Abstract

Many plant-sap sucking bugs of the order Hemiptera are able to perform explosive jumps. As most hemipterans live on plant surfaces, which can be smooth, we studied whether and how these insects are capable of taking off from smooth substrates. We compared jumps of froghoppers (Philaenus spumarius, Aphrophoridae) and leafhoppers (Aphrodes bicinctus/makarovi, Cicadellidae) on smooth glass and rough sandpaper (30 μm asperity size). While Philaenus froghoppers were unable to perform controlled jumps on glass because their hind legs slipped extensively, Aphrodes leafhoppers took off normally without slipping. On glass, froghoppers jumped mainly upward and four times more slowly than on the rough substrate, whereas leafhoppers jumped with similar take-off angles and velocities on both substrates. High-speed microscopy of hind tarsi of Aphrodes jumping from glass revealed that 2-9 soft structures per leg (`platellae', present in leafhoppers but not froghoppers) contacted the surface extremely brief (3 ms) during take-off. To test whether these structures can produce sucient traction for forward jumps, we measured friction forces of individual tarsi on glass. When sliding slowly, shear forces were small for both pushing and pulling, and insucient to explain the recorded low take-off angles. Only when the tarsi were pushed with larger velocities did the contact areas increase strongly, and friction coecients were high enough to explain the observed jumps. Our findings demonstrate that insects have evolved special tarsal structures for jumping from smooth surfaces, which achieve extraordinarily rapid control of attachment and detachment by combining directional friction with velocity-dependence.