Quantification of Bush-Cricket Acoustic Trachea Mechanics Using AFM Nanoindentation

Derived from the respiratory tracheae, bush-crickets’ acoustic tracheae (or ear canal) are hollow tubes evolved to transmit sounds from the external environment to the interior ear. Due to the location of the ears in the forelegs, the acoustic trachea serves as a structural element that can withstand large stresses during locomotion. Despite this unique functional adaptation, its mechanical properties have received insufficient investigation. Chitinous taenidia are the main rigidity components of acoustic trachea and the primary contributor to its mechanical stiffness. In this study, we report a new Atomic Force Microscopy Force Spectroscopy (AFM-FS) approach to quantify the mechanics of taenidia in the bush-cricket Mecopoda elongate. Mechanical properties were examined over the longitudinal axis of hydrated taenidia by indenting single fibres in the nanoscale range using precision hyperbolic tips. Analysis of the force-displacement (F-d) extension curves at low strains using the Hertzian contact model showed Elastic modulus distribution between 13.9MPa to 26.5GPa. AFM topography imaging showed the surface configuration and curvature of taenidia fibres. Finite-element analysis was conducted in support of the experimental set-up using a linear elastic model for shallow indentation depths. Variation of modulus indicates a complex mechanical behaviour of taenidia due to an intricate chitin-resilin composition and strongly suggests that elasticity is a key parameter for optimization in the evolutionary process.