Cuticular hydrocarbons in two parapatric species of ants and their hybrid

Discrimination between nestmates and non-nestmates in social insects is thought to rely on the pattern of cuticular hydrocarbons.We investigated the cuticular hydrocarbon profiles of 2 parapatric sibling ant species,Temnothorax nylanderi(Förster,1850)and Temnothorax crassispinus(Karavaiev,1926),and their hybrid.We found that although the profiles show considerable similarities,a discriminant analysis based on the relative peak areas of cuticular hydrocarbons separates the 3 taxa.The profiles of hybrids were not consistently intermediate between those of the paternal species,suggesting either non-additive interactions among the parental biosynthetic pathways or systematic differ-ences in environment-derived odor cues.

Analysis of sleep in individual Drosophila melanogaster reveals a self-regulatory role for cuticular hydrocarbons pheromones

It is well established that pheromones are used by insects to transmit infor-mation between individuals.However,research has revealed that individual insects can be both the sender and the receiver of some pheromonal signals.It is therefore interesting to consider whether the pheromonal state of an individual insect can exert an effect on itself.In this study,we monitored the sleep activity of single flies exhibiting a mutation that leads to pheromonal deficiency and found that cuticular hydrocarbons(CHs)exerted self-regulatory effects on the amount of sleep experienced by these flies.To identify the physiological significance of this mechanism,we compared the amounts of sleep in in-dividual young flies and individual old flies(flies are known to sleep less as they get older)and compared this data with young and old flies exhibiting mutations that lead to CH reception defects.The differences in the amount of sleep experienced by young and old mutant flies were significantly lower than those of the control flies.Our data show that hydrocarbon signals produced by the cuticle in Drosophila can be self-perceived and regulate the amount of sleep acquired in a maturation-dependent manner.

Chemical and behavioral analysis of the cuticular hydrocarbons from Asian citrus psyllid, Diaphorina citri

Huanglongbing （HLB） is the most destructive disease of citrus worldwide. The Asian citrus psyllid, Diaphorina citri Kuwayama （Hemiptera： Psyllidae）, is the vector of the phloem-inhabiting bacterium, Candidatus Liberibacter asiaticus, which is presumed to cause HLB in Florida citrus. Laboratory and field studies were conducted to examine the behavioral responses of male and female D. cirri to their cuticular extracts. In olfactometer assays, more male D. citri were attracted to one, five, or 10 female cuticular extract equivalent units than blank controls. The results were confirmed in field studies in which clear or yellow traps baited with 10 female cuticular extract equivalent units attracted proportionately more males than clear traps baited with male cuticular extract or unbaited traps. Analyses of cuticular constituents of male and female D. citri revealed differences between the sexes in chemical composition of their cuticular extracts. Laboratory bioassays with synthetic chemicals identified from cuticular extracts indicated that dodecanoic acid attracted more males than clean air. Traps baited with dodecanoic acid did not increase total catch olD. citri as compared with blank traps at the dosages tested; however, the sex ratio ofpsyllid catch was male biased on traps baited with the highest lure loading dosage tested （10.0 mg）.

Diapause affects cuticular hydrocarbon composition and mating behavior of both sexes in Drosophila montana

Envipnmental cues,mainly photoperiod and temperature,are known to control female adult reproductive diapause in several insect species.Diapause enhances female survival during adverse conditions and postpones progeny production to the favorable season.Male diapause(a reversible inability to inseminate receptive females)has been studied much less than female diapause.However,if the males maximized their chances to fertilize females while minimizing their energy expenditure,they would be expected to be in diapause at the same time as females.We investigated Drosophila montana male mating bchavior under short-day conditions that induce diapause in females and found the males to be reproductively inactive.We also found that males reared under long-day conditions(reproducing individuals)court reproducing postdiapause fermales,but not diapausing ones.The diapausing fies of both sexes had more long-chain and less short-chain hydrocarbons on their cuticle than the reproducing ones,which presumably increase their survival under stressful conditions,but at the same time decrease their attractiveness.Our study shows that the mating behavior of females and males is well coordinated during and afier overwintering and it also gives support to the dual role of insect cuticular hydrocarbons in adaptation and mate choice.

Evidence for a female-produced, long range pheromone of Anoplophora glabripennis （Coleoptera Cerambycidae）

Volatiles from female Asian longhorned beetle （ ALB ）, Anoplophora glabripenhis, were evaluated as candidate sex pheromone components. Previous studies on ALB have revealed several antennally active compounds from virgin females; however the origins and activity of these compounds were not apparent and require further investigation. We tested the hypothesis that one or more of the ALB contact sex pheromones is a precursor that undergoes abiotic oxidation to yield volatile pheromone components, and evaluated the activity of these compounds using laboratory and field bioassays. Gas chromatogra- phy coupled electroantennography detection （GC-EAD） analysis indicated the presence of three antennally active aldehydes （heptanal, nonanal, and hexadecanal） in female cuticular extracts exposed to ozone or UV and visible light. In laboratory bioassays using a Y-tube olfactometer, males were preferentially attracted to ozonized female body washes over crude body washes. Similarly, synthetic formulations of these compounds were preferred over controls in the olfactometer. Field trapping experiments conducted from 2006 to 2008 in Ningxia, China showed that synthetic lures of the three aldehydes formulated in a ratio simulating that of virgin females attracted more beetles compared to controls, and that combinations of these aldehydes, linalool oxide, and host kairomones captured more beetles than controls, and captured significantly more males.

Recognition of nestmate eggs in the ant Formicafusca is based on queen derived cues

Inclusive fitness benefits depend on recognizing the right individuals to interact with. Social insect nests protect themselves from non-kin intruders through nestmate recognition based on chemical cues. The recognition cues on adult individu- als are from a mixture of genetic and environmental sources, but the ontogeny and use of recognition cues on eggs has not been previously assessed. We studied recognition by workers of eggs that were either nestmates or non-nestmates, and the ontogeny of recognition cues on eggs in the ant Formica fusca, a species with precise egg recognition abilities. Workers were able to dis- criminate among freshly laid eggs with no nest derived cues on them, and the egg surface chemicals varied among nests in these eggs, suggesting that queen derived cues are used in nestmate recognition. The results are discussed in the light of their implica- tions on deceptive social parasite strategies and within colony conflicts

Hormonal modulation of reproduction and fertility signaling in polistine wasps

In social insects,it has been suggested that reproduction and the production of particular fertilitylinked cuticular hydrocarbons(CHC)may be under shared juvenile hormone(JH)control,and this could have been key in predisposing such cues to later evolve into full-fledged queen pheromone signals.However,to date,only few studies have experimentally tested this“hormonal pleiotropy”hypothesis.Here,we formally test this hypothesis using data from four species of Polistine wasps,Polistes dominula,Polistes satan,Mischocyttarus metathoracicus,and Mischocyttarus cassununga,and experimental treatments with JH using the JH analogue methoprene and the anti-JH precocene.In line with reproduction being under JH control,our results show that across these four species,precocene significantly decreased ovary development when compared with both the acetone solvent-only control and the methoprene treatment.Consistent with the hormonal pleiotropy hypothesis,these effects on reproduction were further matched by subtle shifts in the CHC profiles,with univariate analyses showing that in P.dominula and P.satan the abundance of particular linear alkanes and mono-methylated alkanes were affected by ovary development and our hormonal treatments.The results indicate that in primitively eusocial wasps,and particularly in Polistes,reproduction and the production of some CHC cues are under joint JH control.We suggest that pleiotropic links between reproduction and the production of such hydrocarbon cues have been key enablers for the origin of true fertility and queen signals in more derived,advanced eusocial insects.

Chemical deception among ant social parasites

Deception is widespread throughout the animal kingdom and various deceptive strategies are exemplified by social parasites. These are species of ants, bees and wasps that have evolved to invade, survive and reproduce within a host colony of another social species. This is achieved principally by chemical deception that tricks the host workers into treating the invading parasite as their own kin. Achieving levels of acceptance into typically hostile host colonies requires an amazing level of decep- tion as social insects have evolved complex species- and colony-specific recognition systems. This allows the detection of for- eigners, both hetero- and con-specific. Therefore, social parasitic ants not only have to overcome the unique species recognition profiles that each ant species produces, but also the subtle variations in theses profiles which generate the colony-specific profiles We present data on the level of chemical similarity between social parasites and their hosts in four different systems and then discuss these data in the wider context with previous studies, especially in respect to using multivariate statistical methods when looking for differences in these systems.

Asymmetrical positive assortative mating induced by developmental lead （Pb2＋） exposure in a model system, Drosophila melanogaster

Anthropogenic pollutants have the potential to disrupt reproductive strategies. Little is known about how lead （Pb2＋） exposure disrupts individual-level responses in reproductive behaviors, which are important for fitness. Drosophila melanogaster was used as a model system to deter- mine the effects of： 1） developmental lead exposure on pre-mating reproductive behaviors （i.e., mate preference）, and 2） lead exposure and mating preferences on fitness in the F0 parental generation and F1 un-exposed offspring. Wild-type strains of D. melanogaster were reared from egg stage to adulthood in control or leaded medium （250 μM PbAc） and tested for differences in： mate preference, male song performance, sex pheromone expression, fecundity, mortality, and body weight. F0 leaded females preferentially mated with leaded males （i.e., asymmetrical positive assortative mating） in 2-choice tests. This positive assortative mating was mediated by the females （and not the males） and was dependent upon context and developmental exposure to Pb. Neither the courtship song nor the sex pheromone profile expressed by control and leaded males medi- ated the positive assortative mating in leaded females. Leaded females did not incur a fitness cost in terms of reduced fecundity, increased mortality, or decreased body weight by mating with leaded males. These results suggest that sublethal exposure to lead during development can alter mate preferences in adults, but not fitness measures once lead exposure has been removed. We suggest that changes in mate preference may induce fitness costs, as well as long-term population and multi-generational implications, if pollution is persistent in the environment.

Comparative morphometric and chemical analyses of phenotypes of two invasive ambrosia beetles （Euwallacea spp.） in the United States

The polyphagous shot hole borer （PSHB）, Euwallacea sp., was first detected in 2003 in Los Angeles County, California, USA. Recently, this invasive species has become a major pest of many hardwood trees in urban and wildland forests throughout southern California. PSHB is nearly identical in morphology and life history to the tea shot hole borer （TSHB）, Euwallaceafornicatus, an invasive pest of hardwoods in Florida, USA and many other parts of the world. However, molecular studies have suggested that the taxa are different species. We conducted morphometric and chemical analyses of the pheno- types of Euwallacea sp. collected in southern California （Los Angeles County） and E. fornicatus collected in Florida （Miami-Dade County）. Our analyses indicated that PSHB has 3 larval instars. The third larval instar was separated from the first 2 instars by head capsule width with 0 probability of misclassification. The body length, head width, and pronotal width of PSHB adult males were significantly less than those of females. Head width and pronotal width of female PSHB were significantly less than those of female TSHB. In contrast, body length, and ratio of body length to pronotal width of female PSHB were significantly greater than those of female TSHB. However, females of these 2 species could not be separated completely by these 4 measurements because of the overlapping ranges. Cuticular hydrocarbons detected in both species were exclusively alkanes （i.e., n-alkanes, monomethylalkanes, dimethylalkanes, and trimethylalkanes）. Cuticular hydro- carbon profiles of PSHB males and females were similar, but they both differed from that of TSHB females. Cuticular hydrocarbons of PSHB were predominantly internally branched dimethylalkanes with backbones of 31 and 33 carbons, whereas cuticular hydro- carbons of TSHB females were dominated by internally branched monomethylalkanes and dimethylalkanes with backbones of 28 and 29 carbons. Multiple compounds within these classes appear to be diagnostic for PSHB and TSHB, respectively.

Discrimination of conspecifics from heterospecifics in a hybrid zone: Behavioral and chemical cues in ants

Species and nestmate recognition in social insects occurs mostly through cuticular hydrocarbons acting as chemical cues. These compounds generate a colony-specific odor profile depending on genetic and environmental factors. Species and nestmate recognition results in specific behavioral responses, regulating the level of aggression toward other individuals during an interaction. Although species discrimination and recognition cues have been poorly studied in the context of interspecific hybridization, such systems offer an opportunity to further investigate the influence of heritable and environmental factors on recognition. We explored the strength of discrimination in a hybrid zone between two ant species—Tetramorium immigrans and T. caespitum—by comparing cuticular hydrocarbon profiles and measuring intra- and interspecific worker aggression in both areas of sympatry and areas of allopatry among species. Species cuticular hydrocarbon profiles were well-differentiated and interspecific aggression was high, revealing highly discriminating species recognition cues. Hybrids’ cuticular hydrocarbon profiles consisted of a mixture of the parental bouquets, but also exhibited hybrid-specific patterns. Behavioral assays showed that T. immigrans is as aggressive toward hybrids as toward heterospecifics. Finally, aggression between heterospecific workers was lower when interacting individuals came from areas of sympatry among species than from areas of allopatry. Taken as a whole, these findings paint a particularly complex picture of the recognition system in T. immigrans, T. caespitum, and their hybrids, and highlight that hybrid zones afford a still underexplored opportunity for investigating recognition mechanisms and discrimination between species.

Self-referent phenotype matching and its role in female mate choice in arthropods

A growing body of empirical evidence shows that females of many animal species gain benefits by mating polyan- drously, and often prefer to mate with novel males over previous mates. Although a female preference for novel males has been ,demonstrated for multiple animal taxa, the mechanisms used by females to discriminate between novel and previous mates remain largely unknown. However, recent studies suggest that in decorated crickets Gryllodes sigillatus, females actually imbue males with their own chemical cues, known as cuticular hydrocarbons （CHCs） during mating, and utilize chemosensory self-referencing 1：o recognize recent mates. Here we review evidence that self-referent phenotype matching is a widespread mechanism of recogni- tion in arthropods, and explore how CHCs are used to facilitate mate-choice decisions. There is substantial evidence that CHCs are used as recognition cues to discriminate between species, kin, sexes, mates, individuals, and self and non-self, and are used to facilitate mate-choice decisions in a wide range of arthropod taxa. There is also evidence that CHCs are often transferred between individuals during direct physical contact, including copulation. Chemosensory self-referencing via cuticular hydrocarbons could provide a simple, but reliable mechanism for identifying individuals from previous mating encounters. This mechanism does not require any specialized cognitive abilities because an individual＇s phenotype is always available for reference. Given the ubiqui- tous use of CHCs among arthropods, chemosensory self-referencing may be a widespread mechanism used by female arthropods to facilitate ibmale mate-choice decisions and to enhance opportunities for polyandry [Current Zoology 59 （2）： 239-248, 2013].

The Guianese population of the fire ant Solenopsis saevissima is unicolonial

In this study, conducted in French Guiana, a part of the native range of the fire ant Solenopsis saevissima, we compared the cuticular hydrocarbon profiles of media workers with previous results based on intraspecific aggressiveness tests. We noted a strong congruence between the two studies permitting us to delimit 2 supercolonies extending over large distances （up to 54 kin）, a phenomenon known as unicoloniality. Solenopsis geminata workers, taken as an out-group for cluster analyses, have a very different cuticular hydrocarbon profile. Because S. saevissima has been reported outside its native range, our conclusion is that this species has the potential to become invasive because unicoloniality （i.e., the main attribute for ants to become invasive） was shown at least for the Guianese population.