A dermal light sensor controls anisotropic biomechanical properties in insect cuticle

The cuticle of many insects shows the presence daily growth bands, consisting of alternating layers of parallel chitin fibres deposited during the day and helicoidal fibres deposited at night. In locusts this rhythmic deposition is controlled by a circadian mechanism linked to a local epidermal light sensor. So far, it is not understood if this light sensitivity leads to any biomechanical advantages. It is here hypothesized that the light sensor may act as an external trigger, using consistent environmental stimuli to regulate the fibre deposition process. This regulation could serve to override the self-organized helicoidal arrangement and prevent the accumulation of irregularities at the cellular level during cuticle formation. Based on established principles of fibre-reinforced composite materials, the presence of regular cuticular growth bands likely influences the biomechanical properties of the cuticle, particularly its anisotropic response to mechanical stresses such as tension and compression. This study employs a combined approach of simulated chitin-fibre deposition and standardized finite element modeling to demonstrate that an external trigger can play an important role in controlling the anisotropic biomechanical properties of insect cuticle.