One of the most useful things for catching and killing lily beetles is an old tea strainer - preferably not the one you use for your earl grey! Keep it in your pocket and catch the beetles in it before they hit the ground and are never seen again. Carry them to hard standing and JUMP on them as hard as you can!! This needs doing daily, or even twice a day in season, and really does help, besides being very satisfactory when you kill them. I grow literally hundreds of lilies, both in pots and in the ground and only vigilance works. If you want to use chemicals, provado works for a season, but the larvae will come back the next year - I'm afraid we are stuck with them until the birds or something like that recognises them as prey- unlikely with that red coloration.