Answer: The lily beetle is a serious problem, in part because they can fly in as well as breed on and near the lilies. Most gardeners resort to a multi-pronged approach. Carbaryl (the active ingredient in Sevin) will kill adults but only on contact -- there is no residual action, or you can hand pick the adults. Neem based sprays can control the larvae, be sure to spray top and bottom sides of the foliage. The egg masses on the undersides of the leaves can be pulled off by hand. Since this pest overwinters in the soil, some gardeners also lightly disturb the soil around the lilies in very early spring to try to stop them then as well. I wish I could be more encouraging.
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