Lili Leaf Beatle

The lily leaf beetle is an imported pest that will only lay its eggs on true lilies; researchers in Rhode Island have found it feeding on such other host plants as Soloman’s seal, bittersweet, potato, hollyhock, and various hosta species. This pest does not attack daylilies. It was first discovered in the United States in 1992 in Cambridge, Massachusetts. Most likely, it arrived in a shipment of lily bulbs from Europe. These beetles are strong fliers and can also be moved from one area to another on host plants. Both larveand  adults are capable of causing great harm to host plants, although larvae tend to cause more damage.

The infested area reaches into all of the New England states, including southern Connecticut and northern Vermont. Since not all areas are yet infested gardeners who are transplanting bulbs and other garden plants should be careful not to move these beetles to an uninfested area.

They will squeak if they are squeezed gently – a defense mechanism to deterpredators. Adults prefer environments that are shaded, protected, cool, and moist.

Description and Life Cycle

The adult lily leaf beetle is a striking insect with a bright scarlet body and black legs, head, antennae, and undersurface. The adults are about ½ inch long. Their appearance is quite noticeable. Larvae resemble slugs with swollen orange, brown, yellowish or

even greenish bodies and black heads. Larvae are distinctive and repulsive in that they secrete and carry their excrement on their backs. Adults overwinter in secluded, sheltered places. They emerge from late March into June and begin to forage for food and seek a mate. Adult females lay their eggs on the underside of leaves. The eggs take from 7-10 days to hatch, under normal conditions.Younger larvae feed for 16-24 days, primarily on the underside of leaves, and then enter the soil to pupate; pupae are florescent orange. New adults emerge in 16-22 days and feed  until fall. They do not mate or lay eggs until they emerge the following spring. Lily leaf beetles overwinter in the soil or in plant debris, sometimes a distance away from host plants.

Control

When only a small number of plants are infested, these pests can be removed manually. However, when many susceptible plants are attacked, applications of pesticides may be warranted. The insecticides carbaryl (Sevin) and malathion are effective on adults and larvae. However, carbaryl is highly toxic to bees and malathion is also toxic to many non-target insects. Neem, a botanical insecticide based on extracts from the neem tree, kills young larvae and repels adults. It must be applied every five to seven days after egg hatch. The insecticide imidacloprid also provides effective control.

Adapted from: University of Rhode Island Plant Sciences Department, 2002; UMass Extension