LIFE CYCLES
START
INTERWOVEN
10.5mm
2
0
The parasitoid’s reproductive tract is filled with virus particles. When she injects an egg into the caterpillar, about one billion virus particles get squeezed in along with it.
12mm
Wasp Egg
Caterpillar
Larvae are vulnerable to being parasitized during their 2nd to 3rd growth stage (instar). Their bodies are soft and tender, and they’re too small to fight back.
Virus Particles
The female parasitoid jabs her long ovipositor into a caterpillar. She injects an egg, along with some thick fluid that’s filled with venom and virus.
Intersection
Wasp reproductive tract
9mm
Virus
EXIT
Soybean Looper: Egg
The eggs are on the undersides of leaves, protected and out of sight. Inside, embryos develop.
Larvae hatch from the eggs and begin eating leaves. The larvae go through several growth stages, or
“in-stars.” Between each stage, it grows a new skin (really an exoskeleton) and sheds its old one.
Soybean Looper: Early Larva
Soybean Looper: Late Larva
A healthy larva will continue to eat and grow.
Larvae that aren’t parasitized keep eating and growing. They need to store lots of nutrients so they will have enough energy to complete metamorphosis. When the larva gets as big as it will get, it stops eating and starts wandering.
The larva crawls to a hidden place on the underside of a leaf. It spins silk to make a loose web around itself, which it uses like a basket or hammock. It sheds its skin one last time to reveal a pupal case. The larva is now a pupa. Inside, it goes through metamorphosis. Since it can’t eat during this stage, the pupa relies on the nutrients it stored as a larva.
Soybean Looper: Pupa
Soybean Looper: Adult
The pupal cases open and the adult moths emerge. They mate at night, then the females go to the undersides of leaves to lay their eggs. The adults live for only a week or so, feeding on nectar from grass or clover flowers.
Inside the caterpillar, inside the egg, the parasitoid embryo develops.
In each of the embryo’s cells, in the DNA it inherited from its parents, there’s a copy of the virus’s genes. The viral genes here aren’t active yet. But they include instructions for building virus particles.
Wasp Parasitoid: Egg
The virus particles from the parasitoid mother infect some of the caterpillar’s cells—mainly blood and fat cells. Inside the infected cells, viral genes get activated. Within 12-24 hours, the caterpillar loses its appetite and its growth slows.
Every time one of the parasitoid’s cells copies its DNA and divides in two, the embedded viral genes get copied along with it. Each of the parasitoid’s cells holds a copy of the viral genes—including in the ones that will form the ovary and reproductive cells. But the viral genes are not active…yet.
Viral genes
The larva hatches from the egg and begins feeding on the caterpillar’s blood (called hemolymph). It squirms around inside the caterpillar, stealing all the nutrients it needs. As the parasitoid grows bigger, you can see it. It looks like a dark spot near the caterpillar’s rear end.
With the virus active in it’s body, and with the parasitoid larva drinking its blood, the caterpillar stays small and weak. For now, it still eats a little. But it is quite sick.
Wasp Parasitoid: Larva
Parasitoid DNA
The parasitoid larva chews a hole in the side of the host and squirms out. It spins a cocoon around itself and becomes a pupa. Inside the cocoon, the parasitoid pupa goes through metamorphosis.
In the female parasitoid pupa, the ovary starts to take shape. The viral genes in its cells activate. Ovary cells fill with virus particles until they burst. The reproductive tract fills with sticky, virus-filled goo.
Sadly, the caterpillar dies.
Wasp Parasitoid: Pupa
After metamorphosis the adult parasitoids emerge. The female’s reproductive tract is already filled with virus. After mating, she will search for a caterpillar to parasitize.
The parasitoids’ reproductive cells (eggs and sperm) hold not only instructions for making a parasitoid—but also for making virus. This ensures that all their female offspring will be able to make virus particles, for generations to come.
Wasp Parasitoid: Adult
Explore the interwoven life cycles of three different organisms!
Viral gene
Caterpillar cell nucleus
Embryos maturing inside the eggs
Hatching larva
Young larva: about 8mm long
Newly-hatched larva
Eggs
1