Crystalline wax coverage of the cuticle in easy bleeding sawfly larvae.

The larvae of some sawfly species belonging to the family Tenthredinidae (Hymenoptera) are capable of 'easy bleeding', an anti-predator defence strategy based on a specialised cuticle that can readily break, which frees droplets of distasteful haemolymph. Using high-resolution cryo-scanning electron microscopy, we compared the cuticle surface between easy bleeder (Rhadinoceraea micans, Phymatocera aterrima, Aneugmenus padi) and non-easy bleeder (Strongylogaster multifasciata, Nematus pavidus, Arge pagana) sawfly species. We detected crystalline waxes only on the cuticle surface of easy bleeders. Wax crystals varied in shape and dimension depending on species. We assume the reduction of surface wettability by oozed haemolymph to be the primary function of the wax crystal coverage in the easy bleeding defence strategy.