Answer: the destruction of the butterflies’ environment
Step-by-step explanation:
A mutation that would result in darker wings will mean that the birds that prey on them will stop eating a lot of them so this won't lead to extinction.
A decrease in the birds that eat the butterflies will also mean that the butterflies will survive more because they will have less predators.
Overproduction of butterfly offspring means more butterflies so they will not go extinct.
If their habitat was destroyed however, the butterflies might find it hard to survive as any new environment they go to might not be suitable leading to their extinction.