Jumping without slipping: leafhoppers (Hemiptera: Cicadellidae) possess special tarsal structures for jumping from smooth surfaces

Abstract

Many hemipteran bugs can jump explosively from plant substrates, which can be very smooth. We therefore analysed the jumping performance of froghoppers (Philaenus spumarius, Aphrophoridae) and leafhoppers (Aphrodes bicinctus/makarovi, Cicadellidae) taking off from smooth (glass) and rough (sandpaper, 30 µm asperity size) surfaces. On glass, the propulsive hind legs of Philaenus froghoppers slipped, resulting in uncontrolled jumps with a fast forward spin, a steeper angle and only a quarter of the velocity compared with jumps from rough surfaces. By contrast, Aphrodes leafhoppers took off without their propulsive hind legs slipping, and reached low take-off angles and high velocities on both substrates. This difference in jumping ability from smooth surfaces can be explained not only by the lower acceleration of the long-legged leafhoppers, but also by the presence of 2–9 soft pad-like structures (platellae) on their hind tarsi, which are absent in froghoppers. High-speed videos of jumping showed that platellae contact the surface briefly (approx. 3 ms) during the acceleration phase. Friction force measurements on individual hind tarsi on glass revealed that at low sliding speeds, both pushing and pulling forces were small, and insufficient to explain the recorded jumps. Only when the tarsi were pushed with higher velocities did the contact area of the platellae increase markedly, and high friction forces were produced, consistent with the observed jumps. Our findings show that leafhoppers have special adhesive footpads for jumping from smooth surfaces, which achieve firm grip and rapid control of attachment/detachment by combining anisotropic friction with velocity dependence.

Froghoppers jump from smooth plant surfaces by piercing them with sharp spines

“…They use claws and spines to interlock with asperities on rough surfaces, and soft adhesive pads to cling to smooth substrates (27). Many insects also possess special "heel" pads on the tarsus that produce high friction when pressed against the substrate (12,(28)(29)(30). Our study shows that insects can use a fundamentally different mechanism to grip on smooth plant surfaces.…”

“…When P. spumarius froghoppers jumped from smooth glass surfaces, their hind legs always slipped, resulting in steep jumps with a rapid forward spin and a low takeoff velocity (Movie S1 and ref. 12). By contrast, P. spumarius froghoppers never slipped when jumping from smooth epoxy, resulting in fast jumps with a low takeoff angle (Movie S2).…”

“…Moreover, when Philaenus froghoppers slip on glass, most of the energy of the jump is dissipated by the rapid slipping and kicking of the hind legs. The body's kinetic energy is more than ninefold reduced (12), and the fourfold smaller takeoff velocity may result in a proportional reduction in the pressure at the center of the spines (ca. 0.6 GPa to 0.8 GPa).…”

“…Strong grip and highly dynamic surface attachment are particularly important for animals which jump to escape from predators or rapidly move through complex environments, and the action of jumping brings unique biomechanical challenges. Consequently, studying jumping animals may reveal novel solutions to biomechanical problems (11), and can also provide new insights into attachment mechanisms (12).…”

“…In a previous study, we showed that Aphrodes bicinctus/makarovi leafhoppers were able to jump from smooth glass substrates by briefly bringing some soft tarsal pads (platellae) on their hind legs into surface contact during the acceleration phase of the jump (12). In contrast, froghoppers such as P. spumarius lack soft platellae on their hind legs; they slipped when attempting to jump from glass, resulting in uncontrolled upward jumps with a rapid forward spin (12,23). How, therefore, do froghoppers jump successfully from the plants on which they live?…”