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Chemical cues and signals, especially in insects, play a pivotal role in mediating interactions between individuals. Past studies have largely focused on adult semiochemicals and have neglected those of juvenile stages. Especially in the context of parental care, the larval odor might have a profound impact on parenting behavior, guiding parents in how much resources they should allocate to the different developmental stages. However, whether ontogenetic changes occur in subsocial species and whether larval-emitted scents influence parent-offspring interactions is largely unknown. Using 3 different sampling techniques, we analyzed the cuticular and VOC profile of the 3 larval instars of the burying beetle Nicrophorus vespilloides , which is known for its elaborate parental care. We found distinct differences in the cuticular and VOC profiles across the 3 larval stages. Second-instar larvae, which receive more frequent feedings from parents than the other larval stages, released greater amounts of acetophenone, methyl geranate, and octanoic acid isopropyl ester than the first and third instar. Additionally, using a newly developed bioassay with automated video tracking, we found that adding the odor of second-instar larvae to first-instar larvae increased the number of maternal feeding trips. Our results suggest that the odor produced by larvae plays an important role in mediating parent-offspring interactions. Given these findings, burying beetles might emerge as a promising candidate for identifying a potential begging pheromone., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology.)

The parasitoid wasp Trichopria drosophilae is promising as a biocontrol agent for controlling the ubiquitous pest Drosophila suzukii (Matsumura). Crucial for the successful implementation of any biocontrol agent is a high parasitisation rate by the parasitoid. Most studies investigating the parasitisation rate of D. suzukii pupae have focused on parasitisation in the fruit or in a petri dish. However, the predominant pupation site of D. suzukii in the field is the soil. Unfortunately, little is known on how well parasitoid wasps can detect and parasitise pupae of D. suzukii buried in the soil. Therefore, we conducted soil parasitisation experiments of T. drosophilae on D. suzukii pupae using two pupation depths in three different soil types (loamy sand, loam, and clay). In all three soil types, we found generally low D. suzukii pupae parasitisation rate by T. drosophilae, independent of the pupation depth. The pupation behaviour of D. suzukii and the parasitisation behaviour of T. drosophilae are discussed in detail. For pest control in most soil types, our results mean that the number of D. suzukii larvae pupating in the soil should be reduced, e.g., by adding a layer of sandy soil or covering the soil with plastic mulch. This might increase the probability of success when using T. drosophilae as a biocontrol agent., (© 2022. The Author(s).)

AbstractMicrobial volatiles provide essential information for animals, which compete to detect, respond to, and perhaps control this information. Burying beetle parents have the opportunity to influence microbially derived semiochemicals, because they monopolize a small carcass for their family, repairing feeding holes and applying exudates that alter the microbial community. To study adaptive manipulation of microbial cues, we integrated mechanistic and functional approaches. We contrasted gas chromatography-mass spectrometry (GC-MS) volatile profiles from carcasses that were or were not prepared by a resident pair of Nicrophorus orbicollis . Methyl thiocyanate (MeSCN), the primary attractant for burying beetles seeking a fresh carcass, was reduced 20-fold by carcass preparation, while dimethyl trisulfide (DMTS), which deters breeding beetles, was increased 20-fold. These results suggest that parental care serves to make previously public information more private (crypsis, MeSCN) and to disinform rivals with a deterrent (DMTS). Functional tests in the field demonstrated that carcass preparation reduced discovery and use by congeners (threefold) as well as by dipteran rivals. Because microbes and their chemicals influence nearly every aspect of animal ecology, animal manipulation of microbial cues may be as widespread as manipulation of their own signals.

Controlling the cosmopolitan pest Drosophila suzukii (spotted wing drosophila) is a challenge for fruit growers. A promising agent for biological control of that pest are parasitoid wasps. Especially the widespread pupal parasitoid Trichopria drosophilae had shown the ability to parasitise the pest fly. However, as a biocontrol agent, parasitoids can only be effective when they prefer the pest to other insects. Until now studies have been inconsistent concerning the preference of T. drosophilae for D. suzukii and whether the preference depends on pupal volume. To clarify this inconsistency, we used video recordings of parasitisation experiments with a set up to observe the direct host preference of the parasitoid. Additionally, the volume of each host pupa was measured. We found significant preference of T. drosophilae for D. suzukii pupae independent of the pupal size and of the host species the wasps were reared on. The article also discusses the sex ratio and the success of the parasitoid in the different pupae characteristics.

Deciphering the processes driving the evolution of the diverse pheromone-mediated chemical communication system of insects is a fascinating and challenging task. Understanding how pheromones have arisen has been supported by studies with the model organism Leptopilina heterotoma, a parasitoid wasp whose defensive compound (-)-iridomyrmecin also evolved as a component of the female sex pheromone and as a cue to avoid competition with other females during host search. To understand how compounds can evolve from being non-communicative to having a communicative function and to shed light on the evolution of the multi-functional use of iridomyrmecin in the genus Leptopilina, the chemical communication of two additional species, L. ryukyuensis and L. japonica, was studied. We demonstrate that in both species a species-specific mixture of iridoids is produced and emitted by wasps upon being attacked, consistent with their putative role as defensive compounds. In L. ryukyuensis these iridoids are also used by females to avoid host patches already exploited by other conspecific females. However, females of L. japonica do not avoid the odor of conspecific females during host search. We also show that the sex pheromone of female L. ryukyuensis consists of cuticular hydrocarbons (CHCs), as males showed strong courtship behavior (wing fanning) towards these compounds, but not towards the iridoid compounds. In contrast, males of L. japonica prefer their females' iridoids but CHCs also elicit some courtship behavior. The use of iridoid compounds as defensive allomones seems to be common in the genus Leptopilina, while their communicative functions appear to have evolved in a species-specific manner.

Beetles have evolved diverse strategies to cope with environmental challenges. Although parents of the vast majority of beetle species do not take care of their offspring, there are some species, in which parents provide elaborate post-hatching care and remain temporarily associated with their offspring to defend them from competitors or to provision them with food. Usually, socially induced reproductive "control" is a core feature of eusocial societies, but here we highlight that already in small family groups, socially induced reproductive regulation can play a fundamental role. By discussing the family life of burying beetles, we illustrate the mechanisms behind such a reproductive "control" and show that - similar to eusocial insects - pheromones can be an important regulating factor. However, apart from burying beetles, our knowledge of pheromones or other signals mediating reproductive regulation is surprisingly rudimentary for social beetles. More data are required to broaden our currently patchy picture.

Lipid synthesis can have a major effect on survival and reproduction, yet most insect parasitoids fail to synthesize lipids. For parasitic wasps in the genus Leptopilina, however , studies have suggested that there is intraspecific variation in the ability for lipid synthesis. These studies were performed on only few populations, and a large-scale investigation of both lipogenic ability and population genetic structure is now needed. Here, we first examined lipogenic ability of nine Leptopilina heterotom a populations collected in 2013 and found that five of nine populations synthesized lipids. The 2013 populations could not be used to determine genetic structure; hence, we obtained another 20 populations in 2016 that were tested for lipogenic ability. Thirteen of 20 populations (all Leptopilina heterotom a) were then used to determine the level of genetic differentiation (i.e., haplotype and nucleotide diversity) by sequencing neutral mitochondrial ( COI ) and nuclear (ITS2) markers. None of the 2016 populations synthesized lipids, and no genetic differentiation was found. Our results did reveal a nearly twofold increase in mean wasp lipid content at emergence in populations obtained in 2016 compared to 2013. We propose that our results can be explained by plasticity in lipid synthesis, where lipogenic ability is determined by environmental factors, such as developmental temperature and/or the amount of lipids carried over from the host.

According to current evolutionary theory, insect pheromones can originate from extant precursor compounds being selected for information transfer. This is exemplified by females of the parasitoid wasp Leptopilina heterotoma whose defensive secretion consisting mainly of (-)-iridomyrmecin has evolved secondary functions as cue to avoid other females during host search and as female sex pheromone. To promote our understanding of pheromone evolution from defensive secretions we studied the chemical ecology of Leptopilina clavipes. We show here that L. clavipes also produces a defensive secretion that contains (-)-iridomyrmecin as major component and that females use it to detect and avoid host patches occupied by other females. However, the female sex pheromone of L. clavipes consists solely of cuticular hydrocarbons (CHCs) and males did not respond to female CHCs if presented in combination with the defensive secretion containing (-)-iridomyrmecin. This is in contrast to other species of Leptopilina, in which the iridoid compounds have no inhibiting effect or even function as sex pheromone triggering courtship behaviour. This indicates that Leptopilina species differ in the cost-benefit ratio for males searching for females, which might explain the strong divergence in the composition of the sex pheromone in the genus.

Effective parental care requires recognition and communication processes. Whereas chemical communication has been studied intensively in eusocial organisms, in which the workers (siblings) predominantly provide brood care, insect groups in which parents engage in care have been largely neglected. However, the study of communication in insect families might complement and enhance our understanding not only of the evolution of signaling process involved in social insects, but also of those involved in vertebrate families. In this review, we synthesize the existing information about the pheromones and chemical cues that regulate and affect insect parental care and family life. We will present research dealing with pre-hatching as well as post-hatching parental care and cover interactions between parents and offspring, between male and female parents, and among siblings., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Communication via chemical signals, that is, pheromones, is of pivotal importance for most insects. According to current evolutionary theory, insect pheromones originated either from extant precursor compounds being selected for information transfer or by the pheromone components exploiting a pre-existing sensory bias in the receiver. Here, we review the available experimental evidence for both hypotheses. Existing data indicate that most insect pheromones evolved from precursor compounds that were emitted as metabolic by-products or that previously had other non-communicative functions. Many studies have investigated cuticular hydrocarbons that have evolved a communicative function, although examples of pheromones exist that have arisen from defensive secretions, hormones or dietary compounds. We summarize and discuss the selective pressures shaping the pheromone during signal evolution., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Burying beetles have fascinated scientists for centuries due to their elaborate form of biparental care that includes the burial and defense of a vertebrate carcass, as well as the subsequent feeding of the larvae. However, besides extensive research on burying beetles, one fundamental question has yet to be answered: what cues do males use to discriminate between the sexes? Here, we show in the burying beetle Nicrophorus vespilloides that cuticular lipids trigger male mating behavior. Previous chemical analyses have revealed sex differences in cuticular hydrocarbon (CHC) composition; however, in the current study, fractionated-guided bioassay showed that cuticular lipids, other than CHCs, elicit copulation. Chemical analyses of the behaviorally active fraction revealed 17 compounds, mainly aldehydes and fatty acid esters, with small quantitative but no qualitative differences between the sexes. Supplementation of males with hexadecanal, the compound contributing most to the statistical separation of the chemical profiles of males and females, did not trigger copulation attempts by males. Therefore, a possible explanation is that the whole profile of polar lipids mediates sex recognition in N. vespilloides.

Chemical communication by the parasitoid wasp Leptopilina heterotoma is based largely on (-)-iridomyrmecin. The female wasps use (-)-iridomyrmecin as a defensive allomone, a chemical cue to avoid competition with con- and heterospecific females, and as a major component of their sex pheromone to attract males. Males of L. heterotoma produce (+)-isoiridomyrmecin, which is also used for chemical defense. In this study we show that females and males of L. heterotoma produce the iridomyrmecins in a pair of mandibular glands. Each gland consists of a secretory part composed of class 3 gland cells and their accompanying duct cells, as well as a reservoir bordered by a thin intima. The gland discharges between the mandible base and the clypeus. Males have considerably smaller glands than females, which corresponds to the lower amount of iridomyrmecins produced by males. Chemical analyses of the mandibular gland contents showed that the gland of females contained mainly (-)-iridomyrmecin, as well as low amounts of the other previously described iridoid pheromone compounds, while the glands of males contained only (+)-isoiridomyrmecin. The morphology and sizes of the mandibular glands of males and females of L. heterotoma have evolved to the multi-functional use of iridomyrmecin., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The high energetic demand of parental care requires parents to direct their resources towards the support of existing offspring rather than investing into the production of additional young. However, how such a resource flow is channelled appropriately is poorly understood. In this study, we provide the first comprehensive analysis of the physiological mechanisms coordinating parental and mating effort in an insect exhibiting biparental care. We show a hormone-mediated infertility in female burying beetles during the time the current offspring is needy and report that this temporary infertility is communicated via a pheromone to the male partner, where it inhibits copulation. A shared pathway of hormone and pheromone system ensures the reliability of the anti-aphrodisiac. Female infertility and male sexual abstinence provide for the concerted investment of parental resources into the existing developing young. Our study thus contributes to our deeper understanding of the mechanisms underlying adaptive parental decisions.

Detecting danger is one of the foremost tasks for a neural system. Larval parasitoids constitute clear danger to Drosophila, as up to 80% of fly larvae become parasitized in nature. We show that Drosophila melanogaster larvae and adults avoid sites smelling of the main parasitoid enemies, Leptopilina wasps. This avoidance is mediated via a highly specific olfactory sensory neuron (OSN) type. While the larval OSN expresses the olfactory receptor Or49a and is tuned to the Leptopilina odor iridomyrmecin, the adult expresses both Or49a and Or85f and in addition detects the wasp odors actinidine and nepetalactol. The information is transferred via projection neurons to a specific part of the lateral horn known to be involved in mediating avoidance. Drosophila has thus developed a dedicated circuit to detect a life-threatening enemy based on the smell of its semiochemicals. Such an enemy-detecting olfactory circuit has earlier only been characterized in mice and nematodes.

Many insects use chemical defence mechanisms to defend themselves against predators. However, defensive secretions are costly to produce and should thus only be used in cases of real danger. This would require that insects are able to discriminate between predators to adjust their chemical defence. Here, we show that females of the parasitoid wasp Leptopilina heterotoma adjust the intensity of their chemical defence to differently sized predators. If attacked by Myrmica ants, the females always released their defensive secretion, which consists mainly of (-)-iridomyrmecin. However, if attacked by smaller Cardiocondyla ants, most females did not release any defensive spray, irrespective of the duration of the ant's aggression. When in contact with non-aggressive Nasonia wasps, the females of L. heterotoma did not release any defensive secretion. Our data show that females of L. heterotoma are able to discriminate between two predators and suggest that a predator of a certain size or strength is necessary to trigger the chemical defence mechanism of L. heterotoma.

Solvent extraction of bioactive molecules from glands, tissues, or whole organisms is a common first step in chemoecological studies. Co-extraction of a surplus of high boiling materials such as triacylglycerides (TAGs) and other lipids with higher molecular weight might hamper the identification of volatile or medium-volatile semiochemicals by high resolution chromatographic and spectroscopic techniques. Therefore, effective clean-up procedures are needed to separate potential semiochemicals from the accompanying materials. Size exclusion high performance liquid chromatography (SE-HPLC), a technique often disregarded by chemoecologists, has proved to be a rapid and efficient clean-up method for complex crude extracts. We demonstrated that TAGs can be baseline separated from typical semiochemicals within less than 10 min on a porous gel stationary phase based on highly cross-linked polystyrene/divinylbenzene. We applied the method as a rapid one-step clean-up procedure for the analysis of juvenile hormone III in insect hemolymph by gas chromatography-mass spectrometry. We furthermore introduced some recent application examples on insect pheromones to demonstrate that SE-HPLC is not only an effective method for the purification of crude extracts, but can as well be used as a first fractionation step for the bioassay-guided identification of behavior modifying natural products. SE-HPLC can be well operated with low-boiling solvents such as dichloromethane, and results in fraction volumes of typically less than one ml, which decreases the danger of losing volatile analytes during subsequent concentration steps.

Male antennal aphrodisiac pheromones have been suggested to elicit female receptiveness in several parasitic Hymenoptera, including Leptopilina boulardi. None of the proposed pheromones, however, has been fully identified to date. It is also unknown whether these antennal pheromones are species specific, because the species specificity of mate recognition and courtship elicitation in Leptopilina prevented such experiments. In this study we present an experimental design that allows the investigation of the species specificity of the putative male aphrodisiac pheromone of L. heterotoma, L. boulardi, and L. victoriae. This is achieved by chemical manipulation of the odour profile of heterospecific females, so that males perceive them as conspecifics and show antennal courtship behaviour. Males courted the manipulated heterospecific females and antennal contact between the male and the female was observed. However, males elicited receptiveness only in conspecific females, never in the manipulated heterospecific females. Chemical analysis showed the presence of species specific unsaturated hydrocarbons on the antennae of males. Only trace amounts of these hydrocarbons are found on the antennae of females. Our results are an important step towards the understanding and identification of antennal pheromones of parasitic wasps.

Adaptation requires genetic variation, but founder populations are generally genetically depleted. Here we sequence two populations of an inbred ant that diverge in phenotype to determine how variability is generated. Cardiocondyla obscurior has the smallest of the sequenced ant genomes and its structure suggests a fundamental role of transposable elements (TEs) in adaptive evolution. Accumulations of TEs (TE islands) comprising 7.18% of the genome evolve faster than other regions with regard to single-nucleotide variants, gene/exon duplications and deletions and gene homology. A non-random distribution of gene families, larvae/adult specific gene expression and signs of differential methylation in TE islands indicate intragenomic differences in regulation, evolutionary rates and coalescent effective population size. Our study reveals a tripartite interplay between TEs, life history and adaptation in an invasive species.

Chemical communication is the most ancient and widespread form of communication. Yet we are only beginning to grasp the complexity of chemical signals and the role they play in sexual selection. Focusing on insects, we review here the recent progress in the field of olfactory-based sexual selection. We will show that there is mounting empirical evidence that sexual selection affects the evolution of chemical traits, but form and strength of selection differ between species. Studies indicate that some chemical signals are expressed in relation to an individual's condition and depend, for example, on age, immunocompetence, fertility, body size or degree of inbreeding. Males or females might benefit by choosing based on those traits, gaining resources or "good genes". Other chemical traits appear to reliably reflect an individual's underlying genotype and are suitable to choose a mating partner that matches best the own genotype.

Wasps of genus Asobara, a larval parasitoid of Drosophila, have become model organisms for the study of host-parasite interactions. However, little is known about the role of pheromones in locating mates and courtship behavior in this genus. In the present study, we aimed to identify the female courtship pheromone in Asobara tabida. The chemical compositions of solvent extracts from male and female wasps were analyzed by GC/MS. These extracts, fractions thereof, and synthetic pheromone candidates were tested for their activity in behavioral bioassays. The results demonstrate that the courtship pheromone of A. tabida is characterized by a remarkable chemical diversity. A multi-component blend of female-specific compounds including methyl 6-methylsalicylate (M6M), fatty alcohol acetates (FAAs), and cuticular hydrocarbons (CHCs) released male courtship behavior. Using a combinatory approach that included both purified natural products and synthetic analogs, it was shown that none of the three chemical classes alone was sufficient to release a full behavioral response in males. However, a blend of M6M and FAAs or combinations of one or both of these with female-derived CHCs resulted in wing-fanning responses by males comparable to those elicited by the crude extract of females. Thus, components from all three chemical classes contribute to the bioactivity of the pheromone, but none of the elements plays a key role or is irreplaceable. The fact that one of the FAAs, vaccenyl acetate, is also used as a kairomone by Asobara females to locate Drosophila hosts suggests that a pre-existing sensory responsiveness to vaccenyl acetate might have been involved in the evolution of the female sex pheromone in Asobara.

Cuticular hydrocarbons (CHCs) play an essential role in mate recognition in insects but the form and intensity of sexual selection on CHCs has only been evaluated in a handful of studies, and never in a natural population. We quantified sexual selection operating on CHCs in a wild population of sagebrush crickets, a species in which nuptial feeding by females imposes an unambiguous phenotypic marker on males. Multivariate selection analysis revealed a saddle-shaped fitness surface, suggesting a complex interplay between the total abundance of CHCs and specific CHC combinations in their influence on female choice. The fitness surface resulting from two axes of disruptive selection reflected a trade-off between short- and long-chained CHCs, suggesting that males may be sacrificing some level of desiccation resistance in favour of increased attractiveness. There was a significant correlation between male body size and total CHC abundance, suggesting that male CHCs provide females with a reliable cue for maximizing benefits obtained from males. Notwithstanding the conspicuousness of males' acoustic signals, our results suggest that selection imposed on males via female mating preferences may be far more complex than previously appreciated and operating in multiple sensory modalities.

The evolution of chemical communication and the origin of pheromones are among the most challenging issues in chemical ecology. Current theory predicts that chemical communication can arise from compounds primarily evolved for non-communicative purposes but experimental evidence showing a gradual evolution of non-informative compounds into cues and true signals is scarce. Here we report that females of the parasitic wasp Leptopilina heterotoma use the defensive compound (-)-iridomyrmecin as a semiochemical cue to avoid interference with con- and heterospecific competitors and as the main component of a species-specific sex pheromone. Although competition avoidance is mediated by (-)-iridomyrmecin alone, several structurally related minor compounds are necessary for reliable mate attraction and recognition. Our findings provide insights into the evolution of insect pheromones by demonstrating that the increasing specificity of chemical information is accompanied by an increasing complexity of the chemical messengers involved and the evolution of the chemosensory adaptations for their exploitation.

Chemical defense mechanisms are widespread among insects but have rarely been demonstrated in parasitoid wasps. Here, we show that the Drosophila parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) produces (-)-iridomyrmecin and (+)-isoiridomyrmecin in a cephalic gland, and that these chemicals have a highly repellent effect on ants. Stereoselective synthesis of 4 stereoisomers of iridomyrmecin allowed us to demonstrate that the repellent effect of iridomyrmecins depends on the stereochemistry. Potential food items impregnated with natural doses of (-)-iridomyrmecin were avoided by ants much longer than those impregnated with (+)-iridomyrmecin, (+)-isoiridomyrmecin, or (-)-isoiridomyrmecin, respectively. Quantitative headspace analyses revealed furthermore that females and males of L. heterotoma released iridomyrmecins in higher amounts when confronted with ants. This is the first time, that (-)-iridomyrmecin and (+)-isoiridomyrmecin are reported as natural products. Females synthesize more iridomyrmecins than males, and the most active (-)-iridomyrmecin is produced by females only. We, therefore, hypothesize that this defense mechanism is used mainly by female wasps when foraging for Drosophila larvae on rotten fruits, but also may protect male wasps during dispersal.

Sexually deceptive orchids mimic females of their pollinator species to attract male insects for pollination. Pollination by sexual deception has independently evolved in European, Australian, South African, and South American orchid taxa. Reproductive isolation is mainly based on pre-mating isolation barriers, the specific attraction of males of a single pollinator species, mostly bees, by mimicking the female species-specific sex-pheromone. However, in rare cases post-mating barriers have been found. Sexually deceptive orchids are ideal candidates for studies of sympatric speciation, because key adaptive traits such as the pollinator-attracting scent are associated with their reproductive success and with pre-mating isolation. During the last two decades several investigations studied processes of ecological speciation in sexually deceptive orchids of Europe and Australia. Using various methods like behavioural experiments, chemical, electrophysiological, and population-genetic analyses it was shown that minor changes in floral odour bouquets might be the driving force for pollinator shifts and speciation events. New pollinators act as an isolation barrier towards other sympatrically occurring species. Hybridization occurs because of similar odour bouquets of species and the overlap of flowering periods. Hybrid speciation can also lead to the displacement of species by the hybrid population, if its reproductive success is higher than that in the parental species., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Most insects are dependent on chemical communication for activities such as mate finding or host location. Several plants, and especially orchids, mimic insect semiochemicals to attract insects for unrewarded pollination. Here, we present a new case of pheromone mimicry found in the terrestrial orchid Epipactis veratrifolia. Flowers are visited and pollinated by several species of aphidophagous hoverflies, the females of which also often lay eggs in the flowers. The oviposition behaviour of these hoverflies is mainly guided by aphid-derived kairomones. We show that the flowers produce α- and β-pinene, β-myrcene and β-phellandrene, and that these compounds attract and induce oviposition behaviour in female hoverflies. This floral odour profile is remarkably similar to the alarm pheromone released by several aphid species, such as Megoura viciae. We therefore suggest that E. veratrifolia mimics aphid alarm pheromones to attract hoverflies for pollination; this is the first time, to our knowledge, that such a case of mimicry has been demonstrated.

In deceptive pollination, insects are bamboozled into performing nonrewarded pollination. A prerequisite for the evolutionary stability in such systems is that the plants manage to generate a perfect sensory impression of a desirable object in the insect nervous system [1]. The study of these plants can provide important insights into sensory preference of their visiting insects. Here, we present the first description of a deceptive pollination system that specifically targets drosophilid flies. We show that the examined plant (Arum palaestinum) accomplishes its deception through olfactory mimicry of fermentation, a strategy that represents a novel pollination syndrome. The lily odor is composed of volatiles characteristic of yeast, and produces in Drosophila melanogaster an antennal detection pattern similar to that elicited by a range of fermentation products. By functional imaging, we show that the lily odors target a specific subset of odorant receptors (ORs), which include the most conserved OR genes in the drosophilid olfactome. Furthermore, seven of eight visiting drosophilid species show a congruent olfactory response pattern to the lily, in spite of comprising species pairs separated by ∼40 million years [2], showing that the lily targets a basal function of the fly nose, shared by species with similar ecological preference., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species by mimicking the female species-specific sex pheromone. Changes in the odor composition can lead to hybridization and speciation by the attraction of a new pollinator that acts as an isolation barrier toward other sympatrically occurring Ophrys species. On Sardinia, we investigated the evolutionary origin of two sympatrically occurring endemic species, Ophrys chestermanii and O. normanii, which are both pollinated by males of the cuckoo bumblebee Bombus vestalis. Chemical and electrophysiological analyses of floral scent and genetic analyses with amplified fragment length polymorphisms and plastid-markers clearly showed that O. normanii is neither a hybrid nor a hybrid species. The two species evolved from different ancestors, viz. O. normanii from O. tenthredinifera and O. chestermanii from O. annae, and converged to the same pollinator attracted by the same bouquet of polar compounds. In spite of sympatry, pollinator sharing and overlapping blooming periods, no evidence has been obtained for gene flow between O. chestermanii and O. normanii indicating an unusual case among sexually deceptive orchids in which postmating rather than premating reproductive isolation mechanisms strongly prevent interspecific gene flow.

In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species, mostly bees, by mimicking the female sex pheromone of this species. Changes in the floral odor can lead to hybridization, introgression, and possibly speciation. We investigated hybrid swarms of O. lupercalis and O. iricolor on Sardinia using behavioral, electrophysiological (GC-EAD), chemical, morphological, and genetic methods (AFLPs). In behavioral experiments, approximately 20% of the flowers from both species and hybrids were attractive to the "wrong" or both pollinator species. Analysis of the EAD-active hydrocarbons in the floral odor showed an overlap in the two species, whereby hybrid individuals could not be separated from O. iricolor. The genetic analysis confirmed the hybridization of the species. Plants of O. iricolor and hybrids are genetically indistinguishable and form an O. iricolor × lupercalis hybrid population. Remaining plants of O. lupercalis will possibly be displaced by the O. iricolor × lupercalis hybrid population in the future. Our study showed that in deceptive orchids, variation in the pollinator attracting cues, in this case, scent, can be the first step for speciation and at the same time cause the displacement of a species.