The female lays her yellow eggs on the undersides of leaves in clusters of 25 or more. As the small, black larvae hatch, they feed on the underside of the leaf and generally pupate in two weeks. The larvae attach themselves to twigs or leaves, hanging upside down to pupate. Hosts Cottonwood leaf beetles are serious pests of poplars, aspens, elders, and willows. The young larvae live in groups and skeletonize the undersides of leaves before eventually separating and consuming all but the large leaf veins.
Adults chew holes in the leaves and attack new shoots, causing stunting and multiple-branched trees.
The beetles also feed on the young bark of seedlings, causing severely stunted growth and death. Cottonwoods and other suitable hosts are most severely damaged within the first three years of growth. Fall applications generally are not warranted. Inspection and Control Ants, ladybird beetles, lacewings, spiders, wasps, and various parasites feed on cottonwood leaf beetle larvae and eggs, offering some natural controls. When populations reach action threshold levels, insecticide applications may be necessary.