Adult lily leaf beetle (Coleoptera). L. Tewksbury, URI, Bugwood.org
Lily leaf beetle larva (Coleoptera) under a protective cover of its own excrement. R. A. Casagrande, URI, Bugwood.org
Holes in the leaves of true lilies (Lilium) eaten by by lily leaf beetles (Coleoptera)
Feeding damage from lily leaf beetles (Coleoptera) to the leaves of true lily (Lilium)
Overview
The lily leaf beetle was first seen in North America near Montreal, Canada in 1945 but was not seen in the United States until 1992 when it was discovered in Massachusetts. The beetle spread rapidly and is now in most of the New England states. It is not known from Missouri but since it is a strong flier and hides in infested plants, there is a concern that the beetles may spread to other areas. Originally from Europe and Asia, the beetle is not as destructive there where it is controlled by natural predators.
Adult lily leaf beetles are scarlet red with a black head, antennae, legs, and undersurface. It is about ½ inch long and will squeak when picked up and squeezed gently. The eggs, which are very tiny, reddish-orange, and laid in narrow irregular rows, hatch into bright orange, brown, yellow, or green 3/8 inch long larvae. The larvae are slug-like and produce a fecal shield by covering themselves with their own excrement, probably to deter predators or as camouflage.
Lily leaf beetles feed on a variety of plants including Solomon’s seal (Polygonatum sp.), potato (Solanum tuberosum), flowering tobacco (Nicotiana sp.), hollyhock (Alcea), and hostas, but their primary host plants are the true lilies (Lilium sp.) and fritillarias (Fritillaria sp.), the only plants where the adults will lay eggs. Daylilies are not host plants. Leaves are the preferred food although buds, flowers, and stems are also consumed, completely defoliating and eventually killing the plant. Both larvae and adults feed; larvae cause the most damage since hundreds may hatch at once.
Life Cycle
Lily leaf beetles overwinter as adults in plant or soil debris. They emerge in spring and after mating, the female lays up to 450 eggs on the underside of lily or fritillaria leaves. After 7-10 days, the eggs hatch, the larvae feed for 2 to 3 weeks, and then drop into the soil where they become fluorescent orange pupae. Adults will emerge from the pupae in 2 to 3 weeks, feed until fall and then overwinter.
Integrated Pest Management Strategies
1. Sanitation. Carefully inspect any plants being transported from infested areas since beetles will hide in plants and soil.
2. Handpick. If the number of beetles is small, handpick them and drop them into a container of soapy water or water with vegetable oil on top. Placing a light-colored cloth under the plant may help in finding adults that drop to the ground since they fall on their backs and their dark underside is hard to distinguish from the soil. The larvae may also be handpicked although due to the fecal shield, this may be an unpleasant and slippery task.
3. Use insecticides. If the infestation is severe, apply Neem oil, an insecticide that will kill larvae and repel adults. Most effective early in the growing season, it will need to be applied every 5-7 days.
4. Use a systemic insecticide. The systemic insecticide imidacloprid may be applied to the soil in spring or used as a foliar spray and has been reported to be effective late in the year.
Organic Strategies
Strategies 1 and 2 are strictly organic approaches. For an organic approach to Strategy 3, consult the Organic Materials Review Institute (OMRI™) for appropriate Neem products.