The pheromone system of the male danaine butterfly, Idea leuconoe

Complete mitochondrial genome of Idea leuconoe (Lepidoptera: Danaidae) and related phylogenetic analyses

In the present study, we first sequenced and determined the complete mitochondrial genome (mitogenome) of the giant Danaidae butterfly, Idea leuconoe (Lepidoptera: Danaidae). The mitogenome was a typical closed, circular, double-stranded DNA molecule of 15,278 bp length (GenBank accession number: KR815449), similar to the metazoan mitogenomes containing 37 genes and one A + T-rich region. All the protein-coding genes (PCGs) were initiated with a typical ATN codon. Seven genes (COII, ATP6, COIII, nad4, nad4L, cytb, and nad1) adopted the standard ATG start codon, but the remaining six genes were initiated with ATA. All the 13 PCGs harbored complete termination codons (TAA). The overlap nucleotides ATGATAA were conserved for the ATP8/ATP6 gene. The largest intergenic spacer was located between trnGln and nad2, a common finding in Lepidoptera butterflies. All the transfer RNA genes in the I. leuconoe mitogenome could be folded into typical clover-leaf secondary structures, except for trnSer (AGN) that lacked a dihydrouridine arm. The control region with 94.8% A + T content was 444 bp in length and located between rrnS and trnMet. Finally, the phylogenetic relationships obtained using the maximum likelihood and Bayesian methods confirmed two well-supported phylogenetic trees of Danaidae, Papilionidae, and Nymphalidae from the order Lepidoptera, which were consistent with the traditional morphological classification. Results provided additional information for butterfly phylogenetic analysis and insights into the evolution of genomes.

Sex pheromones from male forewings of the Common Grass Yellow Eurema mandarina

The common grass yellow Eurema mandarina has a characteristic patch (sex brand) composed of specialized scales (androconia) and wing intermembranous cells on the ventral surface of its male forewing. This structure is specific to males and is thought to release compounds that induce female mate acceptance. However, no study has demonstrated that these compounds function as sex pheromones in the genus Eurema. Here we report the identification of sex pheromones in males of E. mandarina. Chemical analyses revealed that 6,10,14-trimethylpentadecan-2-one (TMP) and (E/Z)-3,7,11,15-tetramethylhexadec-2-enal [(E/Z)-phytal] were male-specific and abundant in particular regions of the male forewings. TMP was highest in the sex brand, whereas (E/Z)-phytal was concentrated in the anal cell (cell 2 A), lacking androconia and intermembranous cells. The content of these compounds increases with age in males after emergence. In bioassays, virgin females displayed a posture of bending their abdomens as mating acceptance in response to stimulation by fresh male forewings. However, solvent-washed male wings did not induce such female responses, suggesting that some compounds from male wings serve as triggers. When we examined female responses to compounds applied to solvent-washed male wings, authentic TMP and (E/Z)-phytal alone showed little activity. However, the mixture elicited abdomen-bending responses in one-third of the females. Therefore, TMP and (E/Z)-phytal were found to act synergistically as aphrodisiac sex pheromones for E. mandarina females, although these activities were weak.

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.

A major locus controls a biologically active pheromone component in Heliconius melpomene

Understanding the production, response, and genetics of signals used in mate choice can inform our understanding of the evolution of both intraspecific mate choice and reproductive isolation. Sex pheromones are important for courtship and mate choice in many insects, but we know relatively little of their role in butterflies. The butterfly Heliconius melpomene uses a complex blend of wing androconial compounds during courtship. Electroantennography in H. melpomene and its close relative Heliconius cydno showed that responses to androconial extracts were not species specific. Females of both species responded equally strongly to extracts of both species, suggesting conservation of peripheral nervous system elements across the two species. Individual blend components provoked little to no response, with the exception of octadecanal, a major component of the H. melpomene blend. Supplementing octadecanal on the wings of octadecanal-rich H. melpomene males led to an increase in the time until mating, demonstrating the bioactivity of octadecanal in Heliconius. Using quantitative trait locus (QTL) mapping, we identified a single locus on chromosome 20 responsible for 41% of the parental species' difference in octadecanal production. This QTL does not overlap with any of the major wing color or mate choice loci, nor does it overlap with known regions of elevated or reduced FST . A set of 16 candidate fatty acid biosynthesis genes lies underneath the QTL. Pheromones in Heliconius carry information relevant for mate choice and are under simple genetic control, suggesting they could be important during speciation.

In vivo real-time monitoring of aphrodisiac pheromone release of small white cabbage butterflies (Pieris rapae)

The study of insect behavior is of practical importance for developing possible control methods in Integrated Pest Management. Currently, one model of butterfly mating behavior suggests that the initial location of potential mates occurs visually followed by the release of one or more short-range male aphrodisiac pheromones. This model is supported by data obtained from field observations and inferences based on the behavioral effects of chemicals extracted or isolated using indirect and offline techniques. In this study, we performed in vivo real-time monitoring of the male aphrodisiac pheromones released by the small white cabbage male butterfly (Pieris rapae Linnaeus) using confined direct analysis in real time (cDART) mass spectrometry. cDART is a new method easily adapted to the study in real time of chemicals released into the environment by virtually any insect. The major compound released by the male Pieris rapae was identified as ferrulactone. The experimental results reported here indicate that the release of ferrulactone occurs less than 1s after the male visualizes its partner, and reaches a maximum after about one half minute. This study is the first reported in vivo detection and monitoring of butterfly male aphrodisiac pheromones in real time.

The use of the lactone motif in chemical communication

A wide variety of organisms communicate via the chemical channel using small molecules. A structural feature quite often found is the lactone motif. In the present paper, the current knowledge on such lactones will be described, concentrating on the structure, chemistry, function, biosynthesis and synthesis of these compounds. Lactone semiochemicals from insects, vertebrates and bacteria, which this article will focus on, are particularly well investigated. In addition, some ideas on the advantageous use of lactones as volatile signals, which promoted their evolutionary development, will be discussed.

Chemical ecology of insect-plant interactions: ecological significance of plant secondary metabolites

Plants produce a diverse array of secondary metabolites as chemical barriers against herbivores. Many phytophagous insects are highly adapted to these allelochemicals and use such unique substances as the specific host-finding cues, defensive substances of their own, and even as sex pheromones or their precursors by selectively sensing, incorporating, and/or processing these phytochemicals. Insects also serve as pollinators often effectively guided by specific floral fragrances. This review demonstrates the ecological significance of such plant secondary metabolites in the highly diverse interactions between insects and plants.

Supinidine Viridiflorates from the Roots of Chromolaena pulchella

The alkaloid extract from the roots of Chromolaena pulchella provided two new pyrrolizidine alkaloids, elucidated as (-)-supinidine triviridiflorate (1) and (-)-supinidine diviridiflorate (2) based on their physical and spectroscopic properties. Their absolute configuration was determined by chemical correlation with (-)-supinidine (3) and (+)-viridifloric acid (4).

The scent of bacteria: headspace analysis for the discovery of natural products

Volatile compounds released by 50 bacterial strains, 45 of them actinobacteria in addition to three chloroflexi and two myxobacteria, have been collected by use of a closed-loop stripping apparatus, and the obtained headspace extracts have been analyzed by GC-MS. Excluding terpenes that have recently been published elsewhere, 254 compounds from all kinds of compound classes have been identified. For unambiguous compound identification several reference compounds have been synthesized. Among the detected volatiles 12 new natural products have been found, in addition to mellein, which was released by Saccharopolyspora erythraea. The iterative PKS for this compound has recently been identified by in vitro experiments, but mellein production in S. erythraea has never been reported before. These examples demonstrate that headspace analysis is an important tool for the discovery of natural products that may be overlooked using conventional techniques. The method is also useful for feeding experiments with isotopically labeled precursors and was applied to investigate the biosynthesis of the unusual nitrogen compound 1-nitro-2-methylpropane, which arises from valine. Furthermore, several streptomycetes emitted compounds that were previously recognized as insect pheromones, thus questioning if bacterial symbionts are involved in insect communication.

The biosynthesis of hexahydrofarnesylacetone in the butterfly Pieris brassicae

Hexahydrofarnesylacetone (6,10,14-trimethylpentadecan-2-one, 1) is a widespread ketone occurring in plants and insects. Several species use this compound or the respective alcohol as part of their pheromone bouquet. Here, we showed by using deuterium labeled phytol (3) and GC-MS experiments that the Large Cabbage White butterfly Pieris brassicae can take up phytol in the larval stage and transforms it into 1 by oxidative degradation.

Aphrodisiac pheromones from the wings of the small cabbage white and large cabbage white butterflies, Pieris rapae and Pieris brassicae

The small and large cabbage butterflies, Pieris rapae and P. brassicae, are found worldwide and are of considerable economic importance. The composition of the male scent-producing organs present on the wings was investigated. More than 120 components were identified, but only a small portion proved to be male specific. Major components were the known beetle pheromone ferrulactone (1) in P. rapae and its previously unknown larger analogue, brassicalactone (2), in P. brassicae. The latter carries an additional isoprene unit and is closely related to 1. Other components present in larger amounts on male relative to female wings were hexahydrofarnesylacetone (18) and phytol (23). Brassicalactone (2) was fully characterized by synthesis of its various diastereomers by using ring-closing metathesis. A similar approach to ferrulactone (1) failed, presumably because of its smaller ring size. Instead, this compound was synthesized by using a modified literature procedure. The biological activity of the compounds in the extract was tested by coupled gas chromatographic-electroantennographic (GC-EAD) analysis, which showed that both macrolides and the other major components of the wings can be detected by the antennae of the conspecific female butterflies. Other detectable compounds included several alkanes, which are typical constituents of the butterfly cuticula, derivatives of phytol (23) and long-chain secondary alcohols. Finally, bioassays with males showed that the mixture of 1 (P. rapae) or 2 (P. brassicae) together with 18 and 23 applied to freshly eclosed males increased mating success compared to untreated males. Therefore, the two macrolides 1 and 2 are aphrodisiac pheromone components of male small and large cabbage white butterflies, respectively.

Major components in the hairpencil secretion of a butterfly, Euploea mulciber (Lepidoptera, Danaidae): their origins and male behavioral responses to pyrrolizidine alkaloids

Two compounds, 9,10-epoxytetrahydroedulan (ET) and viridiflorine beta-lactone (VL), were identified as major components from the hairpencils of field-caught males of a danaid butterfly, Euploea mulciber. By contrast, laboratory-reared males entirely lacked VL, but possessed a significant quantity of ET. Various feeding experiments with larvae and indoor adult males strongly suggested that ET is biosynthesized de novo only after eclosion from nutrients ingested during the larval development. Since VL was suspected to be derived from pyrrolizidine alkaloids (PAs) acquired as an adult, tests for feeding response to and oral administration of four PAs (a 4:1 mixture of intermedine/lycopsamine, heliotrine, monocrotaline, and retronecine) were conducted. When the tarsi or proboscis were stimulated with PA solutions, males showed positive feeding responses (proboscis extension and sucking movements) to intermedine/lycopsamine, heliotrine, and retronecine in decreasing order of responsiveness, thereby providing evidence that male adults are endowed with taste receptor(s) specific to PAs on the legs as well as on the proboscis. Differently from gustatory responsiveness, only males fed with intermedine/lycopsamine produced a significant quantity of VL (ca. 35 microg/male), whereas those that ingested heliotrine or monocrotaline hydrochloride produced traces of VL (<0.18 microg/male). Uptake of retronecine did not lead to VL formation at all. In behavioral bioassays to test the attractivity of PAs to males, all individuals tested were attracted exclusively to intermedine/lycopsamine. This shows that certain PA(s) per se serve as attractant(s) for males in locating PA sources, and further suggests that in the field, males will seek particular PA(s) that are indispensable as precursors for the efficient biosynthesis of VL.

Volatile Organic Compounds from Arctic Bacteria of theCytophaga-Flavobacterium-Bacteroides Group: A Retrobiosynthetic Approach in Chemotaxonomic Investigations

Volatile organic compounds emitted by different marine arctic strains of the Cytophaga-Flavobacterium-Bacteroides group were investigated by using a modified closed-loop stripping apparatus (CLSA). Seven of nine strains emitted volatiles, dominated by methyl ketones, in specific patterns. The methyl ketones were aliphatic saturated, or unsaturated, and comprised 12 to 18 C-atoms, sometimes with terminal Me branches. They were identified by GC/MS, retention-index calculations, derivatization with dimethyl disulfide for C=C bond location, and GC/FTIR to elucidate their uniform (Z)-configuration. The proposed structures of all methyl ketones were subsequently confirmed by synthesis, while the absolute configuration of chiral volatiles was elucidated by stereoselective synthesis. From retrobiosynthetic considerations, it was found that strain ARK10267 uses mainly valine, and strain ARK10063 mainly isoleucine for formation of starters for the ketone biosynthesis, which is correlated to fatty acid biosynthesis. Four strains (ARK10223, ARK10044, ARK10141, and ARK10146) use leucine. These separations are supported by phylogenetic affiliations based on 16S rRNA. Strain ARK10255b, in the course of this study found to be not a member of the Cytophaga-Flavobacterium-Bacteroides phylum, did not emit aliphatic ketones of medium chain length, but methionine-derived 4-(methylsulfanyl)butan-2-one and corresponding 4-(methylsulfanyl)butan-2-ol. Most of the compounds described have not been reported previously from nature.