Attachment to plant surface waxes by an insect predator.

Insects foraging on plant surfaces must attach to the layer of lipophilic materials known as epicuticular waxes (EW) that cover these surfaces. In this paper, we briefly review the evidence that variation in EW morphology can influence the ecology of herbivorous insects directly, by affecting their attachment to plant surfaces, and indirectly by affecting attachment by actively foraging predatory insects to plant surfaces. We then present new data examining how EW micromorphology and chemical composition of Brassica oleracea influence attachment by the predatory beetle, Hippodamia convergens (Coccinellidae). Bioassays with genotypes of B. oleracea differing in wax characteristics, and with EW extracts from these plants applied to glass, show that wax crystals disrupt attachment. In addition, bioassays show that attachment by H. convergens differs among EW extracts prepared to have smooth surfaces without crystals. The differences in attachment under these conditions are evidently due to the chemical composition of the waxes. Bioassays with two pure wax constituents show that wax composition can significantly affect attachment by H. convergens. The study opens the way for using a similar approach to understand attachment by insects to waxy plant surfaces.