Ontogenesis of the attachment ability in the bug Coreus marginatus (Heteroptera, Insecta)

Each tarsus of Coreus marginatus L. (Coreidae) bears a pair of smooth flexible pulvilli adapted for attachment to relatively smooth surfaces, such as their host plant Rumex crispus L. (Polygonaceae). This account quantifies insect attachment abilities on smooth surfaces at various stages of ontogenesis. Friction (shear) force (FF) of adults and juvenile insects was measured by the use of a computer controlled centrifugal force tester equipped with a fibre optical sensor. Pad area, body size and body mass were determined individually for each experimental insect. Light microscopy revealed no difference in pulvilli area between different leg pairs. Pulvilli area demonstrated a stronger increase with increasing linear dimensions, as predicted by scaling laws. Since friction coefficient (relationship between FF and body weight) (FC) was always higher than 1, it was concluded that adhesion has strongly contributed to the measured friction. The frictional properties of pulvilli do not change during ontogenesis. Thus, only the growth of pulvilli and, therefore, the increased contact area, contribute to the increasing attachment ability in insects at later larval stages. Due to different scaling of the body mass and area of attachment organs, smaller insects attach relatively more strongly. Both FF and FC were higher in experiments in which higher angular acceleration (AC) was applied. Lateral tenacity determined individually for experimental insects and pooled for all animals and accelerations is 0.097 N m(-2). These data led us to suggest that viscosity of the pad secretion and/or visco-elastic properties of the foam-like material of pulvilli play an important role in the attachment ability of insects.