Contribution of different tarsal attachment devices to the overall attachment ability of the stink bug Nezara viridula

Abstract

The tarsal attachment devices of the southern green stink bug Nezara viridula, a cosmopolitan pest of different crops, encompass a pair of claws, distal pretarsal smooth pulvilli, and a proximal hairy pad on the ventral basitarsus. To evaluate the role of these attachment devices in generating attachment, behavioural experiments testing locomotion of insects with ablated pulvilli, shaved hairs and cut-off claws were performed. Using traction force experiments, insect attachment performance was evaluated on artificial substrates characterised by different roughness and on two substrates with different surface energies in the air and under water. To examine the contact area of attachment devices during resting, pulling and inverted walking, intact insects and those without claws were video-recorded using a high-speed camera. The present data reveal a great involvement of pulvilli in insect attachment on all the tested surfaces, while the hairy pad seems to have a role in producing friction forces only on smooth surfaces and on surfaces with intermediate roughness. The hairy pad was revealed to be important in adhesion to hydrophobic substrates under water, a function that could be relevant for N. viridula insects in consideration that many plant leaves tend to have hydrophobic surfaces and may be often covered by water film.

Gripping ease in southern green stink bugsNezara viridulaL. (Heteroptera: Pentatomidae): Coping with geometry, orientation and surface wettability of substrate

“…In addition, they were reported to produce friction forces on horizontal, flat smooth surfaces or surfaces with intermediate roughness in N. viridula (Salerno et al . ). The morphology and dimensions of setae with flattened lanceolate terminals in N. viridula resemble tarsal adhesive setae in leaf beetles (Chrysomelidae) and representatives of other families of Coleoptera (Stork ; Voigt et al .…”

“…, Salerno et al . ), although males are smaller (6–8 mm) than females (12–16 mm) (Heerden ). This is in accordance with the copulation posture where both male and female attach their feet to the substrate during mating, facing in opposite directions and achieving the genital linkage only by abdominal tips (Drake ; Mitchell & Mau ; Kon et al .…”

“…These fleshy pads, arising from pretarsi, are present in nearly all pentatomorphans, and have been previously studied in detail for several species (Goel & Schaefer 1970;Slater 1973;Schuh 1976;Ghazi-Bayat 1979;Ghazi-Bayat & Hasenfuss 1980a,b, 1981Gorb & Gorb 2004). Tarsal ultrastructural analysis in N. viridula illustrated the flexible nature of pulvilli caused by a large portion of resilin, indicating the adaptability to a wide range of substrate topographies (Rebora et al 2018, Salerno et al 2018a.…”

“…Recent studies have shown the attachment ability of adult N. viridula to various leaf surfaces and hydrophilic (water attractive) glass, as well as smooth and rough hydrophobic (water repellent) epoxy resin (Salerno et al . , ,b; Voigt et al . ; see notes below Table S1 for explanation of surface wettability).…”

“…Recent studies have shown the attachment ability of adult N. viridula to various leaf surfaces and hydrophilic (water attractive) glass, as well as smooth and rough hydrophobic (water repellent) epoxy resin (Salerno et al 2017(Salerno et al , 2018aVoigt et al 2018; see notes below Table S1 for explanation of surface wettability). Curved, tapered, 50-μm-long claws were found to interlock with fibrillar structures and with surface irregularities larger than 2.5 μm.…”