Wasp Voodoo Rituals, Venom-Cocktails, and the Zombification of Cockroach Hosts

Abstract

The parasitoid Jewel Wasp uses cockroaches as a live food supply for its developing larvae. The adult wasp uses mechanoreceptors on its stinger to locate the host's cerebral ganglia and injects venom directly into the cockroach's "brain," namely in the subesophageal ganglion and in and around the central complex in the supraesophageal ganglion. As a result, the cockroach first engages in continuous grooming for roughly 30 min. Dopamine identified in the wasp's venom is likely to cause this grooming, as injecting a dopamine-receptor antagonist into the cockroach hemolymph prior to a wasp's sting greatly reduced the venom-induced, excessive grooming. Conversely, injecting a dopamine-receptor agonist into the brain induces excessive grooming in normal cockroaches. A second effect of the head-sting is the induction of a long-lasting lethargic state, during which the cockroach demonstrates a dramatically reduced drive to self-initiate locomotion. Unlike most paralyzing venoms, Ampulex's venom seems to affect the "motivation" of its host to initiate locomotion, rather than affecting the motor centers directly. In fact, the venom specifically increases thresholds for the initiation of walking-related behaviors and, once such behaviors are initiated, affects their maintenance without affecting the walking-pattern generators. Thus, the venom manipulates neuronal centers within the cerebral ganglia that are specifically involved in the initiation and maintenance of walking. We have shown that in stung cockroaches focal injection of an octopaminergic receptor agonist around the central complex area in the brain partially restores walking. Another likely candidate target of the venom is the opioid system, which is known to affect responsiveness to stimuli in insects. Opioid receptor agonists increase startle threshold in control cockroaches and using a bioassay for opioid receptors, we found that the venom blocks opioid-like receptors. This effect is reversed with naloxone, an opioid antagonist.