Microstructure of the biological attachment devices in the ladybug Harmonia axyridis (Coleoptera: Coccinellidae)

Biological attachment device is optimized in insect legs for attachment onto the variety of natural substrate. We have studied the microstructural characteristics of the tarsal appendages in the ladybug Harmonia axyridis using scanning electron microscopy to reveal the attachment system of their legs. The attachment devices are composed of claws and adhesive pads. The claws are connected with pretarsal segment, and their apical diverged hooks are developed to hold rough substrates. In contrast, the adhesive pads have an adhesive function onto smooth surface. The pads are interspersed at the ventral part of each tarsomere, and are composed of two kinds of hairy setae. The discoid tip seta (DtS) has a spoon-shaped endplate usually with a rounded concave structure, whereas the pointed tip seta (PtS) has a pointed tip, usually with a hooked endplate. While the PtS is broadly localized concentrically on the marginal area of both the proximal and distal pads, the DtS can be seen at the central areas of each adhesive pad except for the hind legs. Our findings demonstrate the presence of the direction-dependence pattern of the fibrillar system as well as a functional modification of the tenent setae to achieve proper contact with almost any kind of substrates.