NEUROMODULATION OF THE ESCAPE BEHAVIOR OF THE COCKROACH PERIPLANETA-AMERICANA BY THE VENOM OF THE PARASITIC WASP AMPULEX COMPRESSA

1. The wasp Ampulex compressa hunts cockroaches as food for her offspr ing. Stung cockroaches show little spontaneous movement although they are able to move. Wind stimuli to the cerci, which normally produce es cape responses, are no longer effective in stung cockroaches. In the p resent paper, we have searched for neural correlates responsible for t he impairment of the escape behavior by the venom. 2. In control cockr oaches, a typical motor response in the coral 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 cockro aches, both stimuli evoke only a burst in the slow but no discharge ac tivity in the fast depressor neuron. Intracellular recordings from the fast depressor motoneuron in stung cockroaches demonstrate that it st ill receives synaptic input, though subthreshold, from thoracic intern eurons associated with the wind mediated escape circuitry. Discharge a ctivity of the slow motoneuron lacks the rhythmic bursting pattern cha racteristic for slow walking in control animals. 3. Yet, the venom aff ects neither the response of descending mechanosensitive giant interne urons to tactile stimuli nor the response of the abdominal giant inter neurons to wind stimuli, both of which are known to excite the thoraci c interneurons. The venom has also no effect on neuromuscular signal t ransmission.