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Abstract Background Brood parasites can exert strong selection pressure on their hosts. Many brood parasites escape their detection by mimicking sensory cues of their hosts. However, there is little evidence whether or not the hosts are able to escape the parasites’ mimicry by changing these cues. We addressed this question by analyzing cuticular hydrocarbon (CHC) profiles of Cerceris and Philanthus wasps and their brood parasites, cuckoo wasps mimicking the CHC profiles of their hosts. Some of these hosts use hydrocarbons to preserve their prey against fungal infestation and thus, they cannot significantly change their CHC composition in response to chemical mimicry by Hedychrum brood parasites. Results We found that the CHC overlap between brood parasites and their hosts was lower in case of host wasps not preserving their prey than in case of prey-preserving host wasps, whose CHC evolution is constrained. Furthermore, the CHC profiles in non-preserving host wasps is more strongly diversified in females than in males, thus in the sex that is chemically mimicked by brood parasites. Conclusion Our results provide evidence for a chemical arms race between those hosts that are liberated from stabilizing selection on their chemical template and their parasites.

Although recognition using cuticular chemistry is important for host–parasite interactions within aculeate Hymenoptera, cuticular hydrocarbon (CHC) profiles of only a few host–parasite pairs were characterized and compared. One largely neglected family in this context is the Mutillidae (velvet ants), whose species are ectoparasitoids of bees and wasps. In our study, we characterized and compared the CHC profiles of five species of Mutillidae and seven host species. The CHC profile of velvet ants differed among species and included large proportions of n-alkanes and methyl-branched alkanes. Alkenes were much less abundant in the CHC profiles of three species of velvet ants compared with their hosts, while the other two species possess a much lower abundance of methyl-branched alkanes than their hosts. Both the number of peaks and compound diversity were generally higher in velvet ants compared with their hosts. Thus, CHC profiles of parasitoids did not show signs of mimicry when compared with their hosts. In dyadic encounters between one species of velvet ant and its host bee species, the parasitoid mainly avoided interacting, while aggression by the host was rare. Our results suggest that velvet ants did not evolve chemical mimicry, perhaps in accordance with their wide host spectrum which would limit chemical specialization. However, the reduction of alkenes in social bee-attacking species and the reduction of methyl-branched alkanes in social wasp-attacking species may favour host nest invasion, since these two CHC classes are known to be important in nestmate recognition for social bees and wasps, respectively. A larger, phylogeny-corrected comparison of Mutillidae and hosts may help clarifying the evolution of the CHC profile of these parasitoids. [ABSTRACT FROM AUTHOR]

Deceptive pollination has been reported in the genus Aristolochia, but the floral biology and pollination strategy of A. bianorii, an endemic of the Balearic Islands, have not yet been studied. Here, we investigated floral anthesis, mating system, pollinators and volatile organic compounds (VOCs) emitted by its flowers.Flower buds were marked and monitored daily to define floral stages and their duration. Experimental bagging and hand‐pollination were performed to test for autonomous self‐pollination, induced self‐pollination and cross‐pollination. Flowers were collected to analyse the presence of entrapped pollinators. VOCs emitted by flowers were evaluated by means of solid phase microextraction followed by immediate GC–MS.Anthesis lasted between 63 and 96 h, and the species exhibited autonomous self‐pollination with moderate inbreeding depression. Pollinators were mainly females of Oscinomorpha longirostris (Diptera; Chloropidae). The number of pollinators inside flowers was affected by floral stage and time of flowering. The most common VOCs were alkanes, oximes, esters, alkenes, cyclic unsaturated hydrocarbons, isocyanates, amides and carboxylic acids.Aristolochia bianorii can set seed by autonomous self‐pollination, in contrast to other Aristolochia species, in which both protogyny and herkogamy prevent autonomous self‐pollination. However, the species may encourage cross‐pollination by attracting female chloropid flies though emission of floral scents that may mimic an oviposition site and, possibly, freshly killed true bugs (i.e. Heteroptera). In conclusion, A. bianorii promotes cross‐pollination, but delayed autonomous self‐pollination assures reproductive success in the putative absence of pollinators. [ABSTRACT FROM AUTHOR]

A vast diversity of parasites associates with ants. Living in and around ant nests of these organisms must overcome ant colony defenses. As ant defensive behavior is mainly mediated by species-specific cuticular hydrocarbons (CHCs) or alarm pheromones, and ant-associated parasites can either crack their hosts' chemical communication code by modifying their own CHC profiles or use pro-active strategies like chemical weaponry for distraction and repellency. While the chemical nature of ant–parasite interactions has been intensively studied for highly host-specific parasites, the chemical-deceptive strategies of the rather rare ant-resembling heteropterans are unknown. To gain insight into this system, I studied the bug Scolopostethus pacificus (Barber 1918) which can be found near the nests of the ecologically dominant and aggressive velvety tree ant (Liometopum occidentale, Emery 1895). Using behavioral, chemical, and molecular approaches, I disentangled the relationship of S. pacificus and its host ant. Chemical profiling of the bug and the ant revealed that the bug does not make use of CHC insignificance or mimicry, but instead uses a cocktail of volatile compounds released from its metathoracic glands that likely moderates encounters with its aggressive host. Feeding trials with armed and artificially disarmed bugs revealed a defensive function of the gland exudates. Targeted molecular gut barcoding showed that S. pacificus does not feed on L. occidentale. These results suggest that chemical weaponry, rather than a chemical code-cracking CHC matching or chemical insignificance, enables S. pacificus to get along with and live in close proximity to its host ant. [ABSTRACT FROM AUTHOR]

Abstract Background Ant colonies are plagued by a diversity of arthropod guests, which adopt various strategies to avoid or to withstand host attacks. Chemical mimicry of host recognition cues is, for example, a common integration strategy of ant guests. The morphological gestalt and body size of ant guests have long been argued to also affect host hostility, but quantitative studies testing these predictions are largely missing. We here evaluated three guest traits as triggers of host aggression—body size, morphological gestalt, and accuracy in chemical mimicry—in a community of six Eciton army ant species and 29 guest species. We quantified ant aggression towards 314 guests in behavioral assays and, for the same individuals, determined their body size and their accuracy in mimicking ant cuticular hydrocarbon (CHC) profiles. We classified guests into the following gestalts: protective, myrmecoid, staphylinid-like, phorid-like, and larval-shaped. We expected that (1) guests with lower CHC mimicry accuracy are more frequently attacked; (2) larger guests are more frequently attacked; (3) guests of different morphological gestalt receive differing host aggression levels. Results Army ant species had distinct CHC profiles and accuracy of mimicking these profiles was variable among guests, with many species showing high mimicry accuracy. Unexpectedly, we did not find a clear relationship between chemical host similarity and host aggression, suggesting that other symbiont traits need to be considered. We detected a relationship between the guests’ body size and the received host aggression, in that diminutive forms were rarely attacked. Our data also indicated that morphological gestalt might be a valuable predictor of host aggression. While most ant-guest encounters remained peaceful, host behavior still differed towards guests in that ant aggression was primarily directed towards those guests possessing a protective or a staphylinid-like gestalt. Conclusion We demonstrate that CHC mimicry accuracy does not necessarily predict host aggression towards ant symbionts. Exploitation mechanisms are diverse, and we conclude that, besides chemical mimicry, other factors such as the guests’ morphological gestalt and especially their body size might be important, yet underrated traits shaping the level of host hostility against social insect symbionts.

While most ant species establish a colony independently, some socially parasitic ants build the foundation of their colony by invading other ant (host) colonies and utilizing their labor forces. Many socially parasitic ants disguise their cuticular hydrocarbon (CHC) profile, which is also known as signature mixture for nestmate discrimination, when invading the host colony. Since the strategy of chemical disguise is widespread in socially parasitic ants, elucidating the mechanism of chemical disguise will promote knowledge on the evolutionary history of social parasitism. However, detailed knowledge is still lacking, as the relevant information has only originated from circumstantial evidence, which was obtained from ecological observations. In this study, we investigated the mechanism of chemical disguise in a new queen of a temporary socially parasitic spiny ant (Polyrhachis lamellidens) by measuring its CHC profile, performing a tracing assay with labeled substances, and analyzing gene expression levels. First, after rubbing behavior was observed against the host workers, the CHC profile in P. lamellidens shifted to pronounced peaks that closely resembling that of the host workers. We also observed a reduction in aggressive behaviors by the host ant against P. lamellidens after rubbing behavior was performed. In addition, P. lamellidens acquired artificially-applied labeling substances from host workers through their rubbing behaviors, while gene expression profiling showed the expression of CHC synthesis-related genes did not change during this behavior. These results suggest that P. lamellidens directly obtains host CHCs through rubbing behavior, and these host CHCs enables P. lamellidens to remain disguised during colony invasion.

The small hive beetle, Aethina tumida (Coleoptera: Nitidulidae), is an economically important pest of the Western honeybee, Apis mellifera (Hymenoptera: Apidae). We investigated the effect of rearing environment on the cuticular chemical profile of adult A. tumida, using hexane to extract the hydrocarbons and other compounds from the cuticles of beetles. Beetles were collected from A. mellifera colonies in Australia as well as reared in single sex laboratory cultures on different diets. We investigated whether rearing environment (laboratory vs. field, different apiaries, access to mating partners, diet) had any effect on cuticular hydrocarbons. Coupled gas chromatography–mass spectrometry analyses of the extracts showed that rearing environment had significant qualitative and quantitative effects on the hydrocarbons detected. The data support the hypothesis that cuticular profiles of A. tumida are contingent on environment, partitioning on the basis of rearing diet and source hives. The finding has implications for the regulation of interactions between A. tumida and honeybees and improvements in targeting of management strategies. [ABSTRACT FROM AUTHOR]

Deceptive flowers, unlike in mutualistic pollination systems, mislead their pollinators by advertising rewards which ultimately are not provided. Although our understanding of deceptive pollination systems increased in recent years, the attractive signals and deceptive strategies in the majority of species remain unknown. This is also true for the genus Aristolochia, famous for its deceptive and fly-pollinated trap flowers. Representatives of this genus were generally assumed to be oviposition-site mimics, imitating vertebrate carrion or mushrooms. However, recent studies found a broader spectrum of strategies, including kleptomyiophily and imitation of invertebrate carrion. A different deceptive strategy is presented here for the western Mediterranean Aristolochia baetica L. We found that this species is mostly pollinated by drosophilid flies (Drosophilidae, mostly Drosophila spp.), which typically feed on fermenting fruit infested by yeasts. The flowers of A. baetica emitted mostly typical yeast volatiles, predominantly the aliphatic compounds acetoin and 2,3-butandiol, and derived acetates, as well as the aromatic compound 2-phenylethanol. Analyses of the absolute configurations of the chiral volatiles revealed weakly (acetoin, 2,3-butanediol) to strongly (mono- and diacetates) biased stereoisomer-ratios. Electrophysiological (GC-EAD) experiments and lab bioassays demonstrated that most of the floral volatiles, although not all stereoisomers of chiral compounds, were physiologically active and attractive in drosophilid pollinators; a synthetic mixture thereof successfully attracted them in field and lab bioassays. We conclude that A. baetica chemically mimics yeast fermentation to deceive its pollinators. This deceptive strategy (scent chemistry, pollinators, trapping function) is also known from more distantly related plants, such as Arum palaestinum Boiss. (Araceae) and Ceropegia spp. (Apocynaceae), suggesting convergent evolution. In contrast to other studies working on floral scents in plants imitating breeding sites, the present study considered the absolute configuration of chiral compounds. [Display omitted] • Main pollinators of deceptive Aristolochia baetica are drosophilid flies. • The flowers release a scent resembling yeast-fermenting fruits. • Main compounds are acetoin, 2,3-butanediol monoacetate and related chemicals. • Some but not all of the chiral compounds are dominated by a single stereoisomer. • Most compounds but not all stereoisomers were biologically active in pollinators. [ABSTRACT FROM AUTHOR]

Background: Ant colonies are plagued by a diversity of arthropod guests, which adopt various strategies to avoid or to withstand host attacks. Chemical mimicry of host recognition cues is, for example, a common integration strategy of ant guests. The morphological gestalt and body size of ant guests have long been argued to also affect host hostility, but quantitative studies testing these predictions are largely missing. We here evaluated three guest traits as triggers of host aggression—body size, morphological gestalt, and accuracy in chemical mimicry—in a community of six Eciton army ant species and 29 guest species. We quantified ant aggression towards 314 guests in behavioral assays and, for the same individuals, determined their body size and their accuracy in mimicking ant cuticular hydrocarbon (CHC) profiles. We classified guests into the following gestalts: protective, myrmecoid, staphylinid-like, phorid-like, and larval-shaped. We expected that (1) guests with lower CHC mimicry accuracy are more frequently attacked; (2) larger guests are more frequently attacked; (3) guests of different morphological gestalt receive differing host aggression levels. Results: Army ant species had distinct CHC profiles and accuracy of mimicking these profiles was variable among guests, with many species showing high mimicry accuracy. Unexpectedly, we did not find a clear relationship between chemical host similarity and host aggression, suggesting that other symbiont traits need to be considered. We detected a relationship between the guests' body size and the received host aggression, in that diminutive forms were rarely attacked. Our data also indicated that morphological gestalt might be a valuable predictor of host aggression. While most ant-guest encounters remained peaceful, host behavior still differed towards guests in that ant aggression was primarily directed towards those guests possessing a protective or a staphylinid-like gestalt. Conclusion: We demonstrate that CHC mimicry accuracy does not necessarily predict host aggression towards ant symbionts. Exploitation mechanisms are diverse, and we conclude that, besides chemical mimicry, other factors such as the guests' morphological gestalt and especially their body size might be important, yet underrated traits shaping the level of host hostility against social insect symbionts. [ABSTRACT FROM AUTHOR]

1. A diverse group of arthropods have adapted to the niches found inside the nests of social insects. Studies mostly focused on very specialised parasites residing in the brood chambers. However, the biology and strategies of symbionts occupying other niches, such as waste dumps, are underexplored. 2. Using a series of complementary experiments, this study demonstrated that the Mediterranean beetle Oochrotus unicolor has adapted to the waste dump niche found in the nests of Messor harvester ants. 3. Laboratory experiments confirmed field observations that the beetle preferentially resided in the refuse pits. Next, it was shown that the beetles readily consumed seeds and flour, whereas other food sources were poorly accepted and ant brood was never even eaten. The beetles did not elicit a strong aggression response in Messor ants, and they could tolerate very high densities of workers without clear costs. The beetles modestly mimicked the nest recognition cues of their Messor host. This imperfect mimicry could promote the adoption of the beetle in the ant colony, in concert with mechanical defence generated by its tank‐like body. Isolation of the beetle from its host did not significantly affect the beetle's chemical cuticular profile nor did it provoke elevated ant aggression, indicating that the beetle does not acquire the chemicals passively from its host. 4. This paper discusses the fact that waste dumps in social insect nests are hotspots for arthropod symbionts. It shows that symbionts in this niche may employ behavioural, trophic and chemical strategies that are different from those found in other niches of social insect nests. [ABSTRACT FROM AUTHOR]

Abstract Host-symbiont interactions are embedded in ecological communities and range from unspecific to highly specific relationships. Army ants and their arthropod guests represent a fascinating example of species-rich host-symbiont associations where host specificity ranges across the entire generalist - specialist continuum. In the present study, we compared the behavioral and chemical integration mechanisms of two extremes of the generalist - specialist continuum: generalist ant-predators in the genus Tetradonia (Staphylinidae: Aleocharinae: Athetini), and specialist ant-mimics in the genera Ecitomorpha and Ecitophya (Staphylinidae: Aleocharinae: Ecitocharini). Similar to a previous study of Tetradonia beetles, we combined DNA barcoding with morphological studies to define species boundaries in ant-mimicking beetles. This approach found four ant-mimicking species at our study site at La Selva Biological Station in Costa Rica. Community sampling of Eciton army ant parasites revealed that ant-mimicking beetles were perfect host specialists, each beetle species being associated with a single Eciton species. These specialists were seamlessly integrated into the host colony, while generalists avoided physical contact to host ants in behavioral assays. Analysis of the ants’ nestmate recognition cues, i.e. cuticular hydrocarbons (CHCs), showed close similarity in CHC composition and CHC concentration between specialists and Eciton burchellii foreli host ants. On the contrary, the chemical profiles of generalists matched host profiles less well, indicating that high accuracy in chemical host resemblance is only accomplished by socially integrated species. Considering the interplay between behavior, morphology, and cuticular chemistry, specialists but not generalists have cracked the ants’ social code with respect to various sensory modalities. Our results support the long-standing idea that the evolution of host-specialization in parasites is a trade-off between the range of potential host species and the level of specialization on any particular host.

Various organisms, especially arthropods, are able to live as parasites in ant nests and to prey upon ant broods without eliciting any aggressive behaviour in the hosts. Understanding how these intruders are able to break the ants' communication codes in their favour represents a challenging and intriguing evolutionary question. We studied the chemical strategies of three European hoverfly species, Microdon mutabilis (parasitic on Formica cunicularia), M. analis (parasitic on Lasius emarginatus) and M. devius (parasitic on L. distinguendus). The peculiar slug-like larvae of these three species live inside ant nests feeding upon their broods. Gas chromatography-mass spectrometry analyses show that: 1) these parasites mimic the host brood rather than the ant workers, although each differs distinctly in the extent of chemical mimicry; 2) isolation experiments indicate that after 14 days the responsible cuticular hydrocarbons (CHCs) are not passively acquired but synthesized by the fly larvae. Additionally, Microdon larvae show an array of protective structural features, such as a thick and multi-layered cuticle, retractable head, dome-shaped tergum and a flat and strongly adhesive "foot" (sternum). This combination of protective chemical and structural features represents a successful key innovation by Microdon species, and one that may facilitate host switching. The results of a preliminary adoption analysis confirm that Microdon larvae of at least some species can readily be accepted by different species of ants. [ABSTRACT FROM AUTHOR]

Summary: Deception of floral visitors in pollination systems is widely distributed among flowering plants. In deceptive systems, the flower (or part of it) or inflorescence mimics either a specific or an unspecific model to attract pollinators.A previous study showed that Telipogon peruvianus flowers developed sexual deception for pollination. However, it was unknown which stimuli were playing a role in pollination. Therefore, we aim to throw some light onto these questions using colour and chemical analysis and biotests.Interestingly, using spectral reflectance, we show here that the flowers present high contrast similar to that produced by a female tachinid fly sitting on a daisy inflorescence, which is used as food resource. We also tested the role of chemical signals in pollinator attraction by collecting floral and female extracts for chemical and electrophysiological analyses, and carried out behavioural tests. For biotests, various treatments, including synthetic mixtures of the electrophysiologically active compounds found in common in females and flowers, have demonstrated that T. peruvianus flowers mimic the sexual pheromone of their pollinator's females.Thus, we give evidence that T. peruvianus flowers mimic a model composed of two organisms. Our study contributes to the understanding of the evolution of deceptive pollination. [ABSTRACT FROM AUTHOR]

Summary: Despite the phylogenetic distance between plants and insects, these two groups of organisms produce some secondary metabolites in common. Identical structures belonging to chemical classes such as the simple monoterpenes and sesquiterpenes, iridoid monoterpenes, cyanogenic glycosides, benzoic acid derivatives, benzoquinones and naphthoquinones are sometimes found in both plants and insects. In addition, very similar glucohydrolases involved in activating two‐component defenses, such as glucosinolates and cyanogenic glycosides, occur in both plants and insects. Although this trend was first noted many years ago, researchers have long struggled to find convincing explanations for such co‐occurrence. In some cases, identical compounds may be produced by plants to interfere with their function in insects. In others, plant and insect compounds may simply have parallel functions, probably in defense or attraction, and their co‐occurrence is a coincidence. The biosynthetic origin of such co‐occurring metabolites may be very different in insects as compared to plants. Plants and insects may have different pathways to the same metabolite, or similar sequences of intermediates, but different enzymes. Further knowledge of the ecological roles and biosynthetic pathways of secondary metabolites may shed more light on why plants and insects produce identical substances. [ABSTRACT FROM AUTHOR]

Sphecophaga vesparum often parasitizes nests of vespid wasps such as Vespula vulgaris and Vespula germanica. Inside the colonies, the ectoparasitic larvae feed on the immature forms of the wasps. There are two adult forms of S. vesparum. The large, winged adults emerge from either rigid yellow cocoons or the orange cocoons used for overwintering. The small, brachypterous females emerge from soft, white cocoons. The species is facultative deuterotokous, producing mostly parthenogenic females and infrequently producing males. Here, we describe the production of chemical compounds related to the different developmental forms of the parasitoid S. vesparum (larvae, pupae and adults). We also compare the chemical profiles of the parasitoid wasp adults to those of their two main host species, Vespula vulgaris and Vespula germanica. The results show differences in hydrocarbon composition of larvae, pupae and adults of S. vesparum. Our results also suggest a partial mimicry of each of the two host species, mostly relating to linear alkanes present in both parasitoids and the host vespid wasp species. This matching is likely due to the recycling of the prey’s hydrocarbons, as has been found in other species of parasitoids.

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. [ABSTRACT FROM AUTHOR]

Insect brood parasites have evolved a variety of strategies to avoid being detected by their hosts. Few previous studies on cuckoo wasps (Hymenoptera: Chrysididae), which are natural enemies of solitary wasps and bees, have shown that chemical mimicry, i.e., the biosynthesis of cuticular hydrocarbons (CHC) that match the host profile, evolved in several species. However, mimicry was not detected in all investigated host-parasite pairs. The effect of host range as a second factor that may play a role in evolution of mimicry has been neglected, since all previous studies were carried out on host specialists and at nesting sites where only one host species occurred. Here we studied the cuckoo wasp Parnopes grandior, which attacks many digger wasp species of the genus Bembix (Hymenoptera: Crabronidae). Given its weak host specialization, P. grandior may either locally adapt by increasing mimicry precision to only one of the sympatric hosts or it may evolve chemical insignificance by reducing the CHC profile complexity and/or CHCs amounts. At a study site harbouring three host species, we found evidence for a weak but appreciable chemical deception strategy in P. grandior. Indeed, the CHC profile of P. grandior was more similar to all sympatric Bembix species than to a non-host wasp species belonging to the same tribe as Bembix. Furthermore, P. grandior CHC profile was equally distant to all the hosts’ CHC profiles, thus not pointing towards local adaptation of the CHC profile to one of the hosts’ profile. We conducted behavioural assays suggesting that such weak mimicry is sufficient to reduce host aggression, even in absence of an insignificance strategy, which was not detected. Hence, we finally concluded that host range may indeed play a role in shaping the level of chemical mimicry in cuckoo wasps.

Social insect colonies provide a valuable resource that attracts and offers shelter to a large community of arthropods. Previous research has suggested that many specialist parasites of social insects chemically mimic their host in order to evade aggression. In the present study, we carry out a systematic study to test how common such chemical deception is across a group of 22 arthropods that are associated with red wood ants ( Formica rufa group). In contrast to the examples of chemical mimicry documented in some highly specialized parasites in previous studies, we find that most of the rather unspecialized red wood ant associates surveyed did not use mimicry of the cuticular hydrocarbon recognition cues to evade host detection. Instead, we found that myrmecophiles with lower cuticular hydrocarbon concentrations provoked less host aggression. Therefore, some myrmecophiles with low hydrocarbon concentrations appear to evade host detection via a strategy known as chemical insignificance. Others showed no chemical disguise at all and, instead, relied on behavioral adaptations such as particular defense or evasion tactics, in order to evade host aggression. Overall, this study indicates that unspecialized myrmecophiles do not require the matching of host recognition cues and advanced strategies of chemical mimicry, but can integrate in a hostile ant nest via either chemical insignificance or specific behavioral adaptations. [ABSTRACT FROM AUTHOR]

Ceropegia L. (Apocynaceae, Asclepiadoideae) comprises more than 200 species, all characterized by complex pitfall flowers. The deceptive flowers are myiophilous and pollinated predominantly by small flies from different families. It has been suggested that floral scent cues, that mimic food sources or oviposition sites, play an important role for attraction of target fly pollinators, and, together with morphological flower traits, explain the high functional specialization in terms of pollination by specific taxa. However, apart from two Ceropegia species, the floral scent composition and the mimicry strategies in this genus are unexplored. We tested for associations between floral scent and insect visitor and pollinator assemblages of 14 Ceropegia species. We also used nrDNA and chloroplast DNA markers to calculate a Maximum Likelihood tree and test for phylogenetic signal in scent chemistry and flower visitors/pollinators. The observed pollinators belonged to eight fly families, at least 18 genera, and 33 morphospecies, but each Ceropegia species was typically associated with only one or two pollinating fly families or genera. We detected a total of 317 floral volatiles, including aliphatic and aromatic components, terpenes, and various unknowns. Both flower visitor and pollinator patterns did not show an overall association with floral scent chemistry. There was phylogenetic signal in flower visiting fly families and fly pollinator assemblages, but not in flower visiting fly morphospecies and overall scent chemistry. We discuss that despite the not existing correlation between pollinator and scent patterns the highly specific pollination system in Ceropegia will be explained mainly by floral scent chemistry. [ABSTRACT FROM AUTHOR]

Ophrys flowers mimic sex pheromones of attractive females of their pollinators and attract males, which attempt to copulate with the flower and thereby pollinate it. Virgin females and orchid flowers are known to use the same chemical compounds in order to attract males. The composition of the sex pheromone and its floral analogue, however, vary between pollinator genera. Wasp-pollinated Ophrys species attract their pollinators by using polar hydroxy acids, whereas Andrena-pollinated species use a mixture of non-polar hydrocarbons. The phylogeny of Ophrys shows that its evolution was marked by episodes of rapid diversification coinciding with shifts to different pollinator groups: from wasps to Eucera and consequently to Andrena and other bees. To gain further insights, we studied pollinator attraction in O. leochroma in the context of intra- and inter-generic pollinator shifts, radiation, and diversification in the genus Ophrys. Our model species, O. leochroma, is pollinated by Eucera kullenbergi males and lies in the phylogeny between the wasp and Andrena-pollinated species; therefore, it is a remarkable point to understand pollinator shifts. We collected surface extracts of attractive E. kullenbergi females and labellum extracts of O. leochroma and analyzed them by using gas chromatography with electroantennographic detection (GC-EAD) and gas chromatography coupled with mass spectrometry (GC-MS). We also performed field bioassays. Our results show that O. leochroma mimics the sex pheromone of its pollinator's female by using aldehydes, alcohols, fatty acids, and non-polar compounds (hydrocarbons). Therefore, in terms of the chemistry of pollinator attraction, Eucera-pollinated Ophrys species might represent an intermediate stage between wasp- and Andrena-pollinated orchid species. [ABSTRACT FROM AUTHOR]

We present evidence that cerambycid species that are supposed mimics of vespid wasps also mimic their model's odor by producing spiroacetals, common constituents of vespid alarm pheromones. Adults of the North American cerambycids Megacyllene caryae (Gahan) and Megacyllene robiniae (Forster) are conspicuously patterned yellow and black, and are believed to be mimics of aculeate Hymenoptera, such as species of Vespula and Polistes. Adult males of M. caryae produce an aggregation-sex pheromone, but both sexes produce a pungent odor when handled, which has been assumed to be a defensive response. Headspace aerations of agitated females of M. caryae contained 16 compounds with mass spectra characteristic of spiroacetals of eight distinct chemical structures, with the dominant compound being (7 E,2 E)-7-ethyl-2-methyl-1,6-dioxaspiro[4.5]decane. Headspace samples of agitated males of M. caryae contained five of the same components, with the same dominant compound. Females of M. robiniae produced six different spiroacetals, one of which was not produced by M. caryae, (2 E,7 E)-2-ethyl-7-methyl-1,6-dioxaspiro[4.5]decane, and five that were shared with M. caryae, including the dominant (2 E,8 E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. The latter compound is the sole spiroacetal produced by both males and females of a South American cerambycid species, Callisphyris apicicornis (Fairmaire & Germain), which is also thought to be a wasp mimic. Preliminary work also identified spiroacetals of similar or identical structure released by vespid wasps that co-occur with the Megacyllene species. [ABSTRACT FROM AUTHOR]

Chemical mimicry is an effective strategy when signal receivers recognize and discriminate models by relying on chemical cues. Some aphid enemies mimic the cuticular chemicals of aphids through various means thus avoiding detection and attack by aphid-tending ants. However, because ants have been reported to learn the chemical signatures of aphids in order to distinguish the aphids, the efficacy of chemical mimicry is predicted to depend on the experience of the ants that had tended aphids. The present study tested this hypothesis using two predator species: larvae of the green lacewing Mallada desjardinsi, and larvae of the ladybeetle Scymnus posticalis. Lacewing larvae carry the carcasses of aphids on which they have preyed upon their backs, and these function via chemical camouflage to reduce the aggressiveness of aphid-tending ants toward the larvae. Ladybeetle larvae reportedly produce a covering of wax structures, and their chemicals appear to attenuate ant aggression. We examined whether the behavior of the ant Tetramorium tsushimae toward these predators changed depending on their aphid-tending experience. Ants moderated their aggressiveness toward both predators when they had previously tended aphids, indicating that chemical mimicry by both aphid predators is dependent on previous experience of the ants in tending aphids. Chemical mimicry by the predators of ant-tended aphids is therefore considered to exploit learning-dependent aphid recognition systems of ants. [ABSTRACT FROM AUTHOR]

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 cleptopar-asitic 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 cleptopar-asitic 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. [ABSTRACT FROM AUTHOR]

The parasitoid beetle Metoecus paradoxus frequently parasitizes colonies of the common wasp, Vespula vulgaris. It penetrates a host colony as a larva that attaches itself onto a foraging wasp's body and, once inside the nest, it feeds on a wasp larva inside a brood cell and then pupates. Avoiding detection by the wasp host is crucial when the beetle emerges. Here, we tested whether adult M. paradoxus beetles avoid detection by mimicking the cuticular hydrocarbon profile of their host. The beetles appear to be chemically adapted to their main host species, the common wasp, because they share more hydrocarbon compounds with it than they do with the related German wasp, V. germanica. In addition, aggression tests showed that adult beetles were attacked less by common wasp workers than by German wasp workers. Our results further indicated that the host-specific compounds were, at least partially, produced through recycling of the prey's hydrocarbons, and were not acquired through contact with the adult host. Moreover, the chemical profile of the beetles shows overproduction of the wasp queen pheromone, nonacosane (n-C), suggesting that beetles might mimic the queen's pheromonal bouquet. [ABSTRACT FROM AUTHOR]

Floral nectar often contains chemicals that are deterrent to pollinators, presenting potential challenges to outcrossing plant species. Plants may be able to co-opt pollinator chemical signals to mitigate the negative effects of nectar deterrent compounds on pollination services. We found that buckwheat ( Fagopyrum esculentum) and Mexican sunflower ( Tithonia diversifolia) produce nectar with abundant phenolics, including three components of the Apis honeybee queen mandibular pheromone (QMP). In addition, these nectars contain a non-pheromonal phenolic, chlorogenic acid (CA), which was toxic to honeybees, and T. diversifolia nectar also contained isochlorogenic acid (IA). Fresh nectar or solutions containing nectar phenolics reduced Apis individual feeding compared to sucrose solutions. However, freely foraging bees preferred solutions with QMP components to control solutions, and QMP components over-rode or reversed avoidance of CA and IA. Furthermore, prior exposure to the presence or just the odor of QMP components removed the deterrent effects of CA and IA. By mimicking the honey bee pheromone blend, nectar may maintain pollinator attraction in spite of deterrent nectar compounds. [ABSTRACT FROM AUTHOR]

The author discusses the semiochemical bases of Aristolochia rotunda (A. rotunda) plant, true bugs (Miridae), and the plant's pollinators' interaction. The author mentions that the interaction describe a pollination system called kleptomyiophily wherein pollinators were attracted to a compound released by A. rotunda flowers that mimics Miridae insect being killed.

Pollination of several angiosperms is based on deceit. In such systems, the flowers advertise a reward that ultimately is not provided. We report on a previously unknown pollination/mimicry system discovered in deceptive Aristolochia rotunda (Aristolochiaceae)., Pollinators were collected in the natural habitat and identified. Flower scent and the volatiles of insects (models) potentially mimicked were analyzed by chemical analytical techniques. Electrophysiological and behavioral tests on the pollinators identified the components that mediate the plant-pollinator interaction and revealed the model of the mimicry system., The main pollinators of A. rotunda were female Chloropidae. They are food thieves that feed on secretions of true bugs (Miridae) while these are eaten by arthropod predators. Freshly killed mirids and Aristolochia flowers released the same scent components that chloropids use to find their food sources. Aristolochia exploits these components to deceive their chloropid pollinators., Aristolochia and other trap flowers were believed to lure saprophilous flies and mimic brood sites of pollinators. We demonstrate for A. rotunda, and hypothesize for other deceptive angiosperms, the evolution of a different, kleptomyiophilous pollination strategy. It involves scent mimicry and the exploitation of kleptoparasitic flies as pollinators. Our findings suggest a reconsideration of plants assumed to show sapromyiophilous pollination. [ABSTRACT FROM AUTHOR]

Phengaris (Maculinea) butterflies are social parasites of Myrmica ant colonies. Larvae of the parasite are adopted by the ant workers into the colonies. Apparently, chemical signals are used by Phengaris nausithous Bergsträsser larvae to mimic those of the host brood to be recognized by the ants. In the present study, chemical extracts of ant brood and butterfly larvae using four different solvents are tested in behavioural choice assays in search of compounds involved in the adoption process. Tetracosane is the main shared compound in all brood extracts of Myrmica rubra L. and in all larvae of P. nausithous. The attractiveness of tetracosane for M. rubra workers is confirmed by testing synthetic tetracosane in behavioural choice assays, suggesting that the adoption ritual may be initiated by tetracosane. [ABSTRACT FROM AUTHOR]

Ants attack and exclude natural enemies of aphids in ant-aphid mutualisms. However, larvae of the green lacewing, Mallada desjardinsi, prey on the cowpea aphid, Aphis craccivora, without exclusion by aphid-tending ants. Lacewing larvae are protected from ants by carrying aphid carcasses on their backs. Here, we tested whether cuticular hydrocarbons (CHCs) of aphid carcasses affected the aggressiveness of aphid-tending ants. Aphid carcasses were washed with n-hexane to remove lipids. Lacewing larvae with washed aphid carcasses were attacked by aphid-tending ants more frequently than those with untreated aphid carcasses. We measured the aggressiveness of aphid-tending ants to lacewing larvae that were either carrying a piece of cotton wool (a dummy aphid carcass) treated with CHCs from aphids or lacewing larvae, or carrying aphid carcasses. The rates of attack by ants on lacewing larvae carrying CHCs of aphids or aphid carcasses were lower than that of attack on lacewing larvae with conspecific CHCs. Chemical analysis by gas chromatography/mass spectrometry showed similarity of CHCs between aphids and aphid carcasses. These results suggest that aphid carcasses on the backs of lacewing larvae function via chemical camouflage to limit attacks by aphid-tending ants. [ABSTRACT FROM AUTHOR]

Caterpillars of the parasitic lycaenid butterfly are often adopted by host ants. It has been proposed that this adoption occurs because the caterpillars mimic the cuticular hydrocarbons of the host ant. This study aimed to examine whether caterpillars of the Japanese lycaenid butterfly Niphanda fusca induce adoption by mimicking their host ant Camponotus japonicus. Behavioral observations conducted in the laboratory showed that most second-instar caterpillars were not adopted, whereas most third-instar caterpillars were successfully adopted by host workers. A chemical comparison detected no characteristic differences in the cuticular hydrocarbon profiles between second- and third-instar caterpillars. However, morphological features of the caterpillars differed between the second and third instars; third-instar caterpillars developed exocrine glands (ant organs) such as tentacle organs and a dorsal nectary organ. These results suggest that multiple chemical signatures, not only cuticular hydrocarbons, may be important for invasion of the host ant nest. [ABSTRACT FROM AUTHOR]

Abstract: Thorictus beetles of the Dermestidae are obligate myrmecophiles. To understand how these beetles are integrated into and tolerated by their host colonies, the cuticular hydrocarbon profiles of different species of the Thorictus castaneus group that are generally associated with Cataglyphis were examined. The beetles are characterized by small amounts of cuticular hydrocarbons, which render them partly chemically “insignificant”. They also have the same cuticular hydrocarbon profiles as their hosts and thus likely use chemical mimicry to evade worker hostility but, like slaves in slave-maker species, they maintain some partial chemical identity. Thorictus martinezi from Burkina Faso were immediately adopted by conspecific colonies of their host, Cataglyphis sp. aff. bicolor, but were never adopted by colonies of other species (i.e. Cataglyphis viatica and Formica selysi). Thorictus buigasi from Morocco also mimicked the chemical profile of its host, C. viatica, but, in contrast to T. martinezi, individuals were adopted by colonies of Cataglyphis velox from Spain. This result can be explained by the similarity between the hydrocarbon profiles of C. viatica and C. velox, which may facilitate adoptions. T. buigasi beetles remained in Formica selysi colonies for some time but were ultimately rejected, probably due to their very different hydrocarbon profiles. In contrast, they were sometimes adopted by Camponotus herculeanus colonies and eventually chemically matched their new hosts, probably by passive camouflage. These data suggest that Thorictus of castaneus group myrmecophily is the result of coevolution with Cataglyphis hosts and that the mimicry is plastic, such that beetles can live with different hosts if the hosts show very limited CHC differences. [Copyright &y& Elsevier]

Camouflage strategies are common in insect social parasites. Being accepted into an alien colony as a dominant nestmate favours behavioural and morphological adaptations to mimic a specific odour. In Polistes social parasites, abdominal tegumental glands are involved in this camouflage strategy. These glands secreting cuticular hydrocarbons are connected with a modified cuticular area of the last gastral sternite of female wasps, named Van der Vecht's organ, whose secretion is involved in rank and dominance recognition. The size of this exocrine area has been demonstrated to be under selective pressure in Polistes, as a response to an efficient dominance recognition. Because chemical and behavioural integration differs between parasitic species, we carried out a comparison of Van der Vecht's organ size between the three Polistes social parasites and their respective hosts. The parasites Polistes sulcifer and Polistes semenowi, capable of a rapid chemical mimicry and specialized to exploit a lowland host, also show an enlarged Van der Vecht's organ. Conversely, the parasite Polistes atrimandibularis, specialized on a mountain species and showing a slow chemical integration, has a smaller organ. The time available for the parasite to tune up its chemical mimicry, before the emergence of workers to be accepted as a dominant nestmate, appears to be the most important selective pressure acting on the size of this abdominal organ. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Aphid-tending ants protect aphids from natural enemies and collect honeydew secreted by the aphids. However, ants also often prey on the aphids they attend. Aphids, therefore, like social parasites of ants, may well have evolved chemical mimicry as an anti-predation strategy. In this study, we aimed to determine whether the aphid Stomaphis yanonis actively produces cuticular hydrocarbons (CHCs) that resemble those of the tending ant Lasius fuji. In the wild, ants put their CHCs on the aphids that they are tending, so in this study we analyzed 'ant-free' aphids. Mature aphids that exuviated in the absence of ant attendance had almost all of the hydrocarbon components that the ants' CHCs had. Moreover, hydrocarbons artificially applied to the aphids' body surface were lost by exuviation. Taken together, these findings indicate that mature aphids actively produced ant-like CHCs, and they constitute the first documentation of a chemical resemblance between aphids and ants in a specific aphid-ant association. [ABSTRACT FROM AUTHOR]

Pollination based on insect deception has been debated in the scientific community since it was first reported over two hundred years ago. A vast majority of deceptive syndromes occur within the orchid family. While many cheating flowers have been described and are well known, there are still many curious cases that need further investigation. One prime example of such a case is Cypripedium calceolus, known as European lady's slipper orchid. While the flower has been of interest to many prominent scientists for over a century, its pollination is still not fully understood. Both visual and olfactory cues seem to play an important role in pollinator attraction. In this study we focussed on the olfactory cues in order to explore their relationship (in future experiments) with floral visual cues, including the unique asymmetry of these flowers. Some of the plants' floral fragrances were used in Electroantennography experiments. Eleven chemical compounds were applied to the antennae of Bombus terrestris and Apis mellifera. Even though these species are not regular Visitors of C. calceolus, we were interested to see whether there were common principles in their responses to the flowers' scent that might justify extrapolating to other pollinator species such as sand bees that get trapped in these orchids and fly out of the flowers afterwards with pollen smeared on their body. The results show that while both species react similarly to most of the odours, some of the tested acetates induced a significantly greater reaction in B. terrestris antennae. These acetates play an important role in bumblebee pheromones, but their relevance for the natural pollinators of C. calceolus remains to be confirmed to see whether chemical mimicry by these flowers is deliberately employed to attract pollinators. [ABSTRACT FROM AUTHOR]

Social parasitism is widespread in many groups of social living hymenopteran species and has also evolved in the genus Bombus. Cuckoo bumblebees (subgenus Psithyrus) are obligate brood parasites in nests of other bumblebee species. After nest usurpation and the killing of the host queen, the parasite female has to control worker reproduction in order to accomplish and maintain reproductive dominance and to ensure her reproductive success. The aim of our study was to examine whether the generalist parasitic bumblebee Bombus bohemicus monopolizes and prevents worker reproduction by physical or chemical means and to identify possible odor compounds involved therein. We performed bioassays with callow workers of the host Bombus terrestris and have shown that B. bohemicus females are able to suppress host worker ovarian development, when these host workers are under the direct influence of the parasite female. Furthermore, by chemical analyses, we have demonstrated that the parasite females adjust to the odor profiles of their host queens in order to maintain the level of fertility signaling inside the host colony although the host queen is absent. We also found that host workers change their odor profile after nest usurpation by the parasite female and consequently, we suggest that the host and parasite are caught up in a chemical arms race. [ABSTRACT FROM AUTHOR]

Sexually deceptive orchids of the genus Ophrys attract male insects for pollination. Pollinator attraction is achieved by mimicking sex pheromones of virgin females of their pollinators, mostly bee species. In earlier investigations, we showed that the phylogenetically distinct Ophrys species O. chestermanii and O. normanii on Sardinia attract their pollinator, males of the cuckoo bumblebee B. vestalis, with the same bouquets of relatively polar volatile compounds. In this investigation, we studied the sex pheromone of virgin females of B. vestalis with the aim of identifying male-attracting compounds and of comparing them with labellum extracts of the two orchids, which were found to release male-attracting compounds in earlier investigations (Gögler et al. ). In bioassays, shock-frozen females, cuticle extracts and polar fractions of cuticle extracts of virgin females stimulated mating behaviour in the males. Using gas chromatography coupled with electroantennography (GC-EAD) and gas chromatography coupled with mass spectrometry (GC-MS), we detected in polar fractions of cuticle extracts of B. vestalis females the same electrophysiologically active compounds as in labellum extracts of both orchid species, including aldehydes, esters, fatty acids and alcohols. Since statistical comparisons of the relative proportions of esters showed strong similarities between virgin females and orchids, our results support the hypotheses that this highly specialized Ophrys-pollinator relationship represents another case of chemical mimicry and that esters play a key role in male attraction. [ABSTRACT FROM AUTHOR]

Insect social life is governed by chemicals. A great number of studies have demonstrated that the blend of hydrocarbons present on the cuticle (CHCs) plays a pivotal role in intra- and inter-specific communication. It is not surprising, therefore, that social parasites, specialized in exploiting the costly parental care provided by host workers, exploit the host chemical communication system too. Throughout their life cycle, social parasites intercept and break this CHC-based code. Recently, however, several polar compounds (mainly peptides) have been found in addition to CHCs both on the cuticle and on the comb surface of social insects, and their semiochemical role has been demonstrated in some circumstances. In the present study, we used the paper wasp social parasite-host system Polistes sulcifer (Zimmerman)-Polistes dominulus (Christ) to evaluate the relative importance of the CHC5 and polar compounds in two different steps of the host exploitation process: host nest detection by the pre-usurping parasite and parasite chemical integration into the host colony. After separating the polar and apolar fractions of the host nest as well as those of pre- and post-usurpation parasites, we carried out laboratory assays based on the binary choice model. Our results show that nest polar compounds neither are used by the parasite to detect the host's nest nor play a role in parasite chemical integration into the host colony. In contrast, we demonstrate that CHCs are fundamental in both steps, thus confirming their primary role in social insect life and consequently in social parasite-host interactions. [ABSTRACT FROM AUTHOR]