for National Geographic News
The parasitic jewel wasp uses a venom injected directly into a cockroach's brain to inhibit its victim's free will, scientists have discovered.
The venom blocks a chemical substance called octopamine in the cockroach's brain that controls its motivation to walk, the study found.
Unable to fight back, the "zombie" cockroach can be pulled into the wasp's underground lair, where an egg is laid in its abdomen. The larva later hatches and eats the still living but incapacitated cockroach from the inside out.
"The whole thing takes about seven to eight days, during which the meat has to be fresh," said study co-author and neurobiologist Frederic Libersat of Ben-Gurion University of the Negev in Be'ér Sheva, Israel.
"If you kill a cockroach, it rots within a day."
The mature wasp emerges from the bug victim's body after about a month.
The study recently appeared in the Journal of Experimental Biology.
The team of researchers at Ben-Gurion University believe that the octopamine discovery is an important piece of the puzzle of how the tropical wasp's venom turns its victims into the living dead.
Octopamine is a brain substance that places insects in an alert state, inspires them to move, and allows them to perform demanding physical tasks.
"It serves the same functions as noradrenaline, which is involved in the fight-or-flight reaction ... in the vertebrate brain," Libersat said.
The team determined that the wasp injects its venom into a specific area of the cockroach's brain, the protocerebrum.
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