Background and Life History

The elm leaf beetle (ELB), Xanthogaleruca luteola, was accidentally introduced from Europe into the eastern United States in the 1830's. The beetle was not found in California until the 1920's and can now be found almost any place where there are elms. There are no native elms in California, but it is estimated that 2.5 million elms have been planted in the state. ELB is the most important pest of elms in California; it is ranked as the second most important urban tree pest in the western United States and third nationwide (Wu et al., 1991).

The beetles overwinter as adults in sheltered places such as wood piles, garages, attics, etc.. In the spring, the adults emerge from their hiding places and feed on the foliage for one to two weeks before starting to lay eggs. Adult feeding is characterized by small circular, BB-size holes in the foliage. Eggs are yellow and oblong and are laid in clusters of 15 to 20. The larvae, which are the most damaging stage, develop through three instars [A]. Larval feeding skeletonizes the foliage, often causing the leaves to drop [B]. When ready to pupate, the larvae crawl into holes in the trunk of the tree, limb crotches, beneath loose bark, or to the base of the tree [C]. Depending on climate, there can be one to three generations per year in the northern part of the state and even more in southern California. The larval stage is usually the focal point for chemical control efforts.