This Week's Sci-Fi Worthy Parasite: Cotesia glomerata

Parasitic wasps are always an easy target as sci-fi parasites. After all, they were the main inspiration behind the film "Alien" - clearly they're 'sci-fi worthy'. They all do terrible, mean things to their hosts while they eat them alive from the inside out. And, simply, they're just really, really awesome parasites.

This week's wasp, however, is even more special: it's about to be featured in an upcoming National Geographic Channel event called In The Womb: Extreme Animals. Don't worry - I'll give you the down and dirty details on that soon (it premiers on May 10th, just for a head's up). In the meantime, you get to see really awesome images (and video!) of this week's lovely parasitic wasp from the upcoming show.

These parasitic wasps are actually invasive, having been brought to North America in 1883 as a form of biocontrol of the cabbageworm which was an agricultural pest at the time. Soon after, they were introduced all over the world. Like almost all biocontrol efforts, the introduction of these parasitic wasps has had side effects on native species. Empirical studies suggest that Cotesia glomerata is at least partially, if not wholly responsible for the collapse of mustard white butterfly (Pieris napi) populations in Massachusetts 1. In the Canary Islands, the wasps have been singled out as a major threat to native butterfly populations by DNA evidence 2.

Cotesia glomerata (also called Apanteles glomerata), like many other parasitic wasps, targets catterpillars to host its hungry little wasps-to-be. When it finds a suitable host, it injects its eggs directly into the body cavity of the unfortunate butterfly larvae by stabbing its egg-laying, needle-like appendage called an "ovipositor" directly through the catterpillar's skin. Inside the host, the eggs hatch and begin feeding on the inner organs to become fully grown.

Cotesia glomerata larvae inside a caterpillarWhat's fascinating about Cotesia glomerata (and its closest relatives) is that to protect their young from the catterpillar's immune system, they coat the eggs in a virus which disables the caterpillar's immune system and chemically castrates the unlucky bug. The DNA for the virus particles are integrated into the wasps genome, which, scientifically speaking, is an incredible evolutionary adaptation. We only recently discovered that the genetic material to create these protective viruses came from a viral infection in the wasp over 100 million years ago 3. Without the virus to protect them, the larvae would be attacked by the catterpillar's internal defenses and die.

The larvae, which eat the catterpillar from the inside out, target the organs in such an order that the catterpillar lives as long as possible. Once they've had their fill, they exit the catterpillar and pupate, forming their cocoons so they transform into adult wasps. But the poor little catterpillar's job isn't over yet. Before it dies, it spins a web of silk to protect the little babies that just ate its internal organs, and acts like a bodyguard, vehemently defending the metamorphosizing wasps until they emerge. Only then does it get the sweet release of death. Here's a clip from the upcoming Nat Geo special detailing the emergence of the young wasps:

C'mon. Tell me that's not one of the coolest things you've ever seen.

Well, I don't believe you. It's frickin' awesome! Parasites just rock, don't you think? "Degenerates" my butt...

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The wasp pupae need an active defense from what exactly? Predators - or other parasites?