Hosts poisoned

Hello everyone,
I've had 25 caterpillars of California memnon.
A few weeks before, I found 2 big musa plants.
But when I gave the caterpillars the plants, they almost all died..
When I gave the ones that stood alive, an other plant that I found, but not from a garden centre.
Those did stay alive and were become butterflies.
So I think the plants were poisoned.. Does someone know what you can do to get the poison
from the plants (if that's possible in some way)??

Thank you very much,
Henk

That's good to know!! Thank you