Neuromodulation of the escape behavior of the cockroach Periplaneta americana by the venom of the parasitic wasp Ampulex compressa

Abstract

• 1. The wasp Ampulex compressa hunts cockroaches as food for her offspring. Stung cockroaches show little spontaneous movement although they are able to move. Wind stimuli to the cerci, which normally produce escape responses, are no longer effective in stung cockroaches. In the present paper, we have searched for neural correlates responsible for the impairment of the escape behavior by the venom.

• 2. In control cockroaches, a typical motor response in the coxal depressor muscle to wind or tactile stimuli consists of an initial burst of the fast and slow depressor motoneurons followed by rhythmic discharges. In stung cockroaches, both stimuli evoke only a burst in the slow but no discharge activity in the fast depressor neuron. Intracellular recordings from the fast depressor motoneuron in stung cockroaches demonstrate that it still receives synaptic input, though subthreshold, from thoracic interneurons associated with the wind mediated escape circuitry. Discharge activity of the slow motoneuron lacks the rhythmic bursting pattern characteristic for slow walking in control animals.

• 3. Yet, the venom affects neither the response of descending mechanosensitive giant interneurons to tactile stimuli nor the response of the abdominal giant interneurons to wind stimuli, both of which are known to excite the thoracic interneurons. The venom has also no effect on neuromuscular signal transmission.