The imported willow leaf beetle was first detected in the United States in 1911. Adult beetles range in color from nearly black to greenish blue. Adults are approximately 3/16 of an inch in length and convex oval in shape. Adults overwinter in loose bark or other sheltered areas on or near the tree trunk. In the spring, shortly after leaves open, adults emerge to feed on the foliage and lay tiny, yellow eggs in clusters on leaf undersides. In a few days, the eggs hatch and tiny, dark colored larvae begin to skeletonize the leaf undersides as they feed. As larvae grow in size, they may be found on both leaf undersides and surfaces. Mature larvae may be up to 1/4 inch long. After approximately 3-4 weeks, larvae will pupate before transforming into adults. Pupae are said to be yellowish-brown in color with dark markings. The exact timing and location of pupation in Massachusetts is not completely understood. In parts of Virginia and North Carolina, there may be 4 generations per year. In New England, 2-3 generations may occur per year.
For video footage of the life stages and life cycle of this insect, visit: InsectXaminer.
Can be an important pest of willows and poplars, particularly smaller plants. However, management is rarely deemed necessary, especially for established trees that tolerate yearly feeding. Both surfaces of leaves may be impacted on most willows. Larvae skeletonize the leaves while the adults chew holes in the foliage from the upper surface. Affected willows may appear bronzed by mid- to late summer. The larvae are said to cause the majority of the damage to host plant leaves.
Monitor for adults in the spring as soon as new foliage becomes available. Shortly thereafter, look for groups of yellow eggs on leaf undersides (not to be confused with certain lady beetle eggs). Search for skeletonization (larvae) and notching (adults) of leaves.
Some studies suggest that air pollution, such as increased exposure to ozone, may result in leaves being more frequently fed upon by this insect (Johnson and Lyon, 1991). Adults, eggs, and larvae may be too abundant to mechanically manage.
Schizonotus sieboldi (a parasitic wasp) is reported as a highly effective parasite of imported willow leaf beetle pupae. For example, at a study site in New York, S. sieboldi is said to have parasitized 50% of second generation pupae (Johnson and Lyon, 1991). Additional parasitoids and predators are noted for the imported willow leaf beetle, including lady beetles, lacewings, predaceous bugs, and spiders. Additional natural enemies of European and Asian origin are discussed for the imported willow leaf beetle in the Invasive Species Compendium (CABI) but these organisms may not all occur in the United States.
Acephate (larvae) (NL)
Azadirachtin (NL)
Chromobacterium subtsugae (NL)
Clothianidin (NL)
Cyantranilprole (NL)
Dinotefuran (NL)
Flonicamid+ cyclaniliprole (N)
Horticultural oil (L)
Imidacloprid (L)
Lambda-cyhalothrin (L)
Permethrin (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Take care with insecticide applications in areas near water.
Active ingredients that may be applied systemically include: acephate (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), and imidacloprid (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
