If people here can get all thin-lipped about a single apple (do any of you work for airport security, by any chance?) - I'm surprised you're not incandescent about the huge leaking bags of alien microbes that get let through customs by the million every day. They're called humans.
Do you know how much of YOU is actually not you at all, but bacteria, viruses, fungus and other alien lifeforms? (Answer: less than half.) You may put your apple virtuously in the cc's garbage bag, but as soon as you visit the airport toilet for a crap, you're releasing a bunch of stuff (including seeds - this is why tomato plants luxuriate around sewage outlets) into the local ecosystem that originated somewhere not local at all.
Ban people from travelling by air. Go on, you know you've always wanted to...