The lily leaf beetle (Lilioceris lilii), also referred to as the red lily beetle, may be attractive with its fiery-red coat, but without intervention it can defoliate your lilies (Lilium spp) in days. Lilies thrive in well-drained soil in a sunny location and can be grown in U.S. department of Agriculture plant hardiness zones 2 through 9, depending on the cultivar. Just one adult female can lay more than 450 eggs in the course of one or two seasons, making controlling the adults and preventing further breeding an important step in preventing the damaging effects of these tiny beetles on your lilies.
Lily Leaf Beetle Life Cycle
Because the adult lily beetle overwinters in the soil or sheltered areas of the yard, they arrive in the garden in the spring as soon as your lilies begin to grow. They soon mate and lay rows of tan eggs that deepen to orange or red as they mature. Eggs are deposited on the undersides of the leaves where they may go undetected. The red-shelled adults are relatively light eaters, but the larvae have a veracious appetite and begin to devour the foliage as soon as they emerge. Feeding typically occurs from the ground upward, stripping the stem of leaves and even attacking the flower buds. Larva feeding lasts for 16 to 24 days at which time the larvae drop to the soil to pupate. They emerge as adults in 16 to 22 days and begin the cycle anew.
Handpicking the adult beetles from your lilies is an effective method of control if they do not fly away in the process. Holding a bucket filled with 3 to 4 inches of soapy water under the foliage of the lily and tapping the stalk generally causes the lily beetles to drop into the bucket where they soon drown. Examining your lily foliage as soon as it emerges from the soil, checking the undersides and stems carefully for the presence of eggs, allows you to address problems with the lily beetle before damage occurs. Removing and crushing the eggs prevents the emergence of hungry larvae.
Several insecticides are effective against lily beetles explains the University of Rhode Island Plant Sciences Department. Both carbaryl and malathion kill the adult and larva of the lily beetle, but they do so at some risk to other insects. Carbaryl is toxic to bees and may pose problems with pollination of other crops in your garden if bees are killed. Malathion is toxic to other beneficial insects, as well. Neem, derived from the neem tree, is a safer alternative, and is effective in killing larvae and repelling adult beetles. Neem is available as foliar spray, fertilizer stakes or soil drenches, and must be applied every five to seven days once the eggs begin to hatch.
The University of Rhode Island Biological Control Lab is conducting research to develop biological controls against the lily leaf beetle. The use of parasitic insects, such as a small wasp (Tetrastichus setifer) are being assessed as the lab conducts the Lily Leaf Beetle Biological Control Survey 2013. Gardeners throughout New England are asked to send samples of larvae feeding on their lilies for dissection and testing for the presence of the parasitic insects. Biological controls are not yet available to the public, but have proven effective in controlling the lily leaf beetle in Europe.