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

Abstract

Tarsal substrate adhesion in insects is based on the effect of a thin film of liquid in the contact zone, which is deposited as droplets on the surface an insect has walked on, but as yet, little is known about the chemical composition of the liquid. In the present study, interference reflection microscopical images of the tarsal contact and footprints of Gastrophysa viridula (Coleoptera: Chrysomelidae) are depicted and the chemical composition of tarsal liquids and cuticular components are investigated by means of solid-phase microextraction and solvent extraction of whole beetles and footprints. Based on this comparative methodical approach, we are first to provide evidence from direct sampling for the chemical congruence of cuticular lipids and tarsal liquid in beetles. Furthermore, differences resulting from the applied sampling techniques are assessed and advantages of the respective methods are discussed.

Congruence of epicuticular hydrocarbons and tarsal secretions as a principle in beetles

“…Recently, this has been confirmed for the leaf beetles L. decemlineata and G. viridula (Chrysomelidae) by means of direct sampling using the method applied in the present study (SF Geiselhardt et al 2009. All those investigations, however, have dealt with individual species.…”

“…Page et al 2002;Steiger et al 2007), methyl-branched olefins (e.g. Blomquist 2010;SF Geiselhardt et al 2009) and in a few cases non-hydrocarbon components, such as esters, aldehydes, ketones or alcohols (Buckner 2010; for details on the composition see Online Resource 1). n-alkanes (35 species), monomethylalkanes (34 species), and dimethylalkanes (33 species) were nearly omnipresent in our survey, followed by alkenes (27 species) and trimethylalkanes (20 species).…”

Influence of ambient humidity on the attachment ability of ladybird beetles (Coccinella septempunctata)

“…The tarsal secretions in hairy attachment pads of beetles were found to be mainly lipid-based [22,26–27 49–50], with only a small volatile fraction (likely water) [30]. Peisker et al [46] speculated that these secretions may have an additional function, apart from forming capillary bridges, which is to cover setal tips and thereby preventing the desiccation of setal tips, thus, keeping them in a soft rubber-like state.…”

Elasto-capillarity in insect fibrillar adhesion

“…The adhesive liquid mostly contains lipids [33], and the resulting low contact angle contributes to the robustness of the adhesion mechanism on a broad range of substrates. For the sake of simplicity, we here assume that the liquid perfectly wets both surfaces (zero contact angle).…”