Morphological and biomechanical adaptations of larval mandibles in Trichoptera (Insecta)

Abstract This study examines the larval mandibles of five caddisfly species, documenting their morphological and biomechanical adaptations to different feeding strategies. Three predatory species ( Molanna angustata , Plectrocnemia conspersa , Rhyacophila fasciata ) and two algae‐grazing species ( Silo nigricornis , Tinodes pallidulus ) were investigated using scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), confocal laser scanning microscopy (CLSM) and nanoindentation. SEM analysis revealed distinct mandible structures: grazing species possessed various collecting setae and sharp mandible cutting edges, while predatory species exhibited more pointy incisors. By EDX, low concentrations of Ca, Cl, Cu, Fe, K, Mg, Mn, P, S, Si and Zn were detected with no relationship to mechanical properties, suggesting limited elemental reinforcement in larval Trichoptera mandibles. CLSM imaging, however, revealed regional material heterogeneities related to the mechanical properties, indicating that the mechanical parameters depend on the degree of cuticle tanning. We detected harder and stiffer mandible cuticle in predatory species, likely enhancing the mechanical resistance of material during prey capture. Nanoindentation analysis identified two functional mandible types in grazers, adapted for scraping and collecting, with differential regional cuticle hardness and stiffness. Predatory species exhibited three mandible types, likely specialized for grabbing and crushing, piercing and cutting, or grabbing, piercing and cutting. Decreased mechanical properties of condyles in predators suggested enhanced flexibility for prey handling, whereas grazers, showing higher Young's moduli and hardness values in condyles, likely required higher pressure for scraping. In some species ( Silo nigricornis and Rhyacophila fasciata ), the heterogeneity between lateral and medial mandible cuticle indicated that self‐sharpening mechanisms could be present. These findings provide insight into the functional morphology and material adaptations of mandibles of trichopteran larvae in relation to their feeding ecology.