Experimental Analysis of Adhesion of Chrysolina Polita (Chrysomelidae: Coleoptera) on a Variety of Surfaces

Abstract

1. Pulling forces of Chrysolina polita (L.) on glass, perspex and cloth have been recorded and are plotted against body weight. The additional weight of eggs in many of the females is probably the main reason that, in females, pulling forces do. not increase significantly with body weight, whereas those of males do. 2. Pulling forces on glass and perspex are significantly correlated but, in general, neither are significantly correlated with those on cloth. This is because traction on glass and perspex is achieved by the adhesive setae, and on cloth by the tarsal claws. 3. Counts of the adhesive setae in 14 individuals indicate that numbers of climbing setae in females and males and females (combined), male setae in males, and the total number of adhesive setae in males, all show a significant increase with body weight. 4. Pulling force increases with the total number of adhesive setae in females, and males and females (combined). Multiple regression analysis confirms the view that pulling force is a function of the number of adhesive setae. 5. Hooks, suction, electrostatic forces and seizure are largely discredited, and molecular adhesion between the setae and the substratum, and possibly the cohesive forces and surface tension of a thin fluid layer, are confirmed as the most likely modes of adhesion on smooth surfaces in C. polita and most beetles. 6. It is proposed that the main forces of detachment acting on a leaf beetle are probably drag and the whiplash effect of the leaves and branches. Estimates for the wind speeds required to remove beetles from glass and cloth by drag forces alone are calculated.