Two- and Three-Dimensional Ultrastructures of the Micron-Scale Adhesive Setae of a Leaf Beetle Chrysochus chinensis (Coleoptera: Chrysomelidae)1

(Baly) (Chrysomelidae: Eumolpinae) is a phytophagous leaf beetle that excels in climbing on its host plants’ leaf surfaces and has well-developed adhesive setae on its feet. Using scanning electron microscopy, we examined the ultrastructure of the adhesive setae and recognized three types of setae, namely pointed, spatulate, and discoidal. The terminal plate areas of the three types of setae were 7.59 ± 1.76 μm2, 41.16 ± 1.46 μm2, and 63.65 ± 2.35 μm2, respectively. The three-dimensional topography of the terminal plates of three types of setae were imaged with an atomic force microscope. We found that the terminal plate of the discoidal seta had a concave center and a high circular edge, and the edge was 200–400 nm higher than the center. The ventral side of the spatulate seta was smooth with a 200-nm-high edge at two sides of the terminal plate. The results showed that the discoidal seta had the biggest terminal plate area (63.65 ± 2.35 μm2) and its topography can gather liquid and produce a 200- to 400-nm-thick fluid film between the terminal plate and smooth substrates. With the help of capillary force of the tarsal secretion, it can enhance adhesion force. The function of the discoidal seta, which is only present on male beetles, is hypothesized to serve for strong attachment force during mating.