Dagmar Voigt

Attachment of honeybees and greenbottle flies to petal surfaces

Flower surfaces play a key role in the interaction with pollinators acting as signals and landing sites to attach to. To test attachment, Carniolan honeybees and greenbottle flies were used. Both species represent pollinators equipped with smooth or hairy tarsal attachment devices, respectively. A combination of microscopic methods and traction force measurements was applied in order to understand and evaluate the efficiency of pollinator attachment to a variety of petal surfaces. Although the petal surface texture influenced the attachment, coevolutionary relationships or adaptations between flower surfaces and pollinator tarsi could not be confirmed. Since pollinators appear to be opportunistic, they are expected to attach to a variety of flower surfaces. Rougher surfaces, including conical and papillate epidermal cells, significantly increased the foothold of flies and honeybees, while flat, tabular epidermal cells covered with microstructures like cuticular folds and epicuticular wax crystals impaired attachment. Carniolan honeybees generated larger forces than greenbottle flies, but the latter showed higher safety factors. However, tendencies in attachment ability toward sufficient and insufficient substrates are similar in flies and bees.

How tight are beetle hugs? Attachment in mating leaf beetles

Similar to other leaf beetles, rosemary beetles Chrysolina americana exhibit a distinct sexual dimorphism in tarsal attachment setae. Setal discoid terminals occur only in males, and they have been previously associated with a long-term attachment to the females back (elytra) during copulation and mate guarding. For the first time, we studied living males and females holding to females elytra. Pull-off force measurements with a custom-made tribometer featuring a self-aligning sample holder confirmed stronger attachment to female elytra compared with glass in both males and females; corresponding to 45 and 30 times the body weight, respectively. In line with previous studies, males generated significantly higher forces than females on convex elytra and flat glass, 1.2 times and 6.8 times, respectively. Convex substrates like elytra seem to improve the attachment ability of rosemary beetles, because they can hold more strongly due to favourable shear angles of legs, tarsi and adhesive setae. A self-aligning sample holder is found to be suitable for running force measurement tests with living biological samples.

Plant pressure sensitive adhesives: similar chemical properties in distantly related plant lineages.

AbstractMain conclusionA mixture of resins based on aliphatic esters and carboxylic acids occurs in distantly related generaPeperomiaandRoridula, serving different functions as adhesion in seed dispersal and prey capture. According to mechanical characteristics, adhesive secretions on both leaves of the carnivorous flypaper Roridula gorgonias and epizoochorous fruits of Peperomia polystachya were expected to be similar. The chemical analysis of these adhesives turned out to be challenging because of the limited available mass for analysis. Size exclusion chromatography and Fourier transform infrared spectroscopy were suitable methods for the identification of a mixture of compounds, most appropriately containing natural resins based on aliphatic esters and carboxylic acids. The IR spectra of the Peperomia and Roridula adhesive resemble each other; they correspond to that of a synthetic ethylene–vinyl acetate copolymer, but slightly differ from that of natural tree resins. Thus, the pressure sensitive adhesive properties of the plant adhesives are chemically proved. Such adhesives seem to appear independently in distantly related plant lineages, habitats, life forms, as well as plant organs, and serve different functions such as prey capture in Roridula and fruit dispersal in Peperomia. However, more detailed chemical analyses still remain challenging because of the small available volume of plant adhesive.

New results on sexual differences in tarsal adhesive setae of Diabrotica virgifera virgifera LeConte (Coleoptera, Chrysomelidae, Galerucinae)

Previous light microscopy studies revealed a hairless patch on the feet of male Diabrotica virgifera virgifera. However, in related species of chrysomelid beetles the males have special adhesive setae with discoid terminals, which adhere to the elytra of females during copulation. In the present study, we examined the pretarsi of D. virgifera virgifera at a high magnification using scanning electron microscopy. The distinct sexual tarsal dimorphism in this species is confirmed. However, our results do not support the presence of a hairless patch on the feet of males, but a field of densely-packed male-specific adhesive setae with discoid terminals.

Attachment ability of the southern green stink bug, Nezara viridula (L.), on plant surfaces

Traction forces of male and female southern green stink bugs Nezara viridula (L.) were measured on adaxial leaves of green beans (Phaseolus vulgaris L. cv. ‘Nagauzura’), peas (Pisum sativum L. cv. ‘Hakuryu’), rice (Oryza sativa L. cv. ‘Mac hin sung’), and soybean (Glycine max [L.] Merr. cv. ‘Enrei’), as well as on glass as a control surface. Bugs attached well on three-dimensionally structured surfaces covered with anti-adhesive epicuticular wax crystals. Strongest pulls were generated on adaxial green bean leaves, corresponding to safety factors (traction force/body weight) of 11.1 and 11.6 in males and females, respectively. These values were slightly lower on soybean (males: 7.4, females: 8.0) and rice leaves (males: 8.9, females: 10.6). Trichomes and papillae are assumed to promote pentatomid bug’s attachment. On tabular, wax-covered pea leaves, safety factors decreased significantly to 1.7 and 1.6, in males and females, respectively. Differently, on non-structured glass, safety factors resembled those on rice and soybean leaves (males: 9.6, females: 8.0). No statistical differences in traction force and safety factor between sexes were detected on any substrate. Surface wettability did not significantly affect the results. Both robust claws and tough adhesive pads enable the N. viridula bugs to grasp and adhere to a wide range of various plant substrates, including such ones covered with anti-adhesive wax crystals. However, tabular, pruinose pea leaves were detected to prevent the foothold of the southern green stink bugs, although pea is known as one of their common host plants.