A parasitoid wasp manipulates the drive for walking of its cockroach prey

The parasitoid wasp A. compressa hunts cockroaches as a live food supply for its offspring. The wasp selectively injects venom into the cerebral ganglia of the prey to induce long-term hypokinesia [1-5], during which the stung cockroach, although not paralyzed, does not initiate spontaneous walking and fails to escape aversive stimuli. This allows the wasp to grab the cockroach by the antenna and walk it to a nest much like a dog on a leash. There, the wasp lays an egg on the prey, seals the nest, and leaves. The stung cockroach, however, does not fight to escape its tomb but rather awaits its fate, being consumed alive by the hatching larva over several days. We investigated whether the venom-induced hypokinesia is a result of an overall decrease in arousal or, alternatively, a specific decrease in the drive to initiate or maintain walking. We found that the venom specifically affects both the threshold for the initiation and the maintenance of walking-related behaviors. Nevertheless, the walking pattern generator itself appears, to be intact. We thus report that the venom, rather than decreasing overall arousal, manipulates neuronal centers within the cerebral ganglia that are specifically involved in the initiation and maintenance of walking.