Scale effects on the attachment pads and friction forces in syrphid flies

To test the role of constructional and dimensional factors in the generatio n of friction force by systems of setose attachment pads, sis species of sy rphid fly (Platycheirus angustatus, Sphaerophoria scripfa, Episyrphus balte atus, Eristalis tenax, Myathropa florea and Volucella pellucens) were studi ed using light and scanning electron microscopy. Flies were selected accord ing to their various body mass and attachment pad dimensions. Such variable s as pad area, setal density, the area of a single setal tip and body mass were individually; measured, if, centrifugal force tester, equipped with a fibre-optic sensor, was used to measure the friction forces of the pads on a smooth horizontal surface made of polyvinylchloride. Friction force, whic h is the resistance force of the insect mass against the sum of centrifugal and tangential forces, was greater in heavier insects such as Er, tenax, M . florea and V. pellucens. Although lighter species generated lower frictio nal forces, the acceleration required to detach an insect was greater in sm aller species. The area of attachment pads, setal tip area and setal densit y differed significantly in the species studied, and the dependence of thes e variables on body mass was significant. The frictional properties of the material of the setal tips were not depend ent on the dimensions of the fly species. Similar results were obtained for the frictional properties of the pulvillus as a whole. Thus, the propertie s of the secretion and the mechanical properties of the material of the set al tips are approximately constant among the species studied. It is conclud ed that differences in friction force must be related mainly to variations in the real contact area generated by the pad on the smooth surface. The re al contact area can be estimated as the summed area of the broadened setal tips of the pad in contact with the surface; The real contact area depends on such morphological variables as setal density and the area of a single s etal tip, Although individual variables vary among flies with different dim ensions, they usually compensate such that smaller setal tip area is partia lly compensated for by higher setal density.