Polydnaviruses: Nature’s GMOs

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The wasps in the video below are most likely from the family Braconidae. These wasps make their living as parasitoids, growing within other animals and eventually eating them from the inside out. Their life starts as an egg which is laid in the caterpillar by a female. This egg may divide into many, many larvae which feed on the caterpillar from the inside by either eating the caterpillar’s fat body, it’s muscles or by drinking it’s hemolymph (which functions as blood). After they’ve completed their development, they simply exit the caterpillar by burrowing out of it and then pupate. A few weeks later, adult wasps emerge to fly away and look for other hosts.

So what makes Braconid (and Ichneumonid!) wasps so strange, and why am I writing about them on Biofortified?

Well, it turns out that Braconid and Ichneumonid wasps actually modify their hosts genetically by doing something which very much resembles gene therapy.

Most of the time we modify organisms because we want them to do something they currently don’t do. To use the example of BT corn, the corn plant was a better host for the European corn borer than we liked, so we took a protein from a bacteria which was known to kill the larvae which bored into the stalks but also known to be harmless to mammals and made the corn produce the protein which harmed the caterpillar and thus made a relatively bug-proof crop as far as the major pest was concerned.

Well, the caterpillars also produce genes which are bad for the wasps…these genes are involved in the immune system. The immune system’s role is to kill foreign invaders and if you fall under that category, you’re going to need a way to flout the immune system. The wasps in the video above accomplish this through a very strange symbiosis: they inject viral particles into the caterpillar to knock it’s immune system out.

These viruses are very strange because they contain very few viral genes. Many of the genes they contain are actually very similar to the immune system of the wasp. They don’t replicate, but they travel to certain points of the fat body and nervous system and begin producing proteins which have a great many functions, from increasing the amount of food the caterpillar consumes to producing proteins which interfere with immune functions.

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Joe Ballenger is an entomologist who works in the biotech industry as a contractor. In his spare time, he helps answer questions about bugs at Ask an Entomologist. https://askentomologists.wordpress.com/