Elm Leaf Beetle. Life Cycle and Habits Elm leaf beetles overwinter as adults in homes, buildings, wood piles, tree bark crevices, debris at the tree base and other protected places. Egg-laying begins in late May and early June, with each female laying between 400 and 800 eggs over her life span. Eggs hatch in about seven days. Small, black larvae feed on the leaves and mature in two to three weeks.
Young larvae feed in groups and older larvae sometimes singly.
Pupation occurs in tree bark crevices or on the ground in sheltered places, with new adults emerging about 10 days later. There are two or more generations per year depending on the season. Both adults and larvae feed on the elm foliage. Adults chew small, round, irregular holes in the leaf, whereas the larvae skeletonize, leaving only the vein intact. When damage is severe, leaves curl, dry out and fall prematurely.