Abstract
Leaf insects (Phylliidae) are well-camouflaged terrestrial herbivores. They imitate leaves of plants almost perfectly and even their eggs resemble seeds—visually and regarding to dispersal mechanisms. The eggs of the leaf insect Phyllium philippinicum utilize an adhesive system with a combination of glue, which can be reversibly activated through water contact and a water-responding framework of reinforcing fibers that facilitates their adjustment to substrate asperities and real contact area enhancement. So far, the chemical composition of this glue remains unknown. To evaluate functional aspects of the glue–solvent interaction, we tested the effects of a broad array of chemical solvents on the glue activation and measured corresponding adhesive forces. Based on these experiments, our results let us assume a proteinaceous nature of the glue with different functional chemical subunits, which enable bonding of the glue to both the surface of the egg and the unpredictable substrate. Some chemicals inhibited adhesion, but the deactivation was always reversible by water-contact and in some cases yielded even higher adhesive forces. The combination of glue and fibers also enables retaining the adhesive on the egg, even if detached from the egg’s surface. The gained insights into this versatile bioadhesive system could hereafter inspire further biomimetic adhesives.
Highlights
Phasmids— called stick and leaf insects—render proof for a highly connected co-evolution between these herbivore insects and plants
To evaluate the effects of the solvents on the morphology of the exochorionic extensions of the eggs and the glue coverage, we examined the adhesive system of the eggs using scanning electron microscopy (SEM)
The adhesive system of P. philippinicum consists of two main components: the pinnae and the glue
Summary
Phasmids— called stick and leaf insects—render proof for a highly connected co-evolution between these herbivore insects and plants. Different aspects of their morphology and physiology, e.g., cryptic masquerade [1,2], oviposition [2,3,4,5,6], as well as their elaborate tarsal attachment systems [7,8,9,10], substantiate this assertion. Very well-known examples for this aspect of phasmatodean evolution are the Walking Leaves (Phyllidae) These insects perfectly imitate leaves of plants and blend with their environment [11,12,13]. In the subsequent radiation of angiosperms, both plants and stick insects evolved foliaceous forms, a result of the imitation of the plants by stick insects and leaf insects
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