Stiffness gradients facilitate ovipositor bending and spatial probing control in a parasitic wasp

Many parasitic wasps use slender and steerable ovipositors to lay eggs in hosts hidden in substrates, but it is currently unknown how steering is achieved. The ovipositors generally consist of three longitudinally connected elements, one dorsal and two ventral valves that can slide along each other. For the parasitic wasp Diachasmimorpha longicaudata, it has been shown that protraction of the ventral valves causes incurving of the ventral valves towards the dorsal one, which results in a change in probing direction. We hypothesize that this shape change is due to differences in bending stiffness along the ovipositor. Alignment of the stiff tip of the dorsal valve with a more flexible ventral S-shaped region situated just behind the tip straightens this S-bend and results in upwards rotation of the ventral tip. We show that the S-shaped region of the ventral valves has a low bending stiffness because it contains soft materials such as resilin. In contrast, the large cross-sectional area ...