Identification and Composition of Clasper Scent Gland Components of the Butterfly Heliconius erato and Its Relation to Mimicry

Complexity of Chemical Emissions Increases Concurrently with Sexual Maturity in Heliconius Butterflies

Pheromone communication is widespread among animals. Since it is often involved in mate choice, pheromone production is often tightly controlled. Although male sex pheromones (MSPs) and anti-aphrodisiacs have been studied in some Heliconius butterfly species, little is known about the factors affecting their production and release in these long-lived butterflies. Here, we investigate the effect of post-eclosion age on chemical blends from pheromone-emitting tissues in Heliconius atthis and Heliconius charithonia, exhibiting respectively free-mating and pupal-mating strategies that are hypothesised to differently affect the timing of their pheromone emissions. We focus on two different tissues: the wing androconia, responsible for MSPs used in courtship, and the genital tip, the production site for anti-aphrodisiac pheromones that affect post-mating behaviour. Gas chromatography-mass spectrometric analysis of tissue extracts from virgin males and females of both species from day 0 to 8 post-eclosion demonstrates the following. Some ubiquitous fatty acid precursors are already detectable at day 0. The complexity of the chemical blends increases with age regardless of tissue or sex. No obvious difference in the time course of blend production was evident between the two species, but female tissues in H. charithonia were more affected by age than in H. atthis. We suggest that compounds unique to male androconia and genitals and whose amount increases with age are potential candidates for future investigation into their roles as pheromones. While this analysis revealed some of the complexity in Heliconius chemical ecology, the effects of other factors, such as the time of day, remain unknown.

Nitidane: An Irregular Prenylated Diterpene from the Cuticle of the Springtail Heteromurus nitidus

Collembola are closely related to insects, but our knowledge of their often unique chemistry is limited. Here we report the identification of the epicuticular lipid nitidane, representing a novel class of epicuticular lipids. Nitidane (4) is an irregular terpene consisting of seven isoprene units, made up of a diterpene core that is modified by a geranyl moiety that is itself prenylated. The observed [46+(22+11)1]-terpene structure has not been reported before.

Variation of Clasper Scent Gland Composition of Heliconius Butterflies from a Biodiversity Hotspot

Male Heliconius butterflies possess two pheromone emitting structures, wing androconia and abdominal clasper scent glands. The composition of the clasper scent gland of males of 17 Heliconius and Eueides species from an overlapping area in Ecuador, comprising three mimicry groups, was investigated by GC/MS. The chemical signal serves as an anti-aphrodisiac signal that is transferred from males to females during mating, indicating the mating status of the female to prevent them from harassment by other males. In addition, the odour may also serve in predator defence. There is potential for convergence driven by mimicry, although, such convergence might be detrimental for species recognition of the butterflies within the mimicry ring, making mating more difficult. More than 500 compounds were detected, consisting of volatile, semi-volatile or non-volatile compounds, including terpenes, fatty acid esters or aromatic compounds. Several novel esters were identified by GC/MS and GC/IR data, microderivatisation and synthesis, including butyl (Z)-3-dodecenoate and other (Z)-3-alkenoates, 3-oxohexyl citronellate and 5-methylhexa-3,5-dienyl (E)-2,3-dihydrofarnesoate. The secretions were found to be species specific, potentially allowing for species differentiation. Statistical analysis of the compounds showed differentiation by phylogenetic clade and species, but not by mimicry group.

Characterisation and localisation of plant metabolites involved in pharmacophagy in the turnip sawfly

Several herbivorous insects consume certain metabolites from plants for other purposes than nutrition, such as defence. Adults of the turnip sawfly, Athalia rosae take up specific terpenoids, called clerodanoids, from Ajuga reptans. These metabolites are slightly modified by the sawflies and influence their mating behaviour and defence against predators. We characterised these metabolites and investigated their localisation in the insect and the specificity of the uptake and metabolite modification. Therefore, we performed feeding assays with adults and larvae of A. rosae as well as larvae of Spodoptera exigua, followed by chemical analyses. Two main clerodanoid-derived metabolites were detected in the abdomen and thorax but also on the surface of the adults. Small amounts were also found in larvae of the sawfly, while they were not detectable in S. exigua. Our findings provide new insights into the peculiarities of pharmacophagy and specialised metabolism in A. rosae.

Head and Tail Oxidized Terpenoid Esters from Androconia of Heliconius erato Butterflies

Heliconius erato is a neotropical butterfly species that is part of a complex mimicry ring, with colorful wing patterns. For intraspecific communication, males use pheromones that are released from two different scent-emitting structures. Scent glands located near the abdominal claspers of males, containing antiaphrodisiac pheromones, release a highly complex mixture of compounds that is transferred to females during mating, rendering them unattractive to other males. On the other hand, androconia, scent-emitting scale areas on the wings of male butterflies, release a structurally more restricted set of compounds that likely serves an aphrodisiac role. We report here on two structurally related compounds that are the major androconial constituents, produced in high amounts and are not volatile due to their high molecular mass. Their structures were established by extensive analysis of mass, infrared, and NMR spectra, as well as microderivatization reactions of the natural extract. After establishing synthetic access, the compounds were unequivocally identified as two unusual head and tail oxidized terpenoids, (4E,8E,12E)-4,8,12-trimethyl-16-oxoheptadeca-4,8,12-trien-1-yl oleate (1) and stearate (2). Although behavioral assays are necessary to fully comprehend their role in the chemical communication of the species, hypotheses for their use by the butterflies are also discussed.

Identification and Synthesis of a Macrolide as an Anti-aphrodisiac Pheromone from Males of Heliconius erato phyllis

Investigation of the contents of the scent glands of the heliconiine butterfly Heliconius erato phyllis via gas chromatography/electroantennography revealed an unprecedented active compound. The males transfer this compound to females during mating. The structure of (2R,6E,10R)-2,6-dimethyl-6-undecen-10-olide, a derivative of geranylacetone, was proposed on the basis of infrared and mass spectrometry spectra and microderivatization and confirmed by racemic and stereoselective syntheses. Bioassays with the synthetic macrolide showed the repellency of this compound, termed phyllisolide, when applied to scent glands of females, identifying it as an anti-aphrodisiac pheromone.

MACE - An Open Access Data Repository of Mass Spectra for Chemical Ecology

MACE is an open access collection of electron impact (EI) mass spectra for coupled gas chromatography-mass spectrometry (GC/MS) that serves as an add-on database, comprising curated spectra not present in widely available commercial mass spectral libraries, such as the NIST or WILEY databases. The spectra are stored as text files that allow easy integration into individual GC/MS systems. The article describes the concept of MACE, the data structure, how to contribute, and its usage. MACE is designed as a community effort and will require contributions from the community to be successful.

The scent chemistry of butterflies

Butterflies use structurally highly diverse volatile compounds for communication, in addition to visual signals. These compounds originate from plants or a formed de novo especially by male butterflies that possess specific scent organs.