Originally published October 31, 2020.
Nature’s most gruesome can rival a horror movie. A perfect example is the ominous way the Emerald Jewel Parasitoid Wasp turns the American cockroach into a zombie, kidnaps it, and precisely lays its eggs on the roach. The wasp larvae then develop on and in this living nursery, consuming it slowly as they grow.
From the start, it seems an unlikely interaction. The cockroach is much bigger than the wasp. “This has led to the evolution of some really remarkable tricks of the trade for the wasp”, Ken Catania told Quirks & Quarks host Bob McDonald. Catania, a biologist at Vanderbilt University in Nashville, Tennessee, just published a new study in which he showed how the wasp uses a series of precisely targeted stings to gain control of the cockroach.
Precision bites make a good zombie
The first puncture targets the first thoracic ganglion, part of the central nervous system. This paralyzes the cockroach’s front legs. This is followed shortly after by a second, well-directed bite into the cockroach’s brain. The stings are not meant to kill, but to give the wasp control.
“He can’t just cripple the cockroach and drag it into a hole,” Catania said. “So he instead made the cockroach into a zombie so he could lead it into a hole, lay an egg on the cockroach, barricade it, and then nasty things happen from there.”
The first part of this interaction was already known to biologists. Catania’s new idea is that the wasp’s manipulation of its victim doesn’t stop there. He discovered that the wasp stings the cockroach three more times while it is laying its eggs.
The wasp must place its egg in a precise position on the cockroach’s body, called the coxal plate, or the larvae will die. This target on the body can sometimes be blocked by the roach’s long, articulated legs.
“The wasp has this last challenge,” Catania said. “The cockroach’s legs may be in the wrong position, so the solution is to go back into the nervous system and bite straight into a new place. And that new place is in the area that controls the cockroach’s second legs, and that makes that the leg essentially extends and that allows the last stage of the laying. “
A blood meal, a cocoon and an alien-style birth
With the hip plate now exposed, the wasp lays its egg and the larvae begin to develop and become hungry.
“This is where it gets even more gruesome,” Catania said. “After that [the larvae] takes a blood meal for a few days outside the cockroach, it burrows inside the cockroach, eats the cockroach alive from the inside, forms a cocoon, and then eventually comes out of the cockroach alien style. “
It turns out that the wasp itself is something of a zombie, Catania discovered, in that it is locked into a biologically programmed behavior that it cannot escape.
He was curious what would happen if the set of three poisonous bites did not work and the cockroach’s legs remained without extension, blocking the critical location for egg placement.
He stuck the paws in place on the cockroach and then observed how the wasp reacted. What he saw made him jump. Like a frustrated robot, the wasp continued to sting the critical location, sometimes over 100 times, in an attempt to straighten the leg.
Catania said he couldn’t help but be impressed by the wasp’s high precision in behavior.
“This wasp evolved to essentially find the central nervous system, find the brain, and precisely deliver venom to affect the cockroach’s behavior in the right way without killing it.
“It’s not quite like the lunch scene on the Nostromo of [the movie] Extraterrestrial, but it’s as close as you can imagine to the organic world. So it’s straight out of science fiction. “
Written and produced by Mark Crawley