I grow a few lilies and there is a systemic insectiside which kills the grubs as soon as they hatch. I don't use it as I don't use chemicals but i will track it down for you if you want. I just watch my lilies carefully and as soon as I see the red beetles I kill them. I hold an open jar under the leaf with the beetle on it then tap above it and it drops straight down usually into the jar then I squash it. I search the plant for eggs (small, orange normally under a leaf) and squash them too. I very rarely get the disgusting grubs but those I wipe off with kitchen paper towels and squash again. Yes it does take time and I only have about 30 lilies. I have yet to find a non chemical method of killing these bugs, I will be interested to see if anyone else comes up with something.