The lily leaf beetle, Lilioceris lilii, is native to Europe. It migrated to Canada and then invaded the United States in the 1990s. The bug is very mobile and a strong flier. The immature beetle and the adult feed on leaves and buds. They are capable of defoliating an entire plant. Adults over-winter in the ground and attack the lilies as soon as they emerges in spring. The adult beetle measures 1/2 inch in length and has a red body and black legs.
Beetles lay eggs on the underside of leaves in rows that appear as tan lines. The hatched larvae look like slugs and have orange, brown, yellow or green bodies and black heads. They feed on the undersides of the leaves before moving to the top and buds of the lily. They pupate in less than a month and a new generation of adult beetles emerge to continue feasting on the plant.
Aphids, armored scales, bulb flies, bulb mites, carrot beetles, cucumber beetles, hoplia beetles, leaf miners, nematodes, snails and slugs, spider mites, thrips, weevils, and whiteflies are all known pests of the lily plant, according to the University of California Statewide Integrated Pest Management System. Scale insects, aphids and whiteflies feed on the sap of the lily.
Blessed with a wide range of colors, the flowers of the lily plant may be spotted or have other distinct markings. In cool climates, the lily should be planted in full sunshine, while partial shade is a necessity for warmer geographic locales. They appreciate rich, well-drained soil and require regular hydration through the growing season. Organic mulch helps to maintain a moderate soil temperature around the lily.
Diseases afflicting the lily include gray mold, root and stem rots, rusts and viruses.