The parasitoid wasp Ampulex compressa hunts cockroaches Periplaneta america
na, stinging them first in the thorax and then in the head, the sting penet
rating towards the subesophageal ganglion. After being stung the cockroach
grooms almost continuously for approximately 30 min, performing all the nor
mal components of grooming behavior. This excessive grooming is only seen a
fter the head sting and cannot be attributed to stress, to contamination of
the body surface or to systemic or peripheral effects. This suggests that
the venom is activating a neural network for grooming.
We suggest that the venom induces prolonged grooming by stimulating dopamin
e receptors in the cockroach, for the following reasons. (1) Reserpine, whi
ch causes massive release of monoamines, induces excessive grooming. (2) Do
pamine injected into the hemocoel also induces excessive grooming and is si
gnificantly more effective than octopamine or serotonin. In addition, the d
opamine agonist SKF 82958 induces excessive grooming when injected directly
into the subesophageal ganglion. (3) Injection of the dopamine antagonist
flupenthixol greatly reduces venom-induced grooming. (4) Dopamine, or a dop
amine-like substance, is present in the venom.