Multifunctional Adhesives on the Eggs of the Leaf Insect Phyllium philippinicum (Phasmatodea: Phylliidae): Solvent Influence and Biomimetic Implications

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.

Resolving a century-old case of generic mistaken identity: polyphyly of Chitoniscus sensu lato resolved with the description of the endemic New Caledonia Trolicaphyllium gen. nov. (Phasmatodea, Phylliidae)

“…The exochorionic pinnae of the eggs of Phyllium philippinicum are involved in a water responding adhesive system that attaches the eggs to different surfaces (Büscher et al 2020b). Similar fringe-like expansions on their egg shells are reported for other phylliid eggs and hypothesized to be involved in adhesion as well (Büscher et al 2020c). Due to their similarity in morphology, it is highly likely that the eggs of Chitoniscus sensu stricto provide the same adhesive capability.…”

The exceptional attachment ability of the ectoparasitic bee louse Braula coeca (Diptera, Braulidae) on the honeybee

“…In the case of B. coeca , it uses a temporary attachment system that enables easy attachment/detachment to/from the surface and fast movement on the host. Other organisms that reach such high safety factors normally rely on glues and attach permanently to a surface (e.g., barnacles, tubeworms or mussels: Oliveira & Granhag, 2016; or insect eggs: Büscher, Quigley & Gorb, 2020; Büscher, Lohar, et al 2020). The high attachment forces reached by the bee lice are very likely a result of the host specialization.…”

Oviposition site selection and attachment ability of Propylea quatuordecimpunctata and Harmonia axyridis from the egg to the adult stage

“…2i), which was also described for the egg adhesive of the leaf insect Phyllium philippinicum Hennemann et al . (Phasmatodea: Phylliidae) (Büscher et al ., 2020a, b). In other studies, testing insect egg attachment such as of the codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) to fruit and leaf surfaces of different apple cultivars (Al Bitar et al ., 2012, 2014), stronger forces were recorded to detach the eggs from the lower leaf side compared with those from the upper leaf side.…”