British Instructional Films Ltd production.
Moving landscape shot. River with mountains either side. Pine tree forests. C/U of a woodwasp boring a hole in a tree trunk. She lays her eggs in the hole. C/U of a grub eating away at the tree. Grub boring through tree. Tunnels it makes ruin the timber. The grub turns into a pupa. C/U of pupae. Turns into a woodwasp, discarding its pupa skin in the tunnel behind it as it crawls out. We see the woodwasps emerging from the tree. C/U of the holes made in the surface of the wood. British scientists study the woodwasps. C/U of microscope. Scientist looking through. Parasite which destroys the woodwasp is bred in British laboratories then sent around the Empire. Parasite - a rhyssa - is packed in moss then liberated in trees. C/U of the parasite crawling over tree bark. The parasite can tell where the wood wasp grub is inside the tree. We see the parasite drill down into the tree. It lays an egg on the pupa after injecting it with anaesthetic to make it lie still. Parasite then looks for another victim.
Egg of the parasite in C/U. Egg under a microscope. We see the jaws of the insect being formed. Young parasite grub leaves the egg and moves away. The grub crawls over the woodwasp pupa to find a good place to munch on. The parasite grub is seen in C/U, the narrator suggests that it looks rather like a judge! Empty shell of the woodwasp grub (it has all been eaten by the parasite). Parasite makes its way to the surface of the wood. We see it emerge from a hole in the bark. Shots of the river. Commentary describes the war between woodwasps and parasites.
Note: see also - "The Sirex Woodwasps and their Insect Enemies" from which most of this material is taken.