“ The females mutated and were unable to breed with the males. Over the next 35 years, the species spontaneously went extinct.”
There’s no reason to believe that all female locusts had mutations that made them unable to breed.
The author of that book believes movement into the locusts’ core areas by farmers changed the local environment so much that they died out. That’s much easier to believe than a sudden, wide-spread, but specific mutation caused the entire species to go extinct.
He dissected locust that he found frozen in glasiers. That is how he came to his conclusion.