Identification and biosynthesis of novel male specific esters in the wings of the tropical butterfly, Bicyclus martius sanaos

The Cuticular Hydrocarbons of Dasineura Oleae Show Differences Between Sex, Adult Age and Mating Status

In insects, cuticular lipids prevent water loss and act as semiochemicals. Because of their ecological function, the profile change across the insects' sex and development offers insight into insect biology and possible tools for pest management. Here, the first work on cecidomyiid cuticular extracts is proposed considering Dasineura oleae (Diptera: Cecidomyiidae) males and females at different adult ages (0-12 h, 12-24 h, 24-36 h) and distinct sexual conditions (virgin and mated). A set of 49 compounds were recorded (12 alkanes, 1 monomethyl alkane, 11 fatty acids, 4 esters, 1 aldehyde, 1 allylbenzene, 1 amine, 1 flavonoid, 1 ketone, 1 phenol, 1 steradiene, 1 sterol, 1 terpene, 1 triterpene and 11 unknown compounds), and 18 of them showed significant differences between groups. Among alkanes, hexacosane (nC26) exhibited a decreasing trend from the youngest to the oldest females, while pentacosane (nC25) and nonacosane (nC29) showed a decreasing trend from 0 to 12 h to 12-24 h virgin females. In addition, nonadecane (nC19) was significantly more abundant in the youngest males compared to older males and females. The alkanes nC25, nC26 and nC29 have been reported to be age-related also in other dipterans, while nC19 has been described as gender-specific chemical cue for platygastrid parasitoids. Further behavioural trials and analyses are required to assign the specific ecological roles to the characterized compounds. Our results may contribute to develop new low-impact control strategies relying on the manipulation of D. oleae's chemical communication (e.g. disruption of mating or species recognition). HIGHLIGHTS: • Cuticular hydrocarbons are often involved in dipteran intraspecific communication. • We explored the cuticular profile of D. oleae at different age, sex, mating condition. • Five alkanes and one mono-methyl alkane showed differences among groups. • Linoleic acid is the most abundant compound in virgins, absent in mated insects. • Eleven compounds disappear in mated insects, but were present in all virgins.

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.

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

The butterfly Heliconius erato occurs in various mimetic morphs. The male clasper scent gland releases an anti‐aphrodisiac pheromone and additionally contains a complex mixture of up to 350 components, varying between individuals. In 114 samples of five different mimicry groups and their hybrids 750 different compounds were detected by gas chromatography/mass spectrometry (GC/MS). Many unknown components occurred, which were identified using their mass spectra, gas chromatography/infrared spectroscopy (GC/IR)‐analyses, derivatization, and synthesis. Key compounds proved to be various esters of 3‐oxohexan‐1‐ol and (Z)‐3‐hexen‐1‐ol with (S)‐2,3‐dihydrofarnesoic acid, accompanied by a large variety of other esters with longer terpene acids, fatty acids, and various alcohols. In addition, linear terpenes with up to seven uniformly connected isoprene units occur, e. g. farnesylfarnesol. A large number of the compounds have not been reported before from nature. Discriminant analyses of principal components of the gland contents showed that the iridescent mimicry group differs strongly from the other, mostly also separated, mimicry groups. Comparison with data from other species indicated that Heliconius recruits different biosynthetic pathways in a species‐specific manner for semiochemical formation.

Fermentation Enhanced Biotransformation of Compounds in the Kernel of Chrysophyllum albidum

Chrysophyllum albidum Linn (African star apple) is a fruit with extensive nutritional and medicinal benefits. The fruit and kernel in the seed are both edible. Strains of lactic acid bacteria (LAB) were isolated from fermented seeds and assessed for probiotic characteristics. The extracts in both the unfermented and the fermented aqueous extracts from the kernels obtained from the seeds of C. albidum were subjected to analysis using the gas chromatography/mass spectrometry (GC-MS) method. This analysis identified the bioactive compounds present as possible substrate(s) for the associated organisms inducing the fermentation and the resultant biotransformed products formed. Three potential probiotic LAB strains identified as Lactococcus raffinolactis (ProbtA1), Lactococcus lactis (ProbtA2a), and Pediococcus pentosaceus (ProbtA2b) were isolated from the fermented C. albidum seeds. All strains were non hemolytic, which indicated their safety, Probt (A1, A2a, and A2b) grew in an acidic environment (pH 3.5) during the 48-h incubation time, and all three strains grew in 1% bile, and exhibited good hydrophobicity and auto-aggregation properties. Mucin binding proteins was not detected in any strain, and bile salt hydrolase was detected in all the strains. l-lactic acid (28.57%), norharman (5.07%), formyl 7E-hexadecenoate (1.73%), and indole (1.51%) were the four major constituents of the fermented kernel of the C. albidum, while 2,5-dimethylpyrazine (C1, 1.27%), 3,5-dihydroxy-6-methyl-2,3-dihydropyran-4-one (C2, 2.90%), indole (C3, 1.31%), norharman (C4, 3.01%), and methyl petroselinate (C5, 4.33%) were the five major constituents of the unfermented kernels. The isolated LAB are safe for consumption. The fermenting process metabolized C1, C2, and C5, which are possible starter cultures for the growth of probiotics. Fermentation is an essential tool for bioengineering molecules in foods into safe and health beneficial products.

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

Male ithomiine butterflies (Nymphalidae: Danainae) have hairpencils on the forewings (i.e., androconia) that disseminate semiochemicals during courtship. While most ithomiines are known to contain derivatives of pyrrolizidine alkaloids, dihydropyrrolizines, or γ-lactones in these androconia, here we report on a new class of fatty acid esters identified in two subspecies, Ithomia salapia aquinia and I. s. derasa. The major components were identified as isoprenyl (3-methyl-3-butenyl) (Z)-3-acetoxy-11-octadecenoate, isoprenyl (Z)-3-acetoxy-13-octadecenoate (12) and isoprenyl 3-acetoxyoctadecanoate (11) by GC/MS and GC/IR analyses, microderivatizations, and synthesis of representative compounds. The absolute configuration of 12 was determined to be R. The two subspecies differed not only in the composition of the ester bouquet, but also in the composition of more volatile androconial constituents. While some individuals of I. s. aquinia contained ithomiolide A (3), a pyrrolizidine alkaloid derived γ-lactone, I. s. derasa carried the sesquiterpene α-elemol (8) in the androconia. These differences might be important for the reproductive isolation of the two subspecies, in line with previously reported low gene exchange between the two species in regions where they co-occur. Furthermore, the occurrence of positional isomers of unsaturated fatty acid derivatives indicates activity of two different desaturases within these butterflies, Δ9 and Δ11, which has not been reported before in male Lepidoptera.

Cuticular Chemistry of the Queensland Fruit Fly Bactrocera tryoni (Froggatt)

The cuticular layer of the insect exoskeleton contains diverse compounds that serve important biological functions, including the maintenance of homeostasis by protecting against water loss, protection from injury, pathogens and insecticides, and communication. Bactrocera tryoni (Froggatt) is the most destructive pest of fruit production in Australia, yet there are no published accounts of this species' cuticular chemistry. We here provide a comprehensive description of B. tryoni cuticular chemistry. We used gas chromatography-mass spectrometry to identify and characterize compounds in hexane extracts of B. tryoni adults reared from larvae in naturally infested fruits. The compounds found included spiroacetals, aliphatic amides, saturated/unsaturated and methyl branched C12 to C20 chain esters and C29 to C33 normal and methyl-branched alkanes. The spiroacetals and esters were found to be specific to mature females, while the amides were found in both sexes. Normal and methyl-branched alkanes were qualitatively the same in all age and sex groups but some of the alkanes differed in amounts (as estimated from internal standard-normalized peak areas) between mature males and females, as well as between mature and immature flies. This study provides essential foundations for studies investigating the functions of cuticular chemistry in this economically important species.

Structures related to pheromone storage in alar androconia and the female abdominal scent gland of Heliconius erato phyllis, Heliconius ethilla narcaea, and Heliconius besckei (Lepidoptera: Nymphalidae: Heliconiinae)

We describe the morphology of alar androconia and the female abdominal scent gland of Heliconius erato phyllis, Heliconius ethilla narcaea, and Heliconius besckei. Androconial scales of Heliconius, which are arranged in overlapping wing bands, release pheromones during courtship, probably through vibratory movements of male wings over the female to induce her to mate. An antiaphrodisiac is produced by glands located in the valves of the male and is transferred during copulation to the yellow dorsal abdominal sac present in the virgin female, causing this sac to emit a scent that reduces the attractiveness of the female for courtship with other males. Stereomicroscopy, SEM, and TEM analyses were conducted to describe the morphology of the internal and external scales and the external abdominal scent sac. The findings revealed different sizes of external androconial scales and an internal group of porous structural vesicles that are probably related to the preservation of internal space, reception and storage of secretions, and elimination of volatiles when the male is actively involved in courtship. Translucent projections on the female abdominal scent sac create open reservoirs for the reception, storage, and emission of antiaphrodisiac volatiles along with stink clubs. Male valve denticles vary in form and probably attach securely to the female sac during mating, thus ensuring secretion transfer. These features are discussed in the context of a comparative analysis.

Insecticidal Activity of Methyl Benzoate Analogs Against Red Imported Fire Ants, Solenopsis invicta (Hymenoptera: Formicidae)

Although insecticidal properties of certain benzoates have been investigated for pest insects and mites, toxicity of benzoates to the red imported fire ants, Solenopsis invicta Buren, has never been reported. In this study, 15 commercially available benzoates were assessed for their contact and fumigation toxicity to S. invicta workers and their chemical structure-activity relationships. Among tested benzoates, benzylbenzoate, n-pentybenzoate, and n-hexylbenzoate were three most potent contact toxins against S. invicta workers (mean LD50 value = 23.31, 35.26, 35.99 µg per ant, respectively) and methyl-3-methoxybenzoate, methyl-3-methylbenzoate, and methylbenzoate were the three most potent fumigants (mean LC50 value = 0.61, 0.62, 0.75 µg/ml, respectively). For nonsubstituted alkyl benzoates (esters of benzoic acid and C1-C6 linear alcohols), the contact toxicity was positively correlated to the alkyl chain length (r = 0.89), while the fumigation toxicity was negatively correlated (r = 0.90). Presence of a methoxyl group at either the ortho or meta position of methylbenzoate significantly increased its contact toxicity, so did a methyl group at meta position. However, presence of a methyl group at ortho position reduced the contact toxicity. Presence of methyl or methoxyl group at the meta position did not have significant effect on the fumigation toxicity; however, methyl, methoxyl, chloro, or nitro groups at the ortho position significantly reduced fumigation toxicity. Hexylbenzoate has neither known Occupational Safety and Health Administration hazards nor aquatic toxicity, and methyl 3-methoxybenzoate is not considered a hazardous substance, indicating a great potential for their application in fire ant management.

The Scent Chemistry of Heliconius Wing Androconia

Neotropical Heliconius butterflies are members of various mimicry rings characterized by diverse colour patterns. In the present study we investigated whether a similar diversity is observed in the chemistry of volatile compounds present in male wing androconia. Recent research has shown that these androconia are used during courting of females. Three to five wild-caught male Heliconius individuals of 17 species and subspecies were analyzed by GC/MS. Most of the identified compounds originate from common fatty acids precursors, including aldehydes, alcohols, acetates or esters preferentially with a C₁₈ and C₂₀ chain, together with some alkanes. The compounds occurred in species-specific mixtures or signatures. For example, octadecanal is characteristic for H. melpomene, but variation in composition between the individuals was observed. Cluster analysis of compound occurrence in individual bouquets and analyses based on biosynthetic motifs such as functional group, chain length, or basic carbon-backbone modification were used to reveal structural patterns. Mimetic pairs contain different scent bouquets, but also some compounds in common, whereas sympatric species, both mimetic and non-mimetic, have more distinct compound compositions. The compounds identified here may play a role in mate choice thus helping maintain species integrity in a butterfly genus characterized by pervasive interspecific gene flow.

Differentiation in putative male sex pheromone components across and within populations of the African butterfly Bicyclus anynana as a potential driver of reproductive isolation

Sexual traits are often the most divergent characters among closely related species, suggesting an important role of sexual traits in speciation. However, to prove this, we need to show that sexual trait differences accumulate before or during the speciation process, rather than being a consequence of it. Here, we contrast patterns of divergence among putative male sex pheromone (pMSP) composition and the genetic structure inferred from variation in the mitochondrial cytochrome oxidase 1 and nuclear CAD loci in the African butterfly Bicyclus anynana (Butler, 1879) to determine whether the evolution of "pheromonal dialects" occurs before or after the differentiation process. We observed differences in abundance of some shared pMSP components as well as differences in the composition of the pMSP among B. anynana populations. In addition, B. anynana individuals from Kenya displayed differences in the pMSP composition within a single population that appeared not associated with genetic differences. These differences in pMSP composition both between and within B. anynana populations were as large as those found between different Bicyclus species. Our results suggest that "pheromonal dialects" evolved within and among populations of B. anynana and may therefore act as precursors of an ongoing speciation process.

Selection on male sex pheromone composition contributes to butterfly reproductive isolation

Selection can facilitate diversification by inducing character displacement in mate choice traits that reduce the probability of maladaptive mating between lineages. Although reproductive character displacement (RCD) has been demonstrated in two-taxa case studies, the frequency of this process in nature is still debated. Moreover, studies have focused primarily on visual and acoustic traits, despite the fact that chemical communication is probably the most common means of species recognition. Here, we showed in a large, mostly sympatric, butterfly genus, a strong pattern of recurrent RCD for predicted male sex pheromone composition, but not for visual mate choice traits. Our results suggest that RCD is not anecdotal, and that selection for divergence in male sex pheromone composition contributed to reproductive isolation within the Bicyclus genus. We propose that selection may target olfactory mate choice traits as a more common sensory modality to ensure reproductive isolation among diverging lineages than previously envisaged.