GLOBE THISTLES AND BRYOCORINAE MIRID BUGS: OVERCOMING HAIRY PLANT SURFACES
Bryocorinae species (Heteroptera, Miridae) live omnivorously, also feeding on agricultural pest arthropods. Those bugs' particular ability to hold and walk on hairy plant terrains has already been reported in the 1960s and was first explored in detail by Southwood in 1986 (Overview on plant surfaces and insects; Edward Arnold Publishers, London). Our later studies turned out different strategies depending on the species. While larger and heavier South-African Pameridea roridulae use a thick epicuticular grease and strong movements to escape from the deadly sticky flypaper of carnivorous dewplants (defense strategy), the thin and narrow palearctic Dicyphus errans holds its body at a large distance to the hairy substrate and uses particular slim, slender legs and sheppard-hook-shaped claws to stalk along trichomes (avoidance strategy; see "Locomotion in a sticky terrain "by Voigt & Gorb 2010).
Our present study elucidates that further nuances exist between related species, Macrolophus pygmaeus and Dicyphus errans, both using the avoidance strategy. We explored the macro and micro morphology of different Echinops species and accessions, as well as the attachment of Macrolophus pygmaeus to three selected species. Globe thistles impress with their complex growth, diversity of hairs, particularly the abaxially dense felt-like hairy layer, epicuticular waxes and folds, covering the plant surface. Thus, they provide suitable habitat and shelters for arthropods; they are recommendable banker plants. Macrolophus pygmaeus can occur in a remarkable abundance in Echinops crops. Bugs generated 47 times their own body weight when attaching to Echinops plants. They adhere more strongly to abaxial leaves than to less hairy adaxial ones; on glandular hairy surfaces, they move more gently.
These aspects should be considered in evolutionary and biocontrol approaches, knowing that insects' foothold on plant substrates matters for life history and prey consumption (Voigt 2019).
Similar to other leaf beetles (Coleoptera, Chrysome-lidae), Diabrotica virgifera virgifera beetles possess tarsal adhesive setae, facilitating foothold and locomotion on various substrates, including maize host plants. However, the male-specific setae in this species, adhering to female's back, are unique (so far observed). Two seta types occur on male feet: (1) long ones with ovoid, slightly tapered terminals and basically connected shafts and (2) short ones with round terminals and centrally connected shafts. They are densely packed, forming a hexagonal pattern. The latter are indeed mushroom-shaped – as suggested for (not mushroom-shaped) male-specific setae in other beetles so far, and provide excellent models inspiring biomimetic adhesives with mushroom-shaped structures. See our recent article for details and enjoyment …
