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Photo#310002
Caterpillar with a problem - Eulophus

Caterpillar with a problem - Eulophus
Elkton, Douglas County, Oregon, USA
July 25, 2009
Size: approx 23mm
Very odd. I returned the following day, and the caterpillar was gone, however, all the little larva, which I thought were parasitic, remained behind.

Anyone know what's going on here?

I'd put them in a jar to see what they turn into, but I have no idea what to feed them.

Images of this individual: tag all
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Moved
Moved from parasitic Apocrita.

Moved
Moved from Cocoons and larvae.

By the way, Eulophids are Chalcids
not Ichneumonids. We may want to have someone check the placement of these images. Wish we knew more.

What's Going On Here:
The larvae are probably ichneumonoid wasps- most of the ones I've seen identified here turn out to be Braconids. The larvae live inside the caterpillar until they're about ready to pupate, at which time they eat their way out, fatally wounding the host in the process.
My best guess is that they ate the caterpillar until it was almost dead, then emerged. The caterpillar probably either crawled away, was eaten, or dropped off the leaf. The larvae no doubt massed together for protection.
These are parasitoids, so they probably wouldn't eat anything but internal tissues of a live caterpillar. I'm sure they'll pupate soon.

 
Good explanation
However some parasitoids live outside of their hosts, rather than inside, ectoparasitoids. This is the case here and in a few others.

See Bulletin of Entomological Research

 
ectoparasitoids
Looking at this caterpillar, with the row of larva being somewhat neatly placed on only one side, it makes sense that these might have been living outside the host. It even appears the eggs might have been placed in the folds of the abdominal segments. If they were internal, I would think they'd emerge more randomly, and perhaps the caterpillar would look more "wounded". Also, I'd now think that the caterpillar would have been in a much sorrier state if that many larva of that size were feeding within it - the caterpillar actually still looks quite healthy and robust for being the caretaker of such a large brood. (Can I assume that not all parasites deplete, to the death, their hosts?)

 
Maybe
But I doubt it, my caterpillar (above) seemed very healthy with 8 parasitoids hanging from it; two days later, at 8:20 AM it looked like the image above and by 5 PM it was like this:
So it went from a green necklace to suckling piglets to lions devouring a zebra. (Video)
As far as I know the members of the subfamily Eulophinae are ectoparasitoids.

 
Also a very interesting video.
Had I known this could have been the fate of the caterpillar, I'd have kidnapped the whole group and documented the caterpillar's final participation,too. Next time!

 
Parasites vs. parasitoids
Parasitoids, by definition, typically kill their hosts, whereas parasites typically do not. However, many braconid larvae leave their host fairly intact and alive-ish for a while after they have exited its body. See the 2nd and 4th videos here for examples.

Offhand, I can't think of any examples of truly parasitic wasps, but there probably are some.

 
Very interesting videos.
If I find another of these events, I'll kidnap the whole group, including the caterpillar, right away. I did look for this caterpillar when I collected the larva, but I couldn't find it on or under the tree.

 
Thanks Chuck,
Sounds like I probably won't kill anything by trying to raise them in a safe jar. Any idea how long it takes to turn into a wasp?

:-P)

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