Effects of surface topography and chemistry of Rumex obtusifolius leaves on the attachment of the beetle Gastrophysa viridula

Broad‐leaved dock, Rumex obtusifolius L. (Polygonaceae), is the main host plant of the green dock beetle, Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae). Adult beetles are able to attach and walk on leaves of this plant. Leaf surface is rather uneven, because of irregularly shaped prominent epidermal cells with a maximum height of about 9 µm. The surface is covered with a smooth epicuticular wax layer having relatively low free surface energy (FSE). The aim of this study was to measure beetle attachment force applying a ‘centrifugal technique’ on adult insects on the leaf surface and other substrates, in order to understand the effect of surface architecture and its physicochemical properties on insect attachment. We compared forces on an adaxial leaf surface with forces on a smooth silanized glass plate having low FSE, and on a polishing paper having slightly lower FSE and similar surface roughness (asperities’ size = 9 µm). Smooth plate made of normal untreated clean glass with high FSE was used as a reference substrate. On the leaf surface and the polishing paper, attachment forces were lower compared to both glass samples. There was no significant difference between force values on leaves and the polishing paper, but on both glass surfaces they were significantly higher than on the other substrates. Hydrophobicity alone explains a decrease in attachment force of the beetle, but when combined with roughness the decrease in force is four times greater.

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