Gripping ease in southern green stink bugs Nezara viridula L. (Heteroptera: Pentatomidae): Coping with geometry, orientation and surface wettability of substrate

Abstract

The southern green stink bug Nezara viridula L. (Heteroptera, Pentatomidae) is highly polyphagous, preferring apically situated seeds and fruits on more than 150 plant species belonging to over 30 plant families all over the world. This forces them to move over highly variable terrains, including plant stems, leaves, pods and buds, which requires efficient attachment. Stink bugs have long slender legs and feet (tarsi) equipped with paired curved claws, paired soft adhesive pads (pulvilli), and flattened lanceolate hairs (setae), which arise ventrally on the first and second foot segments (tarsomeres). To characterize their attachment abilities on well‐defined test substrates, here we comparatively measured and analyzed the traction forces of bugs walking horizontally and vertically on hydrophilic (water attractive) and hydrophobic (water repellent) glass plates and rods. The latter correspond to the geometry of preferred feeding sites of stink bugs in the field. The results show a clear contribution of tarsal flattened lanceolate hairs to the stink bug's attachment. Higher traction forces are generated on a glass rod than on a glass plate, corresponding to up to individual maximum of 43 times the stink bug's body weight. Substrate hydrophobicity promotes the attachment, while the measured forces are up to eight times lower when tarsal hairs are disabled. The combination of smooth and hairy tarsal pads results in a remarkable attachment ability, which enables N. viridula to climb unstable apical plant parts, and supports their invasive behavior and global dispersion.

Attachment Performance of Stick Insects (Phasmatodea) on Plant Leaves with Different Surface Characteristics

“…Phasmids already showed an increased pull-off force on curved artificial substrates, if compared to flat surfaces [ 38 ]. Similar effects have been observed in other insects [ 41 , 42 , 43 , 44 , 45 ] and frogs [ 46 , 47 ]. In contrast to all other leaves on which the phasmids engaged the arolium only during the pull-off measurement, and similar to the individuals measured on flat artificial substrates in Büscher and Gorb [ 26 ], some individuals brought their euplantulae into contact during the pull-off measurement on H. ghiesbreghtii .…”

Attachment performance of stick insects (Phasmatodea) on convex substrates

“…Referring to the results of this study, this induces a much more complex interaction of various phenomena. The results presented herein further stress the importance of evaluation of attachment performance on different surface geometries (Gladun and Gorb 2007;Bußhardt et al, 2014;Voigt et al, 2017Voigt et al, , 2019, besides commonly investigated flat substrates. Furthermore, insights generated from the present experiments on curved substrates can be potentially useful for the design of bioinspired robotic grippers (e.g.…”

“…Studies of different insect species walking on thin stems revealed several strategies of attachment, including the use of pads, claws and additional structures on the tibia enabling attachment to and propulsion along the stems (Gladun and Gorb, 2007;Bußhardt et al, 2014). Measurements of attachment forces showed remarkable differences between the maximal forces on curved surfaces and flat ones for beetles and true bugs (Bußhardt et al, 2014;Voigt et al, 2017Voigt et al, , 2019. In these studies, the measured attachment forces were higher on rods in comparison to flat plates of the same material.…”

Attachment devices and the tarsal gland of the bug Coreus marginatus (Hemiptera: Coreidae)

“…Smooth pulvilli and basitarsal hairs, together with claws, represent the tarsal attachment devices of the coreid bug C. marginatus. Traction force experiments on the pentatomid bug N. viridula (whose attachment devices are similar to C. marginatus) with ablated pulvilli, shaved hairs and cut-off claws (Salerno et al 2018) revealed a great involvement of pulvilli in insect attachment on horizontal smooth and rough surfaces; while, the hairy pad, with its resilin-bearing flexible tips as previously shown for N. viridula (Rebora et al 2018), seems to be important in attachment to horizontal hydrophobic substrates under water (Salerno et al 2018) and on vertical smooth roads as well (Voigt et al 2019).…”