Ampulex compressa, or jewel wasp, is a solitary parasitoid which uses cockroaches as the host for its larva. Its particular method of reproduction is astounding, using the specific administration of neurotoxins first to the thoroidal ganglia of a roach to induce a temporary paralysis, then to the subesophageal ganglion, completely disabling its escape reflex. The wasp's stinger is thought to be directed towards this specific region of the roach's brain by extremely sensitive detectors along the stinger. The effect is permanent, unlike the effect of the same poison injected into the roach's motor neurons.

Normal cockroaches are amazing evaders of potential predators, running 70-80 cm/s while changing direction based on shifting air currents over its anal cerci, but the placid state the cockroach enters after the second sting leaves it so open to suggestion that the wasp can actually hold onto its antennae and ride it, directing its movement into a burrow. The wasp is too small to be able to carry a paralyzed cockroach without the roach's help.

Once the hapless roach is situated in the burrow, the wasp proceeds to lay an egg on its belly. The wasp leaves the cockroach, which is completely immobile without the wasp's direction, and fills in the end of the burrow with pebbles. It then leaves to resume its normal life.

The roach remains docile while the egg hatches, and the larvae behaves as the larvae of other parasitoid wasps, entering through the abdomen of the cockroach. It eats the internal organs in an order that keeps the cockroach alive for the duration of the gestation period. The larvae then weaves a cocoon within the cockroach's abdomen, eventually emerging from the cockroach as a fully developed wasp.

The venom the wasp uses to produce this amazing change in cockroach behavior has not been identified by any known catalyst, due to the evolution of the toxin to the specific purpose of deactivating roach brains.

This is the first fully documented case of a parasitoid injecting venom directly into a host's brain, though there are other species suspected of using similar methods, such as Liris nigra's relationship with crickets.

sources: Direct Injection of Venom by a Predatory Wasp into Cockroach Brain -Gal Haspel Escape Behavior in the American Cockroach-Joseph Sullivan The venom of Ampulex compressa--effects on behaviour and synaptic transmission of cockroaches. (Piek T. et all)

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