Lilies have long been favored by gardeners in the Northeast for their unsurpassed beauty and relative ease of maintenance. The recent arrival of the lily leaf beetle in Boston has complicated lily culture and gardeners throughout the area should be on the lookout for this insect. The lily leaf beetle, native to Europe, was discovered near Montreal, Canada in 1945. Its damage was limited to the Montreal area for decades, but recently it has spread to the south and west. The beetle was first officially sighted in Cambridge, Massachusetts in the summer of 1992. Many gardeners in the area believe it came in with bulbs shipped from Europe. The beetles are strong fliers and excellent hiders. They have spread as much as 150 miles from Boston, in many cases with the assistance of gardeners. At present the infested area in the USA reaches into all of the New England states, including southern Connecticut and northern Vermont. Not all areas are yet infested and gardeners who are transplanting bulbs and other garden plants should be careful not to move these beetles to an uninfested area.

Lily leaf beetles will taste or feed lightly on many plants including Lilium spp., Fritillaria spp., Polygonatum spp. (Solomon's seal), Solanum dulcamara (bittersweet nightshade), S. tuberosum (potato), Smilax spp., Nicotiana spp. and other plants. However, they will only lay eggs and develop on Liliuim species (Turk's cap lilies, tiger lilies, Easter lilies, Asiatic and Oriental lilies), and species of Fritillaria.

Description and Life Cycle:

The lily leaf beetle adult is a striking insect with a bright scarlet body and black legs, head, antennae, and undersurface. The adults are 6 to 9 mm (1/4 to 3/8 inch) long, and they will squeak if they are squeezed gently--a defense mechanism to deter predators. Adults and older larvae feed on leaves, stems, buds, and flowers of the host plant. Adults lay their eggs on the underside of leaves in an irregular line. The reddish/orange eggs take from 7-10 days to hatch under normal conditions. Females lay up to 450 eggs, sometimes over two growing seasons. Larvae resemble slugs with swollen orange, brown, yellowish or even greenish bodies and black heads. Larvae tend to cause more damage than adults. Larvae are distinctive and repulsive in that they secrete and carry their excrement on their backs. Younger larvae feed for 16-24 days, primarily on the underside of leaves. Larvae 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 in late March through June. Lily leaf beetles overwinter in the soil or plant debris in the garden or woods, sometimes a distance away from the host plants. Adults prefer environments that are shaded, protected, cool, and moist.

Control:

If you only have a few plants in your garden, hand-picking adults and eggs can be effective (we prefer not to handle larvae, although there is no danger in doing so). 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. To date, our material of choice for treating flowers is neem, an insecticide based upon extracts from the neem tree. Neem can be purchased at garden centers under the trade names Turplcx, Azatin EC, Margosan-0, Align and BioNeem. Neem kills larvae and repels adults. Neem is most effective on first instar larvae; it must be applied every five to seven days after egg hatch. The insecticide imidacloprid also provides effective control. It is available in several formulations from Bayer including foliar sprays, soil drenches, and fertilizer stakes.

Recent efforts to control the lily leaf beetle have concentrated on biological control. The lily leaf beetle is under good biological control in France and Switzerland, where at least four species of parasitoids attack it. We have released one species of European parasitoid in Boston, MA and Cumberland, RI, and we are conducting basic experiments on parasite biology and host specificity with the other parasitic insects in our quarantine laboratory on campus--perhaps eventually leading to additional releases in the USA.

University of Rhode Island Plant Sciences Department, 2002