and Life History
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).
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.