Answer: This beetle is a recent arrival to the U.S., and you're located in one of its hot spots. If you see the adult beetles, pick them off and drown them in a cup of soapy water. To control the crusty, yellow-black larvae, you need to spray weekly from May through June with a product containing neem oil, such as BioNeem. It's kind of late to try and catch them this year, but you'll be prepared for them next spring!
Here's the beetle's life cycle - this may give you more insight on how else you might prepare for it's emergence, or even inhibit emergence: The adult beetles overwinter in the soil and emerges from soil in April as lilies begin to grow. Beetles feed on tender new growth and lay a string of red eggs on the underside of leaves. When the larvae emerge, they feed mostly on the undersides of leaves, creating notches and holes. Feeding often results in deformed blooms. Neem oil will only kill larvae if it's applied soon after the eggs hatch. Perhaps some shallow cultivation in late summer will uncover the pupating larvae and expose them to predation. I also wonder if they are affected by beneficial nematodes? It may be worth a try! Good luck!
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