Abstract
Plant surfaces showing hierarchical structuring are frequently found in plant organs such as leaves, petals, fruits and stems. In our study we focus on the level of cell shape and on the level of superimposed microstructuring, leading to hierarchical surfaces if both levels are present. While it has been shown that epicuticular wax crystals and cuticular folds strongly reduce insect attachment, and that smooth papillate epidermal cells in petals improve the grip of pollinators, the impact of hierarchical surface structuring of plant surfaces possessing convex or papillate cells on insect attachment remains unclear. We performed traction experiments with male Colorado potato beetles on nine different plant surfaces with different structures. The selected plant surfaces showed epidermal cells with either tabular, convex or papillate cell shape, covered either with flat films of wax, epicuticular wax crystals or with cuticular folds. On surfaces possessing either superimposed wax crystals or cuticular folds we found traction forces to be almost one order of magnitude lower than on surfaces covered only with flat films of wax. Independent of superimposed microstructures we found that convex and papillate epidermal cell shapes slightly enhance the attachment ability of the beetles. Thus, in plant surfaces, cell shape and superimposed microstructuring yield contrary effects on the attachment of the Colorado potato beetle, with convex or papillate cells enhancing attachment and both wax crystals or cuticular folds reducing attachment. However, the overall magnitude of traction force mainly depends on the presence or absence of superimposed microstructuring.
Highlights
In plants the cuticle constitutes the outermost layer of the plant body and provides the direct interface to the environment
While it has been shown that epicuticular wax crystals and cuticular folds strongly reduce insect attachment, and that smooth papillate epidermal cells in petals improve the grip of pollinators, the impact of hierarchical surface structuring of plant surfaces possessing convex or papillate cells on insect attachment remains unclear
Independent of superimposed microstructures we found that convex and papillate epidermal cell shapes slightly enhance the attachment ability of the beetles
Summary
In plants the cuticle constitutes the outermost layer of the plant body and provides the direct interface to the environment. The cuticle can provide protection against harmful radiation, influences the optical properties of the plant surface, and can either improve or impede attachment of insects [1,2]. Structuring of epidermal surfaces such as leaves, petals and stems is manifold and occurs on different levels, leading to hierarchical organisation [3]. Both the shape and orientation of surface structuring have been described and named by Barthlott and co-workers [4,5] and in the review of Koch et al [1]. In the present study we focus on the cellular level (shape of epidermal cells) and on the level of superimposed microstructuring, such as wax crystals (wc), cuticular folds (cf), or only films of wax (o)
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