have you taken off the larvae? they look like splogs of bird poo and they hide in this sliey sectretion. wipe all the leaves and squish any you find.

could also be slugs of course.

Those Red Lily beetles are so persistent. I have one poor little remnant of a once stately Regal Lily, and still they chew at it. I was hoping they would eat themselves out of house and home, but no such luck. No revolting larvae seen so far. Nothing left for them anyway!!!

Slugs love lilies. If it's not the larvae it's probably slugs.:(