Last summer (2013), we found lily beetle eggs on claspleaf twistedstalk Streptopus lanceolatus (shown below) in the Gatineau Park north of Ottawa just across the Quebec border. Although the larvae from the eggs we found failed to survive, we have nevertheless been quite successful rearing larvae on twistedstalk in the lab. Claspleaf twistedstalk is endangered in New Jersey and Pennsylvania.
If you see lily leaf beetles on other plants besides cultivated garden lilies and fritillarias, please let us know by submitting the form on the Report an Infestation page. Note that lily beetle adults will commonly rest on other plants without actually feeding on them. We are interested in reports of feeding or egg laying on new host species. When you're not sure whether the beetles are actually feeding on a plant, put a few of them in a jar with some undamaged leaves and see if they will feed. (This would make a great science fair project for kids!)
Looking forward to hearing about your observations!