The influence of the topography and physico-chemical properties of the cuticle surface on the wettability and adhesive properties of the elytra of the dung beetleGeotrupes stercorarius(Coleoptera, Scarabaeidae)

Abstract

The elytral surface of dung beetles is generally accepted to be self-cleaning due to its anti-adhesive properties. In this article, the wettability and adhesive properties of elytral surface (intact and treated with Acetone and Ethanol) of the beetle Geotrupes stercorarius were characterized. Since these properties are influenced by the surface structure and chemistry, the micro- and nanostructure of the elytra were observed using scanning electron microscopy and the surface roughness were estimated with white light interferometery, whereas the water contact angle and adhesion force of the elytra were evaluated using contact angle measurement device and force transducer, respectively. The results show that the microstructure of the elytra changed greatly after different chemical treatments and the changes in wettability were mainly related to the changes of elytra roughness after treatments. The differences in adhesion force between differently treated elytra and wet sand indicate that the molecular polarity of the elytral surface is decisive for its anti-adhesive (self-cleaning) property.

Variation of Goliathus orientalis (Moser, 1909) Elytra Nanostructurations and Their Impact on Wettability

“…The elytra were then washed in ethanol and dried. Most of the surface secretions have been described as hardly soluble in ethanol [27]. However, to verify this claim, native elytra were also observed as control samples and produced the same results (data not shown).…”

“…This precise combination of static and dynamic wetting behavior is also known as the petal effect in the literature [18,19,20,21]. This property is often exploited in nature when water harvesting and collection is necessary for survival [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36].…”

“…For insects, in order to control their wettability, they must simultaneously take advantage of two parameters: their surface energy and their surface morphology. The surface energy is typically altered via variation of the natural surface composition (i.e., wax cement), or the epicuticular secretion of different species [27]. Concerning the second parameter, varied surface morphologies have been reported to have a significant influence over wettability.…”

Research on the typical microstructures and contact angles of hydrophobic plant leaves

“…Provided good coverage of epicuticular waxes on the leaf surface, the intrinsic contact angle for the second-layer structure (nanoprotrusions) is set as 105°. Then the θ r2 value is calculated as 127.11°using (7). Subsequently, inserting values of f s1 (0.696) and θ r2 (127.11°) into (1), the apparent angle for the Loropetalum chinense leaf (θ r ) is computed as 136.84°.…”

“…Hydrophobic and superhydrophobic phenomena have been frequently observed in nature, such as hydrophobic beetle cuticle surface [7], hydrophobic bamboo leaf [8], water‐repellent rose petal [9], water‐walking strider [10] and water‐transporting cactus [11]. For the past few decades, significant efforts have been devoted to designing and fabricating artificial materials by mimicking features of natural surfaces [12, 13].…”