This was one class I was not dozing through.

In virology class today we took a break from our usual round of vertebrate viruses, and delved into insect territory. As is often the case, the bugs are for more interesting, just plain bizarre, and in this case...alien-baby-genetic-engineering creepy.

There are two genera (Ichneumid and Brachonid) of wasps that are parasitoids; that is, they lay their eggs in caterpillars, and the eggs hatch and grow inside caterpillars. Except, a healthy caterpillar can reject the egg, and go on about it's business of munching plants and becoming a moth or butterfly. So the wasp injects something that looks like a virus, along with it's egg, and that infects caterpillar cells (but does *not* replicate there), and suppresses the caterpillar immune system so it doesn't reject the wasp egg. These "virus-like particles" confused folk for a long time, because what they've got inside them isn't virus DNA at all; it's *wasp* DNA. Several ring-shaped loops of it (hence the name polydnavirus; virologists are not an imaginative lot when it comes to names). So how do wasps get to make viruses that genetically-engineer caterpillars to incubate their eggs? Because that's essentially what's happening here.

They captured a wild virus; a nudivirus, it turns out, which is now completely integrated into the wasp genome (and by 'captured,' I mean an ancestor-wasp was infected, but instead of making it sick the virus slipped into its genome and was latent, and passed onto it't offspring. Lots of viruses do that). In this case, though, it's only partly latent, and so well regulated that it's *only* expressed during a specific time, in the wasp's ovaries. All the viral replication genes are under wasp control, and used to make viral particles that contain, instead of the viral genome (like you'd expect to find inside a virus), wasp genes that help out it's offspring when they're expressed in the caterpillar.

It reminds me of mitochondria, which are similarly symbiotic, but *ever* so much more creepy. I *love* it.