Abstract
Representatives of the highly speciose tropical butterfly genus Bicyclus (Lepidoptera: Nymphalidae) are characterized by morphological differences in the male androconia, a set of scales and hair pencils located on the surface of the wings. These androconia are assumed to be associated with the release of courtship pheromones. In the present study, we report the identification and biosynthetic pathways of several novel esters from the wings of male B. martius sanaos. We found that the volatile compounds in this male butterfly were similar to female-produced moth sex pheromones. Components associated with the male wing androconial areas were identified as ethyl, isobutyl and 2-phenylethyl hexadecanoates and (11Z)-11-hexadecenoates, among which the latter are novel natural products. By topical application of deuterium-labelled fatty acid and amino acid precursors, we found these pheromone candidates to be produced in patches located on the forewings of the males. Deuterium labels from hexadecanoic acid were incorporated into (11Z)-11-hexadecenoic acid, providing experimental evidence of a Δ11-desaturase being active in butterflies. This unusual desaturase was found previously to be involved in the biosynthesis of female-produced sex pheromones of moths. In the male butterflies, both hexadecanoic acid and (11Z)-11-hexadecenoic acid were then enzymatically esterified to form the ethyl, isobutyl and 2-phenylethyl esters, incorporating ethanol, isobutanol, and 2-phenylethanol, derived from the corresponding amino acids L-alanine, L-valine, and L-phenylalanine.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-014-0452-y) contains supplementary material, which is available to authorized users.
Highlights
In the insect order Lepidoptera, moths and butterflies differ in their use of pheromones for mate finding and mate recognition
We report the identification of several novel ethyl, isobutyl, and 2-phenylethyl esters in B. martius sanaos
We investigated the origin of the alcohols and the biosynthesis of the unsaturated fatty acyl moiety involving a Δ11-desaturase, an enzyme family that has previously been found typically in relation with moth sex pheromone biosynthesis
Summary
In the insect order Lepidoptera, moths and butterflies differ in their use of pheromones for mate finding and mate recognition. Mate finding in moths is mediated by female-emitted sex pheromones that elicit a fine-tuned response in conspecific males (Wyatt 2003). Pheromone biosynthesis in most moths involves a series of more or less well-described enzymatic reactions, including de novo synthesis of fatty acyl precursors, desaturation, and chain elongation or shortening to produce various carbon backbones, followed by transesterification to form corresponding fatty acid esters. There is no evidence for sex pheromones to be involved in long-range communication in butterflies: they appear to have lost this information channel used by female moths. Male-produced pheromones are commonly involved in close-range courtship displays (Vane-Wright and Boppré 1993). Detailed studies on the semiochemicals of butterflies include Nymphalids e.g. some Milkweed butterflies from the subfamily Danainae (Nishida et al 1996; Schulz et al 1993, 2004; Stritzke et al 2003) and some Heliconius spp. from the subfamily Heliconiinae (Schulz et al 2007, 2008), and Pierid butterflies such as Colias eurytheme and C. philodice from the subfamily Coliadinae (Grula et al 1980; Rutowski 1980), and Pieris
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