Oviposition digging in the grasshopper. I. Functional anatomy and the motor programme.

The ovipositor appendages of acridid insects (grasshoppers and locusts) consist of two pairs of shovel-shaped valves that are used to dig a deep chamber in the ground for egg burial, to manipulate the eggs, and to assist in capping the egg-pod with froth. During oviposition the valves undergo cyclical opening, closing, retraction and protraction movements. These movements are produced by the contractions of ten pairs of muscles. The eighth and ninth segmental nerves of the terminal abdominal ganglion supply the ovipositor muscles. Rhythmical ovipositor movements are produced by the severed abdomen of sexually mature female grasshoppers. By comparing this activity to the activity underlying the natural behaviour, it was determined that the isolated abdomen produced the digging portion of the oviposition motor programme. Electrical recordings from the ovipositor nerves in the isolated nervous system showed spontaneous rhythmical bursting activity. This activity corresponds to the neural correlate of digging behaviour and indicates the presence of a central pattern generator for oviposition digging in the terminal abdominal ganglion of females.