Necessary, because if it were not true — if using the genetically engineered crops will NOT cause less harm to wildlife populations — then we have no reason to think using the crops more widely would “help wildlife populations recover.” Replacing current crops with crops that cause just as much harm wouldn’t help recovery.

Not necessary, because the harm to insecticides results from “excessive spraying.” Although the author does assume that if the spraying were not “excessive,” wildlife would benefit, that doesn’t imply the author thinks only a slight reduction in spraying would benefit. A slight reduction can still be “excessive spraying.”

Not necessary, because the author just needs to assume that these crops won’t be subject to “excessive spraying.” If the crops are sprayed a tiny amount, but not excessively, that wouldn’t undermine the author’s reasoning.

Not necessary, because the argument’s reasoning doesn’t concern which kind of crop is more expensive to use.

Not necessary, because if there are other reasons that wider use of the crops could help wildlife recover, that doesn’t undermine the author’s reasoning. As long as preventing excessive spraying is one of the reasons that the crop can help wildlife recover, the author’s argument can still work.