How do you control red beetles that like lillies?

You will have spray them down continually with a insecticide spray.

Dust with food grade Diatomaceous Earth. Dust the plants & the ground around the plants (dusters just for Diatomaceous Earth make it soooo much easier). You will have to redo this every time the plant gets wet. After you kill the present infestation you will only have to do it when you see new indications that they are back. Just know that Diatomaceous Earth kills all bugs.

it does but it is the same control having to do it repeatedly.

I place cotton balls soaked in Tea Tree oil around the plants, keeps rodents away too!! also you can make a spray of 20 drops of Tea tree oil to a pint of water( add a few drops of liquid dawn to disperse oil if needed) and this kills all bugs....bedbugs too! It melts the hard shells of bugs. ...poor bugs. Hope this helps