Tarsal structures of beetles adhere to plant surfaces by secreting lipids that are liquid at normal temperatures.

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The Colorado potato beetle must defy gravity when climbing up vertical stems of its host plant. It solves this challenge with the help of specialized tarsal structures coated with a thin film of liquid wax similar to the protective wax on other parts of the beetle's body that keep it properly hydrated. The protective wax is solid at ambient temperatures to form a more stable coating, but liquid on the adhesive structures to more effectively interact with the climbing surface.

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"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." (Geiselhardt et al. 2010:369)

“[R]esults suggest the chemical similarity of the epicuticular lipid layer and tarsal secretion to be based on continuous exchange and provisioning from a possibly common substance pool. The suggested presence of specialised tarsal glands, however, calls for some sort of adaptation of the adhesive liquid that generates attachment forces based on the viscosity and surface tension. This might be either an increased amount of secretion to encounter the liquid loss during walking or a chemical fine tuning to locally permit a liquidity which would be undesirable on other body parts. Thus, the need for a sufficient amount of adhesive or lubricating superficial liquid may be one explanation as to why many insects have epicuticular lipids which melt at physiological temperatures, despite the risk of lethal water loss." (Geiselhardt et al. 2010:376)

"[A]dhesive organs require a thin film of liquid to generate attachment forces by compensating nanoscale surface irregularities. Forces are suggested to be based on physicochemical properties of the liquid film and its interaction with the wetted surfaces and therefore should depend on the chemical composition of the liquid...cuticular components were detected with carbon backbones ranging from C20 to C39...[and] are characteristic for insect cuticular lipids...[Therefore, p]ossibly, this is not only true for beetles, but also for representatives of other insect orders with adhesive liquids." (Geiselhardt et al. 2011:181-185)

Journal article
Interaction of liquid epicuticular hydrocarbons and tarsal adhesive secretion in Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)J Comp Physiol AApril 1, 2010
Stefanie F. Geiselhardt, Stefan Lamm, Claudia Gack, Klaus Peschke

Journal article
Congruence of epicuticular hydrocarbons and tarsal secretions as a principle in beetlesChemoecologyApril 16, 2011
Stefanie F. Geiselhardt, Sven Geiselhardt, Klaus Peschke

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Colorado Potato BeetleLeptinotarsa decemlineataSpecies

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