Interaction of liquid epicuticular hydrocarbons and tarsal adhesive secretion in Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)

Species of various insect orders possess specialised tarsal adhesive structures covered by a thin liquid film, which is deposited in the form of footprints. This adhesive liquid has been suggested to be chemically and physiologically related to the epicuticular lipid layer, which naturally covers the body of insects and acts as the prime barrier to environmental stresses, such as desiccation. The functional efficiency of the layer, however, is jeopardised by partial melting that may occur at physiological temperatures. In this study, light microscopic images of elytral prints show that the epicuticular lipid layer of the Colorado potato beetle Leptinotarsa decemlineata actually is partially liquid and chemical investigations reveal the high similarity of the epicuticular hydrocarbon pattern and the tarsal liquid. By means of chemical manipulation of the surface hydrocarbon composition of live beetles, the substance exchange between their tarsal adhesive hairs and the body surface is monitored. Histological sections of L. decemlineata tarsi, furthermore, reveal glandular cells connected to individual adhesive setae and departing from these results, an idea of a general mechanism of tarsal secretion is developed and discussed in a functional-ecological context.