radiation, freezing ...

Right. my guess is there are a lot of species involved. Some may well be space faring invulnerable sorts who regularly inhabit toughened spore states. Ultra freezing and radiation are about the only things i can think of that stand a chance of killing off enough to make a good chance of stopping recurrence. But i haven't found anyone who has tested it yet. Radiation might be pretty good for what inhabits the glue though. Assuming there is an effective part of the spectrum which optical glass is transparent to.