Cuticular Profiles Research Articles

Structure and ultrastructure of the silk glands and spinneret of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

This study provides comprehensive documentation of silk production in the pest moth Helicoverpa armigera from gland secretion to extrusion of silk thread. The structure of the silk glands, accessory structures and extrusion apparatus are reported. The general schema of the paired silk glands follows that found for Lepidoptera. Morphology of the duct, silk press, muscle attachments and spigot are presented as a three-dimensional reconstruction and the cuticular crescent-shaped profile of the silk press is demonstrated in both open and closed forms with attendant muscle blocks, allowing advances in our knowledge of how the silk press functions to regulate the extrusion of silk. Growth of the spigot across instars is documented showing a distinctive developmental pattern for this extrusion device. Its shape and structure are related to use and load-bearing activity.

Wax combs mediate nestmate recognition by guard honeybees

Research has shown that the wax combs are important in the acquisition of colony odour in the honeybee, Apis mellifera. However, many of these studies were conducted in the laboratory or under artificial conditions. We investigated the role of the wax combs in nestmate recognition in the natural context of bees at colony entrances. Wax combs constructed by each experimental colony were swapped between hives and the acceptance of nestmate and non-nestmate forager workers was recorded before and after the swap, and in relation to a control hive not involved in the swap. We conducted the experiment twice, in consecutive years with three different colonies each time. Colonies that exchanged combs became more accepting of each other's workers than of workers from the third colony. The overall acceptance of comb swap non-nestmates increased significantly from 3% before the swap to 23% after the swap in the first year, and from 8 to 47% in the second year. This effect wore off within 3 weeks. Chemical analyses showed that the cuticular profile of non-nestmates involved in the experimental comb swap became more similar to each other after the swap, and that acceptance by guards of bees from different hives was negatively correlated with chemical distance between the hydrocarbon profiles of the workers from different hives.

Queen fertility, egg marking and colony size in the ant Camponotus floridanus

In ant societies, workers do not usually reproduce but gain indirect fitness benefits from raising related offspring produced by the queen. One of the preconditions of this worker self-restraint is sufficient fertility of the queen. The queen is, therefore, expected to signal her fertility. In Camponotus floridanus, workers can recognize the presence of a highly fertile queen via her eggs, which are marked with the queen's specific hydrocarbon profile. If information on fertility is encoded in the hydrocarbon profile of eggs, we expect workers to be able to differentiate between eggs from highly and weakly fertile queens. We found that workers discriminate between these eggs solely on the basis of their hydrocarbon profiles which differ both qualitatively and quantitatively. This pattern is further supported by the similarity of the egg profiles of workers and weakly fertile queens and the similar treatment of both kinds of eggs. Profiles of queen eggs correspond to the cuticular hydrocarbon profiles of the respective queens. Changes in the cuticular profiles are associated with the size of the colony the queen originates from and her current egg-laying rate. However, partial correlation analysis indicates that only colony size predicts the cuticular profile. Colony size is a buffered indicator of queen fertility as it is a consequence of queen productivity within a certain period of time, whereas daily egg-laying rate varies due to cyclical oviposition. We conclude that surface hydrocarbons of eggs and the cuticular profiles of queens both signal queen fertility, suggesting a major role of fertility signals in the regulation of reproduction in social insects.

Nestmate Recognition Cues in the Honey Bee: Differential Importance of Cuticular Alkanes and Alkenes

In social insects, recognition of nestmates from aliens is based on olfactory cues, and many studies have demonstrated that such cues are contained within the lipid layer covering the insect cuticle. These lipids are usually a complex mixture of tens of compounds in which aliphatic hydrocarbons are generally the major components. The experiments described here tested whether artificial changes in the cuticular profile through supplementation of naturally occurring alkanes and alkenes in honeybees affect the behaviour of nestmate guards. Compounds were applied to live foragers in microgram quantities and the bees returned to their hive entrance where the behaviour of the guard bees was observed. In this fashion we compared the effect of single alkenes with that of single alkanes; the effect of mixtures of alkenes versus that of mixtures of alkanes and the whole alkane fraction separated from the cuticular lipids versus the alkene fraction. With only one exception (the comparison between n-C(19) and (Z)9-C(19)), in all the experiments bees treated with alkenes were attacked more intensively than bees treated with alkanes. This leads us to conclude that modification of the natural chemical profile with the two different classes of compounds has a different effect on acceptance and suggests that this may correspond to a differential importance in the recognition signature.

A chemical level in the coevolutionary arms race between an ant social parasite and its hosts

Here we investigate the coevolutionary interactions between the slavemaking ant Protomognathus americanus and its Temnothorax hosts on a chemical level. We show that, although this social parasite is principally well-adapted to its hosts' cuticular hydrocarbon profile, there are pronounced differences in the fine-tuning of this adaptation. Between populations, chemical adaptation varies with host community composition, as the parasite faces a trade-off when confronted with more than one host species. In addition to adaptation of its own chemical signature, the slavemaker causes a reciprocal adjustment in its slaves' cuticular profile, the degree of which depends on the slave species. On the host side, successful parasite defence requires efficient enemy recognition, and in behavioural aggression trials, host colonies could indeed discriminate between invading slaves, which commonly accompany slavemakers on raids, and free-living conspecifics. Furthermore, hosts shifted their acceptance threshold over the seasons, presumably to reduce the costs of defence.

Epicuticular lipids and fertility in primitively social wasps (Hymenoptera Stenogastrinae)

Abstract. Lipid cuticular profiles of females of four species belonging to three different genera of stenogastrine wasps are examined in connection with reproductive potential (relative ovarian development). Cuticular lipids may not only represent the cues for nestmate discrimination (already behaviourally ascertained in three of the same species), but also allow discrimination of fertile and non fertile individuals. Comparisons with more socially evolved insects are reported and discussed.

Cuticular Hydrocarbons of Polistes dominulus as a Biogeographic Tool: A Study of Populations from the Tuscan Archipelago and Surrounding Areas

In social insects, the types and proportions of epicuticular lipids may exhibit significant diversity as a result of factors such as age, sex, caste, rank, nest, and relatedness. It is known that these variations can be used by social insects to acquire information regarding conspecific individuals. Recent findings have shown that different populations of Polistes dominulus (Christ.) have distinctly different chemical cuticular profiles, and that wasps are able to recognize individuals of their own population. In this study, we showed that cuticular hydrocarbon patterns of Polistes dominulus are consistent with similarities among northern Tyrrhenian islands, as reported in previous biogeographic studies. Indeed, our findings indicate that cuticular hydrocarbon mixtures of P. dominulus from Capraia and Corsica are grouped together by cluster analysis, while those from Elba and Giglio cluster with cuticular profiles of the mainland wasps (Venturina).

Reproductive monopoly enforced by sterile police workers in a queenless ant

In societies of totipotent insects, dyadic dominance interactions generate a hierarchy that often underlies an extreme reproductive skew. Subordinates remain infertile but can maximize their indirect fitness benefits through collective power (worker policing): interference with challenging high-rankers can prevent an untimely replacement of the reproductive. However, police workers only benefit if they favor individuals with high fertility. In the monogynous queenless ant Streblognathus peetersi, we used behavioral, physiological, and chemical methods to show that police workers have the primary role in the selection of the reproductive, and that they probably use reliable information about fertility encoded in the cuticular hydrocarbons to make their decision. We successfully decreased an alpha’s fertility by using a hormonal treatment (Pyriproxyfen, a juvenile hormone analogue), and she was always removed from the hierarchy by police workers. In the preceding days, one of the high-rankers became aggressive, although her interactions were not directed at the treated alpha. All treated alphas (n ¼ 10) remained aggressive but ended up immobilized by low-ranking workers after a median time of 11.5 days. By then, the challenging high ranker exhibited dominance behaviors typical of the alpha rank. In parallel, the cuticular profile of the treated alpha exhibited predictable and opposite modifications to that of the challenger’s. This is the first study that uncouples dominance and fertility in a social insect: it gives a better understanding of the crucial role of sterile helpers in the control of reproductive skew in animal societies. Key words: cuticular hydrocarbons, fertility signal, gamergate, juvenile hormone, Ponerinae, reproductive skew, worker policing. [Behav Ecol 15:970–975 (2004)]

Fertility signalling and reproductive skew in queenless ants

Social insects often show an extreme reproductive skew. In queenless ants, colonies consist of morphologically identical workers that can all potentially reproduce sexually. Similarly to that in social vertebrates, aggression in these ants functions to select the reproductive(s). We investigated the mechanisms underlying reproductive skew in the monogynous queenless ant Streblognathus peetersi . Behavioural observations of disturbed hierarchies were integrated with physiological measures of fertility (vitellogenin titre in the haemolymph) and chemical analysis of cuticular hydrocarbons, which are putative fertility pheromones. This multifaceted approach revealed that the colony reproductive is determined as a result of aggression between high-ranking workers, but once an alpha is established, chemical signalling is enough to maintain reproductive skew. As already reported in several species of ants and also in a social wasp, egg layers have distinct profiles of cuticular hydrocarbons compared with infertile workers. Importantly, ‘high rankers’ who are unable to lay eggs also have a specific cuticular profile; this is consistent with their intermediate state of fertility indicated by vitellogenin levels. Rather than just ovarian activity, the cuticular hydrocarbon profile thus reveals the individual hormonal state that underlies reproductive activity. We compare the fertility signal in queenless ants with the ‘badge of status’ reported in various birds. We discuss the evolutionary stability of this communication system and give special emphasis to ecological constraints and the high degree of intracolonial relatedness typical of social insects.

Rank integration in dominance hierarchies of host colonies by the paper wasp social parasite Polistes sulcifer (Hymenoptera, Vespidae)

In multiple-foundress nests of the wasp Polistes dominulus, dominance hierarchies are established among foundresses, and only the dominant (=alpha) individual lays eggs. The alpha female can be distinguished from subordinate females and workers on the basis of the proportions of some hydrocarbons present on the cuticle, suggesting that chemical signaling of her reproductive status could occur. P. dominulus is also the host species of the obligate social parasite Polistes sulcifer. After aggressively usurping host colonies and behaviorally replacing the host alpha female, parasites are characterized by a change in the proportions of their cuticular hydrocarbons to match that of the host cuticular profile at both species and colony levels. In the current study, we demonstrate that P. sulcifer queens also modify their cuticular hydrocarbon proportions after usurpation to match that of the host alpha female. Parasite females, therefore, acquire the dominant rank in host colonies both reproductively and chemically by mimicking the typical alpha profile of the host. Parasite females were not able to fully inhibit ovary development in host foundresses, and 10 days after usurpation, parasites, alpha and beta foundresses show similar chemical profiles and ovarian development.

Deciphering the recognition signature within the cuticular chemical profile of paper wasps

In social insects the mixture of cuticular hydrocarbons is generally considered to act as a recognition pheromone. However, little information exists on the relative importance of single compounds or of different classes of hydrocarbons. We tested the importance for nestmate recognition of a series of alkenes, methyl-branched alkanes and linear alkanes present in the cuticular profile of the social wasp Polistes dominulus. We applied the hydrocarbons on to live wasps and observed the behaviour of nestmates once the treated individual attempted to enter the nest. Linear alkanes had no effect upon the recognition response, whereas wasps treated with methyl-branched alkanes or alkenes were attacked. This is the first systematic evaluation of the role of hydrocarbon classes as recognition cues and begins to define the recognition signature within the cuticular profile for a genus regarded as a model organism for the study of recognition in animals.

Variations in chemical mimicry by the ectoparasitic mite Varroa jacobsoni according to the developmental stage of the host honey-bee Apis mellifera

The ectoparasitic mite Varroa jacobsoni poses a major threat to the survival of European honey-bee populations. Development of effective control methods is therefore much needed. Study of interspecific chemical communication between the parasite and host is a particularly promising avenue of research. Previous study has shown that the cuticular hydrocarbons of the parasite mite Varroa jacobsoni are qualitatively identical to those of its honey-bee host Apis mellifera (Nation J.L., Sanford M.T., Milne K., 1992. Cuticular hydrocarbons from Varroa jacobsoni. Experimental and Applied Acarology 16, 331–344). The purpose of the present study was to compare the cuticular hydrocarbon patterns of the two species at different stages of bee development. Cuticular components were identified by gas chromatography/mass spectrometry. The proportion of each component was calculated at three stages of bee development (larvae, pupa, emerging bee). The degree of chemical mimicry between the parasite and host was evaluated by multivariate analyses using the resulting proportions for each category of individuals. There were four main findings. The first was that the proportions of some components are different at the larval, pupal and imago stage of bee development. Second, Varroa profiles vary depending on the developmental stage of the host. Third, the cuticular profile of adult mites is more similar to that of the stage of the host than that of later and/or earlier stages except for parasites collected from emerging adult bees. Fourth, the degree of mimicry by Varroa is greater during larval and pupal stages than during the emerging adult bee stages. The role of chemical mimicry — although it is not perfect — in enabling parasites to infest bee colonies by the parasite is discussed.

Sex, age and ovarian activity affect cuticular hydrocarbons in Diacamma ceylonense, a queenless ant

In the queenless ant, Diacamma ceylonense, the cuticular hydrocarbons (C25–C35) of nestmate workers vary in their proportions according to age and fertility. Newly eclosed adults (‘callows’) initially have the same cuticular profile, but with time this changes to that typical of foragers. In contrast, workers that begin to produce eggs develop a different cuticular profile. Several substances ( n-C29 and some methyl C25 and C27) discriminate these different social categories (callows, foragers and egg-layers). In Diacamma ceylonense, inter-colony variation of the cuticular hydrocarbons was much lower than intra-colony variation. We also found qualitative differences between the sexes, with males having a clearly different profile with much more alkanes. We discuss these results in the context of physiological models of the relation between ovarian activity and the synthesis of cuticular hydrocarbons. Variations in cuticular profile are a reliable reflection of ovarian activity, and could be used by ants as a fertility signal.

Modifications of the cuticular hydrocarbon profile of Apis mellifera worker bees in the presence of the ectoparasitic mite Varroa jacobsoni in brood cells.

Varroa jacobsoni is an ectoparasite of Apis mellifera which invades brood cells, on 8-day-old larvae several hours before cell capping. Reproduction of the parasite takes place in the capped brood cells during the nymphose of the bee. Cuticular hydrocarbons of unparasitized bees and of bees parasitized by Varroa jacobsoni were extracted and analysed by gas chromatography (GC) coupled with mass spectrometry (GC-MS). Three developmental stages of worker honey bees were studied: larvae, pupae and emergent adults. The comparison between unparasitized and parasitized hosts was performed with Principal Components Analysis coupled with a multivariate variance analysis. The cuticular hydrocarbon profiles of honey bees were qualitatively similar, for the 3 developmental stages and regardless of the presence of Varroa in the cells. Nevertheless, comparison of the relative proportions of hydrocarbons showed that the cuticular profiles of pupae and emergent adults parasitized by 1 mite and of larvae parasitized by 2 mites were significantly different from the corresponding unparasitized individuals. Such modifications could be regarded (i) as a cause of the multi-infestation in larvae during invasion of brood and (ii) as a consequence of stress and/or removal of proteins contained in the haemolymph of the host during its development.

Nestmate discrimination and cuticular profiles of a temporary parasitic ant Lasius sp. and its host L. fuliginosus (Hymenoptera, Formicidae)

Workers of the temporary parasitic ant Lasius sp. were perfectly compatible with their hosts Lasius fuliginosus. Aggression was never seen between allospecific nestmates in either field or laboratory. In the laboratory, trophallaxis and allogrooming between allospecific nestmates were statistically more frequent than that between conspecifics. These ants were highly aggressive toward individuals of either species from another mixed colony located 1 km away, indicating that they discriminated nestmates and nonnestmates regardless of the species to which they belonged. No aggressive actions, however, were observed between two neighboring mixed nests located 5 m apart. We have not considered, however, the relationship of the two neighboring nests: the two nests may have been two subunits of the same family or sister colonies, or may have been different colonies but discriminated from distant aliens. Gas chromatography analysis on the total cuticular extracts showed that Lasius sp. and L. fuliginosus possess distinct cuticular profiles, even though they were collected from the same mixed colony.

Social hackers: integration in the host chemical recognition system by a paper wasp social parasite.

Obligate social parasites in the social insects have lost the worker caste and the ability to establish nests. As a result, parasites must usurp a host nest, overcome the host recognition system, and depend on the host workers to rear their offspring. We analysed cuticular hydrocarbon profiles of live parasite females of the paper wasp social parasite Polistes sulcifer before and after usurpation of host nests, using the non-destructive technique of solid-phase micro-extraction. Our results reveal that hydrocarbon profiles of parasites change after usurpation of host nests to match the cuticular profile of the host species. Chemical evidence further shows that the parasite queen changes the odour of the nest by the addition of a parasite-specific hydrocarbon. We discuss the possible role of this in the recognition and acceptance of the parasite and its offspring in the host colony.

Cuticular hydrocarbons of the dampwood termite, Zootermopsis nevadensis : Caste differences and role of lipophorin in transport of hydrocarbons and hydrocarbon metabolites

The epicuticular and internal hydrocarbons (HC) from different castes of the dampwood termite Zootermopsis nevadensis were analyzed by gas chromatography–mass spectrometry. The epicuticular HC profiles of workers and alates contained large proportions of n-heneicosane (n-C21), 5-methylheneicosane (5-MeC21), and 5,17- and 5,15-dimethylheneicosane (5,17-, 5,15-diMeC21). Sixty-three HC peaks were identified as normal-, monomethyl-, dimethyl-, and trimethylalkanes up to 41 carbons long. The HC content of the internal tissues was significantly greater than on the epicuticle in all castes examined (2.8-fold in female alates, 5.7-fold in male alates, and 13.7-fold in workers). The hemolymph of all castes, including workers, soldiers, nymphs, and female and male alates, contained large amounts of HC and all hemolymph samples had nearly identical HC profiles. However, the hemolymph profile was remarkably different from the cuticular profile. KBr equilibrium gradient ultracentrifugation of worker hemolymph showed that all HC were associated with a high-density lipophorin (density of 1.12 ± 0.005 g/ml) consisting of two subunits, apolipophorin-I (220 kDa) and apolipophorin-II (82 kDa). After topical application of radiolabeled 3,11-dimethylnonacosane, a HC that is closely related to a native HC, all the internalized HC and radiolabeled lipid metabolites that were recovered from the hemolymph were associated with lipophorin. These findings are consistent with the hypothesis that lipophorin transports HC and some HC metabolites through the hemolymph from the sites of synthesis to the integument and from the integument to metabolic and excretory tissues. In many social insects, different castes have different relative proportions of the same HC and lipophorin appears to play an important role in regulation of the externalization and internalization of HC and, therefore, in the attainment of caste-specific chemical profiles.

Changes of species specific cuticular hydrocarbon profiles in the cockroaches Nauphoeta cinerea and Leucophaea maderae reared in heterospecific groups

AbstractThe cuticular hydrocarbon profiles of the cockroaches Nauphoeta cinerea and Leucophaea maderae are species‐specific when maintained in homospecific rearings. When individuals were reared in mixed species colonies, they initially remained in homospecific groups under different shelters. However, after 14 days they formed one heterospecific group with cuticular profiles showing characteristics of both species. When individuals were returned in monospecific rearings, their cuticular hydrocarbon profiles returned to species‐specific ones within 3 weeks.

Thief ants have reduced quantities of cuticular compounds in a ponerine ant, Ectatomma ruidum

Abstract. Workers of a tropical ponerine ant, Ectatomma ruidum (Roger), exhibit a system of intercolonial thievery for food; thief ants enter conspecific colonies, intercept food, and carry it to their own colony. We analysed thief ants, ants from the thief's colony, and ants from the colony being robbed to determine if changes in cuticular profiles could facilitate entry by thieves into a target colony. Thief ants have significantly lower total quantities of dichloromethane‐soluble cuticular compounds than non‐thieves. The reduction in cuticular compounds on thieves suggests that thievery is facilitated by inhibition of either synthesis or acquisition of its home colony's recognition cues. Five of the fifteen compounds differed significantly in their relative proportion among colonies. Principal components analysis lends support to the hypothesis that both inhibition of a thief's home colony cues and acquisition of its target colony's cues play a role in successful thievery.

Male dominant/subordinate relationships, cuticular profiles and sex pheromone in Nauphoeta cinerea (Dictyoptera, Blaberidae)

In the cockroach Nauphoeta cinerea, male-male aggressive interactions result in dominant-subordinate relationships. Once dominance relationships are established, a male can recognize the status of another individual, likely through chemical cues. The aim of this study was to determine the effect of these male-male interactions on cuticular chemical profiles and on the relative composition of the male sex pheromone. The results of chemical analyses of males reared in pairs for 30 days clearly showed significant differences in both cuticular profiles and sex pheromone of dominant and subordinate individuals. The possible role of these compounds as recognition cues was discussed.