Mandible composition and properties in two selected praying mantises (Insecta, Mantodea)

Insects process their food with their cuticle-based mouthparts. These feeding structures reflect their diversity and can, in some cases, showcase adaptations in material composition, mechanical properties, and shape to suit their specific dietary preferences. To pave the way to deeply understand the interaction between mouthparts and food and to determine potential adaptations of the structures to the food, this study focuses on the mandibles of two praying mantis species. Gongylus gongylodes feeds mainly on Diptera, and Sphodromantis lineola forages on larger prey. Employing scanning electron microscopy, the mandibular morphologies were analyzed. The degree of the cuticle tanning was tested using confocal laser scanning microscopy. Furthermore, the contents of transition and alkaline earth metals in the mandible cuticle were studied using energy-dispersive X-ray spectroscopy and the mechanical properties tested by nanoindentation. We found that S. lineola mandibles show pronounced gradients of Young's modulus and hardness from the basis to the tip, which might be an adaptation against high stresses during biting and chewing. G. gongylodes, in contrast, did not show pronounced gradients, which may indicate that there is less stress involved in feeding-necessary to test in future studies. The mechanical properties of manidibles in both species are related to the degree of cuticle tanning but also positively correlate with the content of magnesium. These findings enrich our understanding of insect cuticle biology but also present new sets of data on praying mantis structures.