Evaporation dynamics of tarsal liquid footprints in flies (Calliphora vicina)and beetles (Coccinella septempunctata)

Abstract

SUMMARYInsect tarsal adhesive structures secrete a thin layer of fluid into the contact area. It was previously reported that the presence of this fluid significantly increases adhesion on various substrata. Previous data obtained from representatives of different insect groups suggest a difference not only in the chemical composition of the fluid, but also in its physical properties. In the present study, we have measured for the first time changes in the droplet geometry over time and the evaporation rate of the fluid in flies (Calliphora vicina) and beetles (Coccinella septempunctata) by the use of atomic force microscopy. Flattened droplets of the beetle had lower evaporation rates than hemispherical footprints of the fly. Within 1h, the droplet volume reduced to 21% of the initial volume for the fly, and to 65% for the beetle, suggesting a larger fraction of volatile compounds in the fly fluid. It was revealed that drop geometry changes significantly during evaporation and shows pinning effects for the fly footprints due to an assumed self-organizing oil layer on top of the water fraction of the micro-emulsion. The data obtained suggest that the adhesion strength in capillarity-based switchable adhesive systems must be time-dependent because of the specific evaporation rate of the adhesive fluid. These results are important for our understanding of the functional mechanism of insect adhesive systems and also for biomimetics of artificial capillarity-based adhesive systems.

Comparative study of the fluid viscosity in tarsal hairy attachment systems of flies and beetles

“…It was found that the secretion in hairy attachment pads of beetles is mainly lipidbased [25][26][27] with a small water fraction, whereas in flies it is assumed to be a mainly water-based microemulsion [6] with low lipid content. These data were recently supported by measuring the evaporation dynamics of the tarsal secretions in beetles and flies [28].…”

“…In [34], collection duration for a sufficient amount of liquid was about 4 -5 h. In this study, we refined our preparation technique to allow for a faster collection (within 1 h). A longer collection time may have led to more evaporation of the liquid especially of its volatile fractions [28], and therefore an effect of evaporation time on viscosity cannot be excluded. Indeed, the varying amount of volatile components in the secretion of the beetle and the fly was already shown to result in different evaporation rates [28].…”

“…A longer collection time may have led to more evaporation of the liquid especially of its volatile fractions [28], and therefore an effect of evaporation time on viscosity cannot be excluded. Indeed, the varying amount of volatile components in the secretion of the beetle and the fly was already shown to result in different evaporation rates [28]. Within 1 h, the secretion volume reduced to 21% of the initial volume for the fly, and to 65% for the beetle suggesting a larger fraction of volatile compounds in the fly fluid.…”

Evidence for a material gradient in the adhesive tarsal setae of the ladybird beetle Coccinella septempunctata

“…Based on our assumption that the presence of high resilin concentrations in the setal tips increases the attachment ability of the adhesive pads, it becomes obvious that the hydration of resilin may be essential for keeping the attachment performance of the beetles on a high level. In this context, it is imaginable that the beetles' tarsal liquids, which evaporate relatively slowly 42 , have the function to cover the setae and thereby maintain the hydration of the resilin in the setal tips.…”

Contact solid-phase microextraction with uncoated glass and polydimethylsiloxane-coated fibers versus solvent sampling for the determination of hydrocarbons in adhesion secretions of Madagascar hissing cockroaches Gromphadorrhina portentosa (Blattodea) by gas chromatography-mass spectrometry

“…The non-polar fraction of these components probably largely contributes to the waterproofing function of the lipid layer of the outer cuticle such as that of the tibia. In the tarsal adhesive, the hydrophobic phase of the postulated emulsion or suspension probably prevents its aqueous phase from premature desiccation [6,42].…”