Abstract
The tarsal attachment system of the Madagascar Hissing cockroach Grompadorhinaportentosa (Blattodea, Blaberidae) was analysed with respect to the ultrastructure of its smooth adhesive pads (arolium, euplantula), the chemical composition of its adhesive secretion, and its adhesion and friction performance on surfaces of different roughnesses. Local measurements performed with a nanotribometer showed that, in the non-manipulated euplantulae, friction was clearly increased in the push direction, whereas the arolium of the fore tarsus showed higher friction in the pull direction. The surface of the euplantulae shows an imbricate appearance, whereby the ledges face distally, which might contribute to the observed frictional anisotropyin push direction. The glandular epithelium of both the arolium and the euplantulum releases adhesive secretions into a subcuticular void from which it has to permeate the thick cuticle of the adhesive pads. In the euplantulae, adhesion was one to two orders of magnitude lower than friction. Whereas adhesive tenacity was slightly decreased with depleted secretion, it was considerably increased after artificial application of oily liquids. Our chemical analyses of the secretion suggest a semisolid consistency of the adhesive secretion, which probably facilitates the detachment of the tarsus during locomotion. On nanorough surfaces, the insect appears to benefit from employing emulsions instead of pure oils to avoid excessive friction. Based on our chemical analyses, 12 synthetic heterogeneous adhesive emulsions were prepared. By varying their chemical composition, they could be adjusted to have diverse consistencies. Some of them were able to mimic certain rheological and tribological properties of natural tarsal insect adhesives.