Unfortunately, I don't know of any other treatments that you have not mentioned. In the Master Gardener training I took, the big long-term hope is the parasitic wasps that are supposed to be moving out from key sites in the New England region.

I think saying that they might be killing the pollinators may be understating it since for bees even relatively low doses interferes with their ability to navigate, so while it may not be outright death (though it may depending on doses) interfering with the bees' navigation interferes with their ability to feed, so it is good that you are reconsidering the use of this class of insecticide. It will stay in the soil for several years for many cases, so you may not have problems with the beetles this year, again depending on the soil levels.

I see just a few choices: lower level insecticides such as those you listed, mechanical removal of the beetles (something white under the plants before removal makes those that drop easier to see and doing the removal early morning when it's cool means the bugs move slower) - I knock pests into a container of soapy water, and removing the lilies or transplanting them into pots, keeping them in a screened area, and then taking them out just when blooming and placing the pots in the garden at that time. If you continue using the Imidacloprid, if the preditory wasps arrive, it may kill them as well.

The predatory wasps saved my tiger lilies, I was definitely not going to use insecticides, and for several years my tiger lilies were nothing more than withered stems, devoured by the red beetles. I had pretty much given them up for dead. Then they made a come-back a couple years ago, which I attribute to the wasps. I would advocate patience, and perhaps indoor pots for some of the more valuable lilies as NHBabs suggested.

Thanks for the responses! I used to manually remove the beetles back before my lily obsession spiraled out of control lol. I certainly cannot dig them up as they are in busy perennial beds with many neighboring plants but I think I will try using the lower level pesticides until the predatory wasp population finds its way to my garden. Does anyone know the current spread of these since their release into New England?

Again, thank you for taking the time to post :)

I'm attaching a link to the UConn Integrated Pest Management Program. At the end of the article is an interactive map showing results in Connecticut where I live. You might try writing to your state university to get similar information.....Integrated Pest Management Map.