'Easy bleeding' bearing relations to special cuticle structures in sawfly larvae (Hymenoptera: Tenthredinidae)

Spindler Barth, M.; Burret, M.; Spindler, K. D. eter

Larvae from several insect species secrete hemolymph, which contains deterrent compounds, as chemical defence strategy against predators. The cuticle of some Tenthredinidae (Hymenoptera, Symphyta) is ruptured very easily after a mild mechanical stress. The cuticle structure of larvae capable of 'easy wounding' was compared with some related species with reduced or no capacity for 'easy wounding'. Larvae of several Blennocampinae, the most efficient 'easy bleeders' have a highly sculptured cuticle, which is associated with pronounced differences in cuticle thickness. A hexagonal pattern, which corresponds to the thinner parts of the cuticle is stained with a N-acetylgalactosamine specific antibody. No exo- and endocuticle can be discriminated in non-lamellate cuticle. Chitin fibres form a loose 3D network. According to electron probe microanalysis Ca2+ is present. In contrast, in cuticle of larvae with a high mechanical resistance multiple lamellae are visible, but no hexagonal pattern can be stained with the same antibody. Ca2+ is absent. Larvae from species with minor capacity for 'easy bleeding' show an intermediate cuticular structure. The impact of cuticle structure on mechanical resistance is discussed.