Is this insect beneficial or a pest?
This is the Lily Leaf Beetle
Known to lay its eggs and develop only on true lilies, Lilium species (Turk's cap lilies, tiger lilies, Easter lilies, Asiatic and Oriental lilies) (not daylilies), and fritillaria (Fritillaria sp). These beetles have been known to feed on a number of other plants, including lily of the valley (Convallaria majalis), soloman's seal (Polygonatum sp.), bittersweet (Solanum sp.), potato (Solanum tuberosum), hollyhock (Alcea) and various hosta species.
The adult beetles are about ½" long with a very bright red body, and black legs, head, antennae, and undersurface. The beetles are foraging for food and seeking a mate. The adult beetles will begin to lay eggs on the undersides of leaves, usually in May. The eggs are irregular-shaped and laid in rows that appear as tan-colored lines. Just before the eggs hatch, they will turn orange and then a deep red color. The eggs hatch within 4-8 days into the immature or larval stage. The larvae are slug-like in appearance with soft, plump orange, brown, yellowish or even greenish bodies and black heads. The young larvae initially feed on the undersides of the foliage but eventually will move to the upper surfaces and the buds. While they feed, the larvae pile their own excrement on their backs which makes them objectionable to hand-pick. The larval feeding is the most destructive and lasts for 16-24 days. Each female beetle produces 250-450 eggs.
Hand-picking adults and eggs can be effective. For more than a few susceptible plants, pesticide treatments may be needed. Products containing Neem (Bon-Neem, Azatin), a botanical insecticide, have been shown to kill very young larvae but must be applied every five to seven days after egg hatch. Before applying any pesticide, READ THE LABEL and apply only as directed on the label.