Friction force reduction triggers feet grooming behaviour in beetles

Abstract

In insects, cleaning (grooming) of tarsal attachment devices is essential for maintaining their adhesive ability, necessary for walking on a complex terrain of plant surfaces. How insects obtain information on the degree of contamination of their feet has remained, until recently, unclear. We carried out friction force measurements on walking beetles Gastrophysa viridula (Coleoptera, Chrysomelidae) and counted grooming occurrence on stiff polymer substrata with different degrees of nanoroughness (root mean square: 28 -288 nm). Since nanoscopically, rough surfaces strongly reduced friction and adhesion without contaminating feet, we were able to demonstrate, for the first time to our knowledge, that friction force between tarsal attachment pads and the substrate provides an insect with information on the degree of contamination of its attachment structures. We have shown that foot grooming occurrence correlates not only with the degree of contamination but also with the decrease of friction force. This result indicates that insects obtain information about the degree of contamination, not statically but rather dynamically and, presumably, use mechanoreceptors monitoring either tensile/compressive forces in the cuticle or tensile forces between leg segments.

Surface roughness effects on attachment ability of the spider Philodromus dispar (Araneae, Philodromidae)

“…Similar effects have previously been demonstrated in other hairy attachment devices of flies (Peressadko and Gorb, 2004b), beetles (Peressadko and Gorb, 2004b;Voigt et al, 2008;Hosoda and Gorb, 2011;Bullock and Federle, 2011) and geckos (Huber et al, 2007). All these studies have revealed the presence of a so-called critical roughness, where contact forces were strongly reduced.…”

“…However, the mechanism of adhesion reduction is not only based on the roughness itself but also may include some contamination effects Hosoda and Gorb, 2011) and adsorption of adhesive fluids Bauer and Federle, 2009;Gorb et al, 2010).…”

Evidence for a material gradient in the adhesive tarsal setae of the ladybird beetle Coccinella septempunctata

“…Under natural conditions, resilin is very likely always hydrated 28 . Beetles are known to produce tarsal liquids, which have been assumed to contribute to the adhesion capabilities by means of capillary processes 38,39 and cleaning effects 40,41 . Based on our assumption that the presence of high resilin concentrations in the setal tips increases the attachment ability of the adhesive pads, it becomes obvious that the hydration of resilin may be essential for keeping the attachment performance of the beetles on a high level.…”

Leaf beetle attachment on wrinkles: isotropic friction on anisotropic surfaces

“…The structure and performance of tarsal attachment devices in both beetle species have previously been well studied (e.g. Peressadko and Gorb, 2004;Schuppert et al, 2005;Voigt et al, 2008;Voigt et al, 2010;Gorb and Gorb, 2009;Bullock and Federle, 2009;Bullock and Federle, 2011;Clemente et al, 2010;Hosoda and Gorb, 2011;Prüm et al, 2012). Both species bear spatula-shaped lanceolate and filament-shaped tarsal adhesive setae in males and females, and additionally setae with discoid terminal tips only in males (Stork, 1980a;Pelletier and Smilowitz, 1987).…”