Development of interspecific recognition behavior in the antsManica rubida andFormica selysi (Hymenoptera: Formicidae) reared in mixed-species groups

The purpose of this study was to determine the role of early social experience on the ontogeny of kin and nestmate recognition in ants by means of both behavioral and chemical analysis. Workers of two ant species,Manica rubida (Myrmicinae) andFormica selysi (Formicinae), were reared in homospecific groups (control) or in artificial heterospecific groups (mixed), created less than 5 h after their emergence. Recognition was evaluated between unfamiliar individuals of different species reared in control and mixed groups for periods of 5, 12, 24, 48, and 72 h and 8, 15, 30, 60, or 90 days after emergence. Heterospecifically reared individuals of both species gradually became tolerant of allospecific individuals from control groups. Moreover, homospecifically reared individuals did not aggress allospecific individuals reared in mixed groups. During the course of familiarization between the species, there were modifications of the chemical recognition signals. In mixed groups, hydrocarbon profiles of both species acquire gradually some of the components characteristic of their heterospecific nestmates. These experiments showed that allospecific recognition required the acquisition of a minimal quantity of allospecific cues. The phenomenon provided an another example of the relationship between tolerance and the chemical cues displayed by both species. The results suggested that the individual recognized the allospecific cues borne on each individual's body surface and/or that each individual learned and memorized allospecific cues during its early life. Therefore, each individual might develop a template encoding the allospecific and the conspecific cues to characterize nestmates.     

Learning and discrimination of cuticular hydrocarbons in a social insect

Social insect cuticular hydrocarbon (CHC) mixtures are among the most complex chemical cues known and are important in nest-mate, caste and species recognition. Despite our growing knowledge of the nature of these cues, we have very little insight into how social insects actually perceive and discriminate among these chemicals. In this study, we use the newly developed technique of differential olfactory conditioning to pure, custom-designed synthetic colony odours to analyse signal discrimination in Argentine ants, Linepithema humile. Our results show that tri-methyl alkanes are more easily learned than single-methyl or straight-chain alkanes. In addition, we reveal that Argentine ants can discriminate between hydrocarbons with different branching patterns and the same chain length, but not always between hydrocarbons with the same branching patterns but different chain length. Our data thus show that biochemical characteristics influence those compounds that ants can discriminate between, and which thus potentially play a role in chemical signalling and nest-mate recognition.     

Evolution of cuticular hydrocarbon diversity in ants

The cuticular hydrocarbons (CHCs) of ants provide important cues for nest-mate and caste recognition. There is enormous diversity in the composition of these CHCs, but the manner in which this diversity has evolved is poorly understood. We gathered data on CHC profiles for 56 ant species, relating this information to their phylogeny. We deduced the mode of evolution of CHC profiles by reconstructing character evolution and then relating the number of changes in CHC components along each branch of the phylogeny to the length of the branch. There was a strong correlation between branch length and number of component changes, with fewer changes occurring on short branches. Our analysis thereby indicated a gradual mode of evolution. Different ant species tend to use specific CHC structural types that are exclusive of other structural types, indicating that species differences may be generated in part by switching particular biosynthetic pathways on or off in different lineages. We found limited, and contradictory, evidence for abiotic factors (temperature and rainfall) driving change in CHC profiles.     

Workers and queens of the European hornetVespa crabro L. have colony-specific cuticular hydrocarbon profiles (Hymenoptera: Vespidae)

Summary Cuticular hydrocarbons were extracted from sixty individual workers from six colonies ofVespa crabro L. and analyzed by combined gas-chromatography/mass spectrometry. Discriminant analysis of the cuticular hydrocarbon profiles of workers and queens showed that the wasps could be grouped by colony and by caste. Stepwise discriminant analysis selected the components which were weighted most heavily in these analyses. Different combinations of cuticular hydrocarbons were important in grouping workers by colony, queens and workers by colony, and workers and queens by caste.     

Solid-phase microextraction and cuticular hydrocarbon differences related to reproductive activity in juniper bark borer Semanotus bifasciatus Motschulsky

Cuticular hydrocarbons of Cerambycidae species can function as signals for sex recognition. Little is known about the copulatory signals of the juniper bark borer Semanotus bifasciatus, a major economic threat to Platycladus orientalis Franco in China. Here, we investigated the cuticular hydrocarbons of both sexes of S. bifasciatus to determine the chemically mediated mating signals using the solid-phase microextraction (SPME) technique with carbowax/divinylbenzene fibers (CAR/DVB) and then analyzed by coupled gas chromatography-mass spectrometry (GC-MS). A series of aliphatic saturated straight-chain n-alkanes (n-C₂₃ to n-C₂₈), internally branched monomethylalkanes at carbons 3, 11, or 13, and dimethylalkanes were identified, which showed no qualitative differences in either sex and were similar in the samples with SPME fiber extraction and those with hexane extraction. The bioassay showed that 11-methylpentacosane (11-MeC₂₅), 11-methylhexacosane (11-MeC₂₆), and 11-methylheptacosane (11-MeC₂₇) have sex-specific recognition functions that triggered more mating attempts at a female-specific ratio of 100:4:60 than at a male-specific ratio of 100:85:50. In addition, the female-specific ratio of 11-methylalkanes can elicit about 70% of male mating attempts within about 60 s, whereas live females elicit about 98% of male mating attempts within 25 s. The discrepancy in the initiation of mating attempts by synthetic mixtures and live females suggests that the methyl isomers 3-MeC₂₅, 3-MeC₂₇, and/or 11,15-diMeC₂₇ may also be involved in the mating behavior of S. bifasciatus. These results suggest that 11-MeC₂₅, 11-MeC₂₆, and 11-MeC₂₇ constitute the contact sex pheromone of S. bifasciatus, with the presence or absence of 11-MeC₂₆ in particular playing an important role in mate recognition by males.     

Striking cuticular hydrocarbon dimorphism in the mason wasp Odynerus spinipes and its possible evolutionary cause (Hymenoptera: Chrysididae,Vespidae)

Cleptoparasitic wasps and bees smuggle their eggs into the nest of a host organism. Here the larvae of the cleptoparasite feed upon the food provision intended for the offspring of the host. As cleptoparasitism incurs a loss of fitness for the host organism (offspring of the host fail to develop), hosts of cleptoparasites are expected to exploit cues that alert them to potential cleptoparasite infestation. Cuticular hydrocarbons (CHCs) could serve as such cues, as insects inevitably leave traces of them behind when entering a nest. By mimicking the host''s CHC profile, cleptoparasites can conceal their presence and evade detection by their host. Previous studies have provided evidence of cleptoparasites mimicking their host''s CHC profile. However, the impact of this strategy on the evolution of the host''s CHC profile has remained unexplored. Here, we present results from our investigation of a host–cleptoparasite system consisting of a single mason wasp species that serves syntopically as the host to three cuckoo wasp species. We found that the spiny mason wasp (Odynerus spinipes) is able to express two substantially different CHC profiles, each of which is seemingly mimicked by a cleptoparasitic cuckoo wasp (i.e. Chrysis mediata and Pseudospinolia neglecta). The CHC profile of the third cuckoo wasp (Chrysis viridula), a species not expected to benefit from mimicking its host''s CHC profile because of its particular oviposition strategy, differs from the two CHC profiles of its host. Our results corroborate the idea that the similarity of the CHC profiles between cleptoparasitic cuckoo wasps and their hosts are the result of chemical mimicry. They further suggest that cleptoparasites may represent a hitherto unappreciated force that drives the evolution of their hosts'' CHCs.     

白蚁表皮碳氢化合物研究进展

近年来, 固相微萃取等现代技术的使用显著促进了白蚁表皮碳氢化合物研究的开展。至今, 已有约29种白蚁的表皮碳氢化合物组分得到鉴定, 分属于木白蚁科、 鼻白蚁科、 原白蚁科和白蚁科, 其组分主要为正烷烃、 含有不同数量甲基的支链烷烃及少量烯烃。白蚁表皮碳氢化合物不仅具有一定的科、 属特异性, 大多数种类还具备特有组分, 表明其可作为种间识别的指标。表皮碳氢化合物组分在种内个体识别方面的作用, 在低等白蚁中多获得了支持性结果, 但也有研究认为在这些种类中表皮碳氢化合物不是种内个体识别（同巢个体识别）的唯一指标。发现其与品级分化的相关是近年来白蚁表皮碳氢化合物研究的重要进展。有些种类表皮碳氢化合物的年消长与生殖蚁的分化有关; 而另一些种类生殖蚁含有表皮碳氢化合物特有组分, 其含量与生殖蚁的生殖状态有关, 提示其可能在品级分化中发挥重要作用。作为研究白蚁品级分化和维持机理的新方向, 表皮碳氢化合物值得进一步研究探索。     

The smell of parents: breeding status influences cuticular hydrocarbon pattern in the burying beetle Nicrophorus vespilloides

The waxy layer of the cuticle has been shown to play a fundamental role in recognition systems of insects. The biparental burying beetle Nicrophorus vespilloides is known to have the ability to discriminate between breeding and non-breeding conspecifics and also here cuticular substances could function as recognition cue. However, it has not yet been demonstrated that the pattern of cuticular lipids can reflect the breeding status of a beetle or of any other insect. With chemical analysis using coupled gas chromatography-mass spectrometry, we showed that the chemical signature of N. vespilloides males and females is highly complex and changes its feature with breeding status. Parental beetles were characterized by a higher amount of some unusual unsaturated hydrocarbons than beetles which are not caring for larvae. The striking correlation between cuticular profiles and breeding status suggests that cuticular hydrocarbons inform the beetles about parental state and thus enable them to discriminate between their breeding partner and a conspecific intruder. Furthermore, we found evidence that nutritional conditions also influence the cuticular profile and discuss the possibility that the diet provides the precursors for the unsaturated hydrocarbons observed in parental beetles. Our study underlines the fact that the cuticular pattern is rich of information and plays a central role in the burying beetles' communication systems.     

Low level of cuticular hydrocarbons in a parasitoid of a solitary digger wasp and its potential for concealment

Insect cuticular hydrocarbons (CHC) play a role as semiochemicals in many host–parasite systems and chemical mimicry or camouflage is a well-known mechanism of parasites to evade detection by the host. The cuckoo wasp Hedychrum rutilans (Hymenoptera, Chrysididae) is a parasitoid of larvae of the European beewolf Philanthus triangulum (Hymenoptera, Crabronidae). Females chemically mimic the cuticular hydrocarbons of their hosts to avoid detection and countermeasures when entering the host nest for oviposition. Here we report on a possible second mechanism of the chrysidid wasp H. rutilans to evade detection: the amount of CHC/mm² of cuticle is only approximately one-fifth compared to its beewolf host. Furthermore, we show that surprisingly large amounts of CHC of beewolf females can be found on the walls of the underground nest. Potentially, these hydrocarbons might constitute a background odor against which the cuckoo wasps or their chemical traces have to be perceived by the beewolf. The reduction in the amount of CHC of the cuckoo wasps might be equivalent to a dilution of recognition cues, especially against the background odor of the nest walls, and might provide a means to escape detection within the nest due to "chemical insignificance".     

Wax,sex and the origin of species: Dual roles of insect cuticular hydrocarbons in adaptation and mating

Evolutionary changes in traits that affect both ecological divergence and mating signals could lead to reproductive isolation and the formation of new species. Insect cuticular hydrocarbons (CHCs) are potential examples of such dual traits. They form a waxy layer on the cuticle of the insect to maintain water balance and prevent desiccation, while also acting as signaling molecules in mate recognition and chemical communication. Because the synthesis of these hydrocarbons in insect oenocytes occurs through a common biochemical pathway, natural or sexual selection on one role may affect the other. In this review, we explore how ecological divergence in insect CHCs can lead to divergence in mating signals and reproductive isolation. We suggest that the evolution of insect CHCs may be ripe models for understanding ecological speciation.     

Weak patriline effects are present in the cuticular hydrocarbon profiles of isolated Formica exsecta ants but they disappear in the colony environment

Chemical recognition cues are used to discriminate among species, con‐specifics, and potentially between patrilines in social insect colonies. There is an ongoing debate about the possible persistence of patriline cues despite evidence for the mixing of colony odors via a “gestalt” mechanism in social insects, because patriline recognition could lead to nepotism. We analyzed the variation in recognition cues (cuticular hydrocarbons) with different mating frequencies or queen numbers in 688 Formica exsecta ants from 76 colonies. We found no increase in the profile variance as genetic diversity increased, indicating that patriline effects were absent or possibly obscured by a gestalt mechanism. We then demonstrated that an isolated individual's profile changed considerably relative to their colony profile, before stabilizing after 5 days. We used these isolated individuals to eliminate the masking effects of the gestalt mechanism, and we detected a weak but statistically significant patriline effect in isolated adult workers and also in newly emerged callow workers. Thus, our evidence suggests that genetic variation in the cuticular hydrocarbon profile of F. exsecta ants (n‐alkanes and alkenes) resulted in differences among patrilines, but they were obscured in the colony environment, thereby avoiding costly nepotistic behaviors.     

水椰八角铁甲不同日龄和性别成虫表皮碳氢化合物的种类及动态

水椰八角铁甲Octodonta nipae(Maulik)是一种严重为害棕榈科植物的外来入侵害虫。为了明确日龄和性别等个体因素对水椰八角铁甲成虫表皮碳氢化合物的影响,本研究采用化学萃取法和气相色谱-质谱联用技术,分析了不同日龄的水椰八角铁甲雌、雄成虫表皮碳氢化合物的组成和含量。结果表明,水椰八角铁甲成虫的表皮碳氢化合物由21种C_(18)-C_(30)的碳氢化合物构成,包括11种正构烷烃、2种单甲基烷烃、1种多甲基烷烃、3种正构烯烃、1种单甲基烯烃和3种环烷烃。不同日龄和性别成虫的表皮碳氢化合物的组成种类相同,但是一些组分的含量有明显变化,例如1 d、5 d、10 d和15 d雌、雄成虫之间正二十四烷、正二十六烷、2-甲基十九烷和1-二十烯的含量存在显著差异。水椰八角铁甲成虫表皮碳氢化合物具有性二型,如性成熟雄虫的表皮的正二十烷、正二十一烷、正二十四烷、正二十六烷、2-甲基十九烷、10-甲基二十烷、1-二十烯和1-二十二烯的含量显著高于性成熟雌虫。本文的研究结果可为检验检疫过程中水椰八角铁甲近缘种,以及日龄、性别和性成熟的快速鉴定提供支持。     

Genetic and environmental influences on the cuticular hydrocarbon profiles of Goniozus wasps

The cuticular hydrocarbon (CHC) profiles of insects are well known to be variable. This variation may be due to genetic influences, environmental influences, or both. Most prior studies have focused on social insects, mainly those in the Hymenoptera, and have shown that hydrocarbons play an important role mediating social behaviour, particularly via kin recognition. Here, we assess the CHC profiles of three species of parasitoid wasps in the genus Goniozus (Hymenoptera: Bethylidae), some of which are known to attune their behaviour according to both environmentally based and genetically based recognition of kin. We find that CHC profiles vary according to both the genetic background (wasp species) and the developmental environment (host species) of individual parasitoids. This indicates that kin recognition could be based on CHC profiles in these parasitoids, as it is in social Hymenoptera. Because the CHC profiles of species within the genus Goniozus are dissimilar, we also conclude that chemical analysis could be used as a taxonomic tool alongside morphological and molecular genetic identification for Goniozus and other species.     

Endocrine control of cuticular hydrocarbon profiles during worker-to-soldier differentiation in the termite Reticulitermes flavipes

The social organization of termites, unlike that of other social insects, is characterized by a highly plastic caste system. With the exception of the alates, all other individuals in a colony remain at an immature stage of development. Workers in particular remain developmentally flexible; they can switch castes to become soldiers or neotenics. Juvenile hormone (JH) is known to play a key role in turning workers into soldiers. In this study, we analyzed differences in cuticular hydrocarbon (CHC) profiles among castes, paying particular attention to the transition of workers to soldiers, in the subterranean termite species Reticulitermes flavipes. CHCs have a fundamental function in social insects as they serve as cues in inter- and intraspecific recognition. We showed that (1) the CHC profiles of the different castes (workers, soldiers, nymphs and neotenics) are different and (2) when workers were experimentally exposed to a JH analog and thus induced to become soldiers, their CHC profiles were modified before and after the worker-presoldier molt and before and after the presoldier-soldier molt.     

Genetics of cuticular hydrocarbon differences between males of the parasitoid wasps Nasonia giraulti and Nasonia vitripennis

Many insects rely on cuticular hydrocarbons (CHCs) as major recognition signals between individuals. Previous research on the genetics of CHCs has focused on Drosophila in which the roles of three desaturases and one elongase were highlighted. Comparable studies in other insect taxa have not been conducted so far. Here, we explore the genetics of CHCs in hybrids of the jewel wasps Nasonia giraulti and Nasonia vitripennis. We analyzed the CHC profiles of pure strain and of F(2) hybrid males using gas chromatography coupled with mass spectrometry and distinguished 54 peaks, of which we identified 52 as straight-chain, monounsaturated, or methyl-branched CHCs. The latter compound class proved to be particularly abundant and diverse in Nasonia. Quantitative trait locus (QTL) analysis suggests fixed genetic differences between the two strains in 42 of the 54 studied traits, making Nasonia a promising genetic model for identifying genes involved in CHC biosynthesis. QTL for methyl-branched CHCs partly clustered in genomic regions with high recombination rate: a possible indication for pleiotropic genes that control their biosynthesis, which is largely unexplored so far. Finally, we identified and mapped genes in the Nasonia genome with high similarity to genes that have been implicated in alkene biosynthesis in Drosophila and discuss those that match in their position with predicted QTL for alkenes.     

Sex-specific genotype-by-environment interactions for cuticular hydrocarbon expression in decorated crickets, Gryllodes sigillatus: implications for the evolution of signal reliability

Phenotypic traits that convey information about individual identity or quality are important in animal social interactions, and the degree to which such traits are influenced by environmental variation can have profound effects on the reliability of these cues. Using inbred genetic lines of the decorated cricket, Gryllodes sigillatus, we manipulated diet quality to test how the cuticular hydrocarbon (CHC) profiles of males and females respond across two different nutritional rearing environments. There were significant differences between lines in the CHC profiles of females, but the effect of diet was not quite statistically significant. There was no significant genotype-by-environment interaction (GEI), suggesting that environmental effects on phenotypic variation in female CHCs are independent of genotype. There was, however, a significant effect of GEI for males, with changes in both signal quantity and content, suggesting that environmental effects on phenotypic expression of male CHCs are dependent on genotype. The differential response of male and female CHC expression to variation in the nutritional environment suggests that these chemical cues may be under sex-specific selection for signal reliability. Female CHCs show the characteristics of reliable cues of identity: high genetic variability, low condition dependence and a high degree of genetic determination. This supports earlier work showing that female CHCs are used in self-recognition to identify previous mates and facilitate polyandry. In contrast, male CHCs show the characteristics of reliable cues of quality: condition dependence and a relatively higher degree of environmental determination. This suggests that male CHCs are likely to function as cues of underlying quality during mate choice and/or male dominance interactions.     

Intraspecific variation in the cuticular hydrocarbons of the sandfly Phlebotomus perfiliewi from Italy

The cuticular hydrocarbons of Phlebotomus perfiliewi Parrot from representative localities on both sides of Italy show contrasts which support the view of Ward et al., (1981) that there are distinguishable populations of this sandfly on the Adriatic and Tyrrhenian coasts. It is suggested that the Appennine mountains form a barrier between the Adriatic and Tyrrhenian populations. A third distinct hydrocarbon type of P. perfiliewi was detected in Calabria, southern Italy, where contact between the Adriatic and Tyrrhenian types of flies is most likely to occur. P. perfiliewi from a trans-Appennine pass were also of the Calabrian hydrocarbon type. These hydrocarbon contrasts between allopatric populations of P. perfiliewi may result from clinical variation across the Appennines, associated with different host preferences, or they may represent apomictic populations with differential mate recognition systems.     

Agonistic behavior among colonies of the Formosan subterranean termite,Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), from Florida and Hawaii: Lack of correlation with cuticular hydrocarbon composition

Cuticular hydrocarbon patterns of the Formosan subterranean termite, Coptotermes formosanus Shiraki, were similar among colonies from the same geographical location. Hydrocarbon patterns of Florida colonies were easily distinguished from those of Hawaii colonies by using canonical discriminant analysis. Groups of termites from the same colony did not fight one another when placed in an arena. Intercolonial aggression was not recorded among C. formosanuspopulations from Florida but three colonies from Hawaii fought with the other Hawaiian and three Florida colonies. Of the 12 colonies (six each from Florida and Hawaii) tested, 3 Florida colonies did not direct or receive aggression from any other colony. Cuticular hydrocarbon patterns were not correlated with agonistic behavior.     

Characterization of age and cuticular hydrocarbon variation in mating pairs of house fly,Musca domestica,collected in the field

House flies, Musca domestica L., were collected in copula over two summers from six dairies located in three climatically distinct regions in the U.S.A. southern California, Minnesota and Georgia. Ages of males and females from a total of 511 mating pairs were estimated using pterin analysis. Cuticular hydrocarbon profiles and gonotrophic ages of females also were evaluated. Mean age of mating males ranged from 54 to 102 degree‐days (DD) (4–10 days based on field air temperatures), depending on the farm. Very young males (< 10–20 DD) and old males (> 200 DD) were rare in mating pairs. Mean female age at mating ranged from 20 to 46 DD (2.5–4 days). All mating females had eggs in the early stages of vitellogenesis and 99.2% were nulliparous. However, some older and parous females were collected, demonstrating that re‐mating can occur in the field. Head width measurements of mating pairs suggested that assortative mating by size did not occur. The cuticular hydrocarbon profiles of females were determined, with emphasis on (Z)‐9‐tricosene (muscalure). Overall, only 55% of mating females had detectable amounts (> 4 ηg per fly) of (Z)‐9‐tricosene. Of the females that had detectable (Z)‐9‐tricosene, variation in amount per female was high in all fly populations, and thus was not statistically related to the size or age of the mating female. The proportion of mating females with detectable levels of (Z)‐9‐tricosene varied by geographic region. Seventy‐one, 63, and 27% of females from southern California, Minnesota and Georgia had detectable amounts of (Z)‐9‐tricosene. Principal components analysis of the eight most abundant hydrocarbons from mating females, by state, revealed state‐level distinctiveness of hydrocarbons in house fly populations, which may reflect genetic variation associated with environmental stresses in those geographical zones.