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

Abstract

Dedicated to the memory of Wittko Francke.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 speciesspecific manner for semiochemical formation.

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

“…27 Recently, a comprehensive analysis of Heliconius clasper scent glands detecting 750 compounds in 114 individuals of 10 subspecies was published. 13 The compound designated "unknown B95 (1)" in this article is actually compound A. It occurs in 19 of the 114 individuals analyzed, always in small amounts, belonging to the subspecies Heliconius erato venustus, phyllis, amphitrite, microclea, and demophoon.…”

“…Considering the molecular formula, C 13 H 22 O 2 , a likely biosynthetic precursor of macrolide A would be (E)-geranylacetone, a common natural product in insects and known from H. erato. 13 As a result, a novel aliphatic 11-membered macrocyclic lactone structure, (E)-2,6-dimethyl-6-undecen-10-olide (8), was proposed as the structure of A. The postulated mass spectrometric fragmentations for compounds A and B are presented in Figure S1.…”

“…5,24 A recent thorough analysis of the contents of H. erato subspecies clasper scent glands revealed the presence of various macrolactones, usually with higher molecular weights. 13 However, the role of these macrolactones in the ecology of Heliconius is not clear.…”

“…It occurs in 19 of the 114 individuals analyzed, always in small amounts, belonging to the subspecies Heliconius erato venustus, phyllis, amphitrite, microclea, and demophoon. 13 Obviously, pyllisolide is usually present only as a minor component in clasper scent gland secretion but can still influence butterfly behavior. Although the high activity of trace components is well-known in other insects, including night-flying moths, it has not been observed thus far for compounds from butterfly scent glands that usually contain relatively large amounts of material.…”

“…These ions place the double bond at C-6. − Once this structural motif had been rationalized, a terpenoid compound seemed to be likely. Considering the molecular formula, C 13 H 22 O 2 , a likely biosynthetic precursor of macrolide A would be ( E )-geranylacetone, a common natural product in insects and known from H. erato …”