiding more frequently and engaging in less risky runs. Overall, these results highlight that for relatively unspecialized parasites, general strategies such as prudent behavior can be equally effective as more specialized deception strategies to evade host detection.

An uneasy alliance: a nesting association between aggressive ants and equally fierce social wasps.

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder, its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta (F.). In French Guiana, 83.33% of the 48 P. rejecta nests recorded were found side by side with those of A. chartifex. This nesting association results in mutual protection from predators (i.e., the wasps protected from army ants; the ants protected from birds). We conducted field studies, laboratory-based behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association. Due to differences in the cuticular profiles of the two species, we eliminated the possibility of chemical mimicry. Also, analyses of the carton nests did not reveal traces of marking on the envelopes. Because ant forager flows were not perturbed by extracts from the wasps' Dufour's and venom glands, we rejected any hypothetical action of repulsive chemicals. Nevertheless, we noted that the wasps "scraped" the surface of the upper part of their nest envelope using their mandibles, likely removing the ants' scent trails, and an experiment showed that ant foragers were perturbed by the removal of their scent trails. This leads us to use the term "erasure hypothesis." Thus, this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to "contain" their associated ants through the elimination of their scent trails, direct attacks, "wing-buzzing" behavior and ejecting the ants.

Life history and chemical ecology of the Warrior wasp Synoeca septentrionalis (Hymenoptera: Vespidae, Epiponini).

Swarm-founding ‘Warrior wasps’ (Synoeca spp.) are found throughout the tropical regions of South America, are much feared due to their aggressive nest defence and painful sting. There are only five species of Synoeca, all construct distinctive nests that consist of a single sessile comb built onto the surface of a tree or rock face, which is covered by a ribbed envelope. Although locally common, research into this group is just starting. We studied eight colonies of Synoeca septentrionalis, a species recently been described from Brazil. A new colony is established by a swarm of 52 to 140 adults that constructs a colony containing around 200 brood cells. The largest colony collected containing 865 adults and over 1400 cells. The number of queen’s present among the eight colonies varied between 3 and 58 and no clear association between colony development and queen number was detected. Workers and queens were morphologically indistinguishably, but differences in their cuticular hydrocarbons were detected, particularly in their (Z)-9-alkenes. The simple cuticular profile, multiple queens, large size and small number of species makes the ‘Warrior wasps’ an excellent model group for further chemical ecology studies of swarm-founding wasps.

A mimetic nesting association between a timid social wasp and an aggressive arboreal ant

In French Guiana, the arboreal nests of the swarm-founding social wasp Protopolybia emortualis (Polistinae) are generally found near those of the arboreal dolichoderine ant Dolichoderus bidens. These wasp nests are typically protected by an envelope, which in turn is covered by an additional carton ‘shelter’ with structure resembling the D. bidens nests. A few wasps constantly guard their nest to keep D. bidens workers from approaching. When alarmed by a strong disturbance, the ants invade the host tree foliage whereas the wasps retreat into their nest. Notably, there is no chemical convergence in the cuticular profiles of the wasps and ants sharing a tree. The aggressiveness of D. bidens likely protects the wasps from army ant raids, but the ants do not benefit from the presence of the wasps; therefore, this relationship corresponds to a kind of commensalism.

Beetles “in red”: are the endangered flat bark beetles Cucujus cinnaberinus and C. haematodes chemically protected? (Coleoptera: Cucujidae)

Two native species of the genus Cucujus show a wide geographic distribution in Europe, Cucujus cinnaberinus (Scopoli, 1763) and C. haematodes Erichson, 1845. Although data on the distribution and ecology of these rare and endangered species are increasing, there are few reports on their biology and behaviour, and some aspects of their feeding ecology remain problematic. Our aim was to study, for the first time, the cuticular chemical profiles of these two beetles to (i) investigate the presence of chemicals potentially involved in defence by pathogens and (ii) lay the foundation for understanding the role of their bright red colour. The analysis of the cuticular profile was performed in-vivo by solid phase microextraction coupled with gas chromatography-mass spectrometry. In the cuticular profiles of the two species we identified 24 compounds belonging to different classes of molecules, i.e. hydrocarbons, aldehydes, esters, n-alkyl morpholines, and a high number of organic acids. Qualitative differences in terms of both signal intensity and detected compounds were found between the two species. As reported in other insects, the remarkable array of avoidance substances suggests a strict relationship with the bright red colour of the adults, which probably acts as an aposematic or warning signal. European Cucujus species are probably well protected against enemies because some identified chemicals, particularly fatty acids, are related to an anti-predatory strategy to fight off predators that use their sense of smell to locate their prey. Other substances found on the cuticular layer of these beetles are probably involved in an antimicrobial and antifungal function, as demonstrated in other insects living in habitats that host many pathogens.

Intraspecific Variation of the Composition of Linear Alkanes in Social Wasp Mischocyttarus consimilis

An important attribute of the evolution and maintenance of sociality in insects is their ability to distinguish members of their own colonies by means of chemical signals during their interactions. Of this type of signals, the cuticular hydrocarbons, responsible among other functions, for intraspecific recognition stand out. Linear alkanes are indicated as the class of compounds that would be most involved in water retention in the body of insects, however, some studies have investigated their role as mediators of interactions. Thus it is possible that there is significant intraspecific variation of its composition, so the objective of this study was to test the hypothesis that linear alkanes vary significantly among populations, castes and sexes, as well as between newly emerged females of different ages of the Mischocyttarus consimilis Zikán 1949 wasp. The samples were analyzed by gas chromatography with flame ionization detector and gas chromatography coupled to mass spectrometry. The results show that there is a significant variation between the chemical cuticular profiles of samples from different populations, as well as between castes, sex and newly emergent workers of different ages. Therefore, it is possible to infer that this class of compounds may vary according to genetic differences between populations, but also by different environmental conditions. The differences between castes, sex and ages suggest that these compounds may also be involved in mediating interactions between nestmates.

Testing the role of cuticular hydrocarbons on intercolonial agonism in two subterranean termite species (Coptotermes) and their hybrids

Recognition of nestmates is an important function in many social insects, as it maintains colony integrity by preventing outsiders from entering the colony. Agonism usually results from the interaction of con-specific non-nestmate individuals in termite colonies. Previous studies hypothesized that the cuticular hydrocarbon (CHC) profile of individuals had a role in nestmate recognition. However, contradictory results from previous studies in some subterranean termites raise questions on the validity of the cuticular hydrocarbon hypothesis. In the current study, Coptotermes gestroi (Wasmann), Coptotermes formosanus Shiraki and their hybrids were reared in identical conditions from colony foundation. This approach eliminates sources of variability in their cuticular hydrocarbon profiles aside from a genetic component. The parental species displayed dissimilar profiles of predominant alkanes and methyl alkanes, but both hybrid types displayed an overlapping, intermediate profile of these CHC. The mixture of the most abundant CHCs alone did not determine kin recognition; while the two hybrid types’ CHC profiles converged, the hybrids still showed strong agonism. One of the hybrid mating types easily merged with C. formosanus, despite only partial genetic similarity and dissimilar cuticular profiles for the common alkanes and methyl alkanes. This study suggests that in Coptotermes termites, the variable abundance of the major alkanes and methyl alkanes commonly found in most Coptotermes species does not explain agonistic patterns, and that other factors such as possibly more complex but less abundant CHC are likely to be involved in colonial recognition.

Do Distinct Biomes Influence the Cuticular Chemical Profile in Orchid Bees?

Cuticular chemical profiles of Euglossa cordata L. males were analyzed to test whether ecological predictors affect their composition and relative proportion. Males were collected in areas of Caatinga and Atlantic Forest from Brazil during two distinct seasonal periods. We found 48 compounds from the cuticular extracts of males, which consisted of hydrocarbons (71.39%), acetates (16.79%), esters (10.5%), alcohols and others (1.31%). We verified that when specimens were separated between biomes, they did not show a qualitative differentiation, but a small quantitative variation of compounds was found between some alkanes. We suggest that these results reflect stability of epicuticular compounds even under variable environmental conditions.

Caste discrimination in the ant Odontomachus hastatus: What role for behavioral and chemical cues?

In social insects, the maintenance of genetic colony integrity requires resident workers to recognize any intruder with a reproductive potential and to behave appropriately to minimize fitness costs. In this study, our objective was to identify the relative contribution of the behavioral patterns and chemical cues of intruders with different fertility status on their likelihood of being accepted in monogynous colonies. Using the ponerine ant Odontomachus hastatus as a model organism, we introduced non-nestmate workers, founding queens and heterospecific workers on intact nests in the field. We demonstrated that resident workers were more aggressive toward founding queens than toward non-nestmates workers originating from the same or a distant population. Lab experiments showed that the patterns of aggression did not differ substantially between chilled and live ants, which suggests that chemical cues alone allow caste discrimination. However, the absence of behavioral cues produced more variable results in the outcome of interactions. We also showed that resident workers readily accepted non-nestmate mature queens. The analysis of cuticular profiles revealed that individuals belonging to different castes and fertility status have contrasted chemical signatures. Overall, our study revealed that workers exhibit a graded behavioral response depending on the reproductive status of intruders. We discussed the observed variation in the extent of aggression in relation to the potential fitness costs associated with acceptance or rejection error of individuals differing in fertility status.

Mutations at the Darkener of Apricot locus modulate pheromone production and sex behavior in Drosophila melanogaster

Mutations at the Darkener of Apricot (Doa) locus of Drosophila melanogaster alter sexual differentiation by disrupting sex-specific splicing of doublesex pre-mRNA, a key regulator of sex determination. Here, we study the effect of seven Doa alleles and several trans-heterozygous combinations on pheromones and courtship behavior. The cuticular hydrocarbon (CHC) profile was slightly masculinized in females, with an accumulation of shorter compounds (C23 and C25) and a reduction in longer compounds (C27 and C29). The profile was feminized in males. Female cuticular profiles showed fewer dienes and female pheromones in six alleles and in the trans-heterozygotes and showed more male pheromones (tricosene and pentacosene) in three alleles (DEM, E786 and HD) and in all trans-heterozygotes.Courtship was severely affected in Doa males; in particular, males made fewer copulation attempts and copulated less with both control and Doa females.These results suggest that Doa could modulate pheromone production and sex behavior by altering sexual differentiation in the cuticle and the nervous system.

Bee guards detect foreign foragers with cuticular chemical profiles altered by phoretic varroa mites

Detection of diseased individuals in a social group is a critical step of social immunity, to prevent the spread of parasites or pathogens. Parasite-induced alterations of the host phenotype might be used by healthy conspecific to identify an individual bearing a threat to the social group, and to prevent it from entering the colony. The ecto-parasitic varroa mite (Varroa destructor) is a crucial driver for the extensive worldwide honey bee losses, and the parasite is currently considered one of the major threats for apiculture. Here, we first investigated the alterations induced by phoretic varroa mites on the cuticular hydrocarbons profile of adult honey bees. Our gas chromatography–mass spectrometry analyses showed an increase in cuticular methyl-branched compounds of parasitized bees. Then, we used lure presentation experiments to evaluate the response of guard honey bees at the hive entrance towards foreign foragers with a parasite-altered cuticular profile. We found an increase in the aggressive responses of guard bees towards bee-lures with a parasite-altered cuticular profile, highlighting the ability of Apis mellifera guard bees to recognize the alterations induced by varroa in the cuticular profile of alien bees.

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

BackgroundCockroaches 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.ResultsWe 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.ConclusionsNest-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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0089-5) contains supplementary material, which is available to authorized users.

Cannibalism in spiderlings is not only about starvation

Many species show a transient group life, and dispersal often coincides with the onset of agonistic behaviors. Changes in the nature of interactions among conspecifics can rely on a variation in the production of communication cues and/or on a switch in the processing of social information. The relative contribution of each process on the initiation of aggression still remains to be investigated. Spiders constitute relevant models to address this issue since all solitary species undergo a transient gregarious phase prior dispersal. In this study, we developed a combination of behavioral and physiological assays to examine the mechanisms accompanying the onset of agonistic interactions in spiderlings of the solitary species Agelena labyrinthica. Juveniles of different developmental stages were supplied with diets differing in prey availability. We showed that unfed spiderlings never molted, retained their cuticular lipid signature, and did not behave aggressively. This contrasted with fed individuals that molted, changed their cuticular profiles, and displayed agonistic interactions and cannibalism. We demonstrated that depletion in lipid stores was not sufficient to elicit aggression or cannibalism. Our analysis also revealed that major shifts in cuticular profiles only occurred after the first molt outside the cocoon. The lack of agonistic interactions in unfed spiderlings suggests an absence of behavioral plasticity in response to food shortage at the earliest developmental stages. We propose that the initiation of aggression relies more on a shift in the production of cuticular cues accompanying molting rather than on changes in information processing depending on the physiological state of individuals. Most species of spiders display a transient gregarious phase preceding the initiation of agonistic interactions and dispersal. We examined what factors are associated with the onset of aggression in gregarious juveniles and we showed that pre-dispersing spiderlings despite low energetic stores never cannibalized conspecifics. This contrasts with later instars that displayed increased levels of aggression. The initiation of agonistic interactions coincided with major changes in the profiles of cuticular lipids, which are used in spiders to regulate social interactions. Our study suggests that depletion of lipid stores is not sufficient to trigger aggression but that it likely requires changes in communication cues associated with molting. We propose that the absence of behavioral plasticity of pre-dispersing juveniles in response to starvation allows spiderlings to maintain social cohesion and to benefit from the potential advantages granted by gregariousness, irrespective of environmental fluctuations.

Does larval food affect cuticular profiles and recognition in eusocial bees? a test on Scaptotrigona gynes (Hymenoptera: Meliponini)

The relative contributions of heritable and environmentally acquired components of colony odor towards individual recognition are scarcely known in social insects. Larval food may affect cuticular profiles which in turn may serve as cues in the process of elimination of excess gynes characteristic of the eusocial stingless bees. In this study, we evaluated the contribution of larval food to cuticular profiles of stingless bee gynes and quantitatively tested if recognition (latency) from workers may be related to gyne chemotype and origin in the species Scaptotrigona pectoralis. Our results showed that the origin of food did not significantly affect the cuticular profiles of gynes, as larvae of the same origin reared on food from different colonies showed similar cuticular profiles at emergence. We suggest that overlapping over floral resources may account for the similarity in cuticular cues derived from food across experimental colonies. Additionally, workers showed similar latency time to first aggression towards gynes irrespectively of their chemotype and origin. Gyne’s mass had no effect on the aggressive response from workers either. We observed that gynes threatened aggressive workers which counteracted further aggression. Our results indicate that in stingless bees, cuticular hydrocarbons at emergence seem to have genetic origin and that gyne tolerance seems not related to cuticular chemical profiles. We suggest that cuticular cues may serve as caste labels for the identification of newly emerged gynes after which worker aggression towards them would elicit behavioral indicators of their fitness. We studied the effect of larval food on the cuticular profile of stingless bee gynes coupled with an evaluation of the effect of chemotype in gyne recognition by workers in Scaptotrigona. We used artificial methods of gyne rearing that avoid nest odor acquisition of newly emerged individuals so that the effect of food could be better analyzed on gynes reared on food of their own colony and a different one. The origin of larval food did not significantly affect the cuticular profiles of gynes and workers attacked gynes irrespective of their chemotype. Our results demonstrate that cuticular chemical profiles are explained by genetic origin and not larval diet and that workers’ aggressive responses to gynes are independent of gyne colony origin.

Nestmate larval discrimination by workers in the swarm-founding wasp Polybia paulista

The discrimination of nestmates is an important requisite to avoid exploitation by unrelated individuals. Although recognition among adult social wasps has been examined in detail, few studies have investigated brood discrimination by adults. Adult females of some Polistes species were previously shown to discriminate their nestmate larvae on the basis of cuticular hydrocarbons. However, nestmate larval discrimination has not been studied in polygynous swarm-founding wasps of the tribe Epiponini. Whether the workers of Polybia paulista recognised their own larvae when presented outside the nest comb was investigated in the present study. We also compared the cuticular chemical profiles of 5th instar larvae from different colonies. Workers did not bite non-nestmate larvae more frequently than their nestmate larvae. However, they spent significantly more time licking with their nestmate larvae than with non-nestmate larvae. These behavioural tests suggest that the workers of P. paulista may have the ability to distinguish between larvae from their own colony and alien larvae. The epicuticle of larvae had 69 compounds consisting of linear and methyl branched compounds with chains from 19 to 36 carbon atoms. Analyses of the cuticular extracts of 5th instar larvae from the experimental colonies significantly allocated (100%) in their predicted groups, suggesting that discrimination of own larvae by the workers may be mediated by colony-specific, larval-borne cues. These results suggest that workers of the swarm-founding wasp P. paulista recognised the larvae of their own nest from alien larvae according to distinct cuticular chemical profiles. Because it is not so far known that swarm-founding wasps exhibit intraspecific colony usurpation, this discrimination is not used in their colonial life even if workers recognise the chemical cues between more or less related larvae. Our results also imply that nestmate larval recognition could be evolved in colonies with many matrilines, as P. paulista colonies have.