Plant-dwelling beetles overcome challenging attachment hurdles by means of ellaborated, tarsal attachment devices, which are frequently equipped with hairy adhesive pads. While the tarsal functional morphology has been intensively studied in leaf and ladybird beetles during the last decades, longhorn beetles (Cerambycidae) have been widely neglected in experimental studies on insect attachment. However, they are known to strongly hold on to plant substrates, using tarsi that are densely covered with adhesive setae. In the present study, we examined the Japanese pine sawyer beetle, Monochamus alternatus, which lives in an arboreal habitat, as an exemplary case. Traction force of male and female beetles on (1) flat and (2) cylindrical, rod-shaped glass was measured. The substrates are further called (1) glass plate and (2) glass rod. Both male and female M. alternatus bear ribbon-shaped tarsal adhesive setae with broadened, ultrathin terminals. They release a distinct amount of adhesion-mediating fluid after each step. The beetles never walked on the vertically oriented glass plate. However, they performed well on the horizontal plate, as well as on the horizontally and vertically oriented glass rod. Males generated higher forces and safety factors (traction force devided by the body weight) than females, reaching up to 206 mN traction force and a safety factor of 32 on the horizontal glass rod. Thus, they are able to carry their remarkable body weight (ca. 300 mg) throughout a rather long life span. We assume the adaptation of M. alternatus to the attachment on convex and rod-shaped structures to be present in its natural habitat. This longhorn beetle species achieves a proper hold through a combination of interacting parameters: appropriate body alignment and two-sided leg grasping, and generation of normal and friction forces by tarsal pads. This smart attachment system gives rise to the reconsideration of the ecological and evolutionary background, and provides insights for the development of bio-inspired technical grippers.

Distribution and electrophysiological responses of contact chemosensilla were examined in the Aristolochiaceae-feeding butterfly Atrophaneuraalcinous. In adult butterflies, tarsal contact chemosensilla of the foreleg were classified into two groups based on length: long- and short-type sensilla. Long-type sensilla were distributed much more widely in females than in males, whereas short-type sensilla were found at the edge of the tarsi in a similar manner in both sexes. Taste responses of the long- and short-type sensilla to methanol extracts of Aristolochia debilis and Citrus spp. were recorded. Aristolochia debilis extracts evoked spikes with different amplitudes, whereas Citrus spp. extracts evoked spikes with a single amplitude in the long-type sensilla. Short-type sensilla did not respond to either extract. Moreover, we recorded responses to different concentrations of sucrose and NaCl. Results suggest that adult butterflies can discriminate the taste of host plant components from other chemicals using long-type sensilla during oviposition and may recognize diets containing sugar and salts during feeding using short-type sensilla. In the larval mouthparts, there were lateral and medial styloconic sensilla on the maxillary galea and epipharyngeal sensillum on the epipharynx. Electrophysiological responses of these sensilla suggest that larvae can discriminate between host plant compounds.