Plant surfaces with cuticular folds and their replicas: influence of microstructuring and surface chemistry on the attachment of a leaf beetle.

Plant surfaces covered either with epicuticular wax crystals or cuticular folds have been shown to strongly reduce the ability of insects to attach to them. However, the relative impact of surface structuring vs. surface chemistry on insect attachment remains unclear. To understand the mechanisms reducing adhesion of insects on plant surfaces in more detail, we performed traction experiments (i) on plant surfaces covered with cuticular folds of different dimensions, and on their (ii) untreated and (iii) hydrophobized replicas. As a reference, measurements were performed on replicas of smooth plant surfaces and of glass. Traction forces were measured with a highly sensitive force transducer, using tethered male Colorado potato beetles (Leptinotarsa decemlineata) as a model insect species. Contact angle measurements with water and diiodomethane were also performed to examine the physicochemical properties of the test surfaces. We found that surface structuring has a strong influence on the magnitude of the attachment force. In contrast, under the chosen experimental conditions, surface chemistry had no significant influence. Our results indicate that attachment of the beetles is reduced solely by the dimensions of the folds, with cuticular folds of about 0.5 μm in both height and width being the most effective. Contrary to the attachment of beetles, the wettability of the surfaces was considerably influenced by both surface structuring and chemistry. These results contribute to a better understanding of plant-insect interactions and the function of microstructured surfaces, and may facilitate the development of biomimetic anti-adhesive surfaces.