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.
Highlights
Many insects jump to escape from predators, to move in complex terrain or to launch into flight
Our results show that Philaenus froghoppers and Aphrodes leafhoppers differ in their ability to jump from smooth surfaces
Leafhoppers never slipped and jumped with similar take-off velocities and angles from both glass and sandpaper. This difference in jumping ability from smooth surfaces can be explained by the different pushing forces produced by both insects, and by the presence of specialized structures called platellae on the hind tarsi of leafhoppers, which are absent in froghoppers
Summary
Many insects jump to escape from predators, to move in complex terrain or to launch into flight. In contrast to insects with very long hind legs that power their jumps mainly by direct muscle action (e.g. bush crickets, [8]), jumping Auchenorrhyncha have shorter hind legs and employ catapult mechanisms to propel themselves off the ground [9,10,11,12,13,14]. Many jumping hemipteran and orthopteran insects are generalist herbivores that live and feed on multiple species of plants [15,16], which can have microscopically smooth surfaces [17,18]. To jump forward, they have to produce high forces parallel to the ground.
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