Sexual dimorphism in the lipid fraction of the defensive secretion ofGastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract

Abstract. The lipid fraction of the defensive secretion of adult Gastrophysa viridula was analyzed by gas-liquid chromatography and gas chromatography-mass spectrometry. Three long chain acetates and two methyl-branched hydrocarbons were identified and their amounts in the secretion of single field-collected and laboratory-reared beetles determined. The composition of the secretion was affected by the sex, reproductive status, and age of the beetle. The ratio of (Z)-I 1-eicosenyl acetate to (Z)-I 3-docosenyl acetate ranged from 0.30 to 0.78 in male beetles and from 1.05 to 2.06 in female beetles. The biological significance of this sexual dimorphism is discussed.Key words. Gastrophysa viridula; Chrysomelidae; Coleoptera; chemical defence; acetates; hydrocarbons; gas-liquid chromatography; gas chromatography-mass spectrometry; sexual dimorphism.The remarkable diversity of defensive chemicals of leaf beetles (Chrysomelidae) has received considerable attention from both chemists and biologists (refs in 1, 2). As is typical of arthropod chemical defence 3~4, the defensive secretions of adult chrysometids are characterized by an amazingly complex mixture of major and minor components, the biological significance of which, however, is poorly understood. Whereas the predominant components of a secretion may be most important for its chemical properties, the minor components could exert ~ubtle biological effects or could act synergistically 5. To assess the biological functions of a defensive secretion it is thus necessary to investigate both its major and minor components. So far, however, only the major components of chrysomelid defensive secretions have been studied extensively; much less is known about the minor components. The predominant components of the defensive secretion of adult Gastrophysa viridula are de novo synthesized isoxazolinone glycosides bearing nitropropanoic acid moieties. Nitropropanoic acid itself is known to be toxic and a feeding deterrent for a wide variety of organisms (refs in 2). In addition to these compounds, Pasteels et al. 6 reported the presence of unidentified saturated hydrocarbons in the secretion. In order to get an insight into the biological function of the exocrine secretion of G. viridula, its as yet unidentified lipid components were investigated. The results are reported here. Materials and methods Insects. Adult Gastrophysa viridula were collected closeto the campus of the University of Brussels. In the laboratory they were maintained individually in separate plastic containers on their food plant Rumex obtusifolius. The offspring of 12 randomly selected females were raised in a light-dark regime of 16 h/8 h and a temperature of 20 ~ and 15 ~ respectively. Development was completed after 20 days. A total of 144 offspring (12 per family) were divided into two groups. The beetles of the first group were maintained individually, those of the second group in pairs. Two randomly selected paired and unpaired beetles of each family were 'milked' at the age of 9 days and 16 days, ...

Comparison of tarsal and cuticular chemistry in the leaf beetle Gastrophysa viridula (Coleoptera: Chrysomelidae) and an evaluation of solid-phase microextraction and solvent extraction techniques

“…Some substances with high abundances in G. viridula cuticular lipids (i-methylheptacosane and i-methylnonacosane) have been shown to be contact sex pheromones in the Japanese green dock leaf beetle, G. atrocyanaea (Sugeno et al 2006) and might act in a similar way in G. viridula. Furthermore, 11-eicosenyl acetate, which we found in most samples in this study, is a defensive component in both, G. viridula and G. atrocyanaea (Eggenberger et al 1994;Sugawara et al 1978) and its presence in the SPME samples of elytra and in surface extracts is easily explained by the fact that, in leaf beetles, the openings of the defensive glands are located on the elytra and pronotum (Deroe and Pasteels 1982).…”

“…All extracts were checked for purity by means of gas chromatography (see below). The sex of the beetles was not taken into account, because apparent sex-specific differences in the lipid composition were only found in beetles that were older than our test batch (Eggenberger et al 1994; own observations).…”

Sex and habitat differences in size and coloration of an amphibian's poison glands match differential predator pressures

“…1991; Eggenberger et al . 1994) sex differences in toxin productions have been detected, which may be a consequence of one sex being more dependent on chemical defenses than the other.…”

Sequestration of plant compounds in a leaf beetle's defensive secretion: cardenolides in Chrysochus

“…The biologically most interesting question about the exocrine secretions of Chrysochus described here, is whether these secretions are actually produced to defend the insects against predators [and not for instance for some kind of intra-or interspecific communication (e.g., Eggenberger et al 1994;Hilker 1989)]. The timing of their release -i.e., as soon as the insect is disturbed -strongly suggests such a function as does the resemblance to those of other leaf beetles where their defensive character could be demonstrated (Pasteels et al 1988Rowell-Rahier et al 1995).…”