Unlike other venomous predators, the parasitoid wasp Ampulex compressa incapacitates its prey, the cockroach Periplaneta americana, to provide a fresh food supply for its offspring. We first established that the wasp larval development, from egg laying to pupation, lasts about 8 days during which the cockroach must remain alive but immobile. To this end, the wasp injects a cocktail of neurotoxins to manipulate the behavior of the cockroach. The cocktail is injected directly into the head ganglia using biosensors located on the stinger. The head sting induces first 30 min of intense grooming followed by hypokinesia during which the cockroach is unable to generate an escape response. In addition, stung cockroaches survive longer, lose less water, and consume less oxygen. Dopamine contained in the venom appears to be responsible for inducing grooming behavior. For the hypokinesia, our hypothesis is that the injected venom affects neurons located in the head ganglia, which send descending tonic input to bioaminergic neurons. These, in turn, control the thoracic premotor circuitry for locomotion. We show that the activity of identified octopaminergic neurons from the thoracic ganglia is altered in stung animals. The alteration in the octopaminergic neurons' activity could be one of the mechanisms by which the venom modulates the escape circuit in the cockroach's central nervous system and metabolism in the peripheral system.
Copyright 2005 Wiley-Liss, Inc.