Plant surface-bug interactions: Dicyphus errans stalking along trichomes

In contrast to many arthropods whose locomotion on plant surfaces is impeded by trichomes, the omnivorous mirid bug Dicyphus errans Wolff (Heteroptera, Miridae, Bryocorinae) lives on pubescent plants and preys on a variety of phytophagous arthropods. Morphological (slim body, long slender legs, elongated curved claws) and behavioural (locomotion) adaptations to hairy plant substrates result in higher predation effectiveness and fecundity, as well as a shorter developmental cycle of the bug compared to insects on plants without trichomes. To understand the bug-plant interactions from the biomechanical point of view, the bug's attachment system and the leaf surfaces of various plant species were analysed. Bug attachment ability was estimated in an inversion experiment on the adaxial and abaxial sides of leaves in 40 plant species. Furthermore, bug traction forces on the abaxial leaf side of 14 plant species were measured. Morphometrical variables of trichomes and the adhesive properties of plant surfaces were estimated. The bugs' traction force ranged from 0.07 mN on Brassica oleracea (Brassicaceae) to 1.21 mN on Plectranthus ambiguus (Lamiaceae) and Solanum melongena (Solanaceae). Bugs performed considerably better on hairy surfaces where a significant positive correlation between the force and both the trichome length and diameter was found. The trichome density and aspect ratio did not influence the force. Adhesion properties of plant surfaces covered with trichomes may also significantly impede the traction force. Based on the results obtained, it is concluded that hairy plants provide a more suitable environment for D. errans than either smooth ones or those covered with wax crystals. Hairy plant surfaces are predicted to support stronger attachment and therefore more reliable locomotion of the bug.