3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly <i>Ithomia salapia</i>

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, <i>Ithomia salapia aquinia</i> and <i>I. s. derasa.</i> The major components were identified as isoprenyl (3-methyl-3-butenyl) (<i>Z</i>)-3-acetoxy-11-octadecenoate, isoprenyl (<i>Z</i>)-3-acetoxy-13-octadecenoate (<b>12</b>) and isoprenyl 3-acetoxyoctadecanoate (<b>11</b>) by GC/MS and GC/IR analyses, microderivatizations, and synthesis of representative compounds. The absolute configuration of <b>12</b> was determined to be <i>R</i>. 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>I. s. aquinia</i> contained ithomiolide A (<b>3</b>), a pyrrolizidine alkaloid derived γ-lactone, <i>I. s. derasa</i> carried the sesquiterpene α-elemol (<b>8</b>) 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.