Cottonwood, Poplar and Willow
Appearance and Life Cycle
Adult beetles are approximately 6 millimetres (mm) long. The margins of the beetle are red, the head and thorax are black and the abdomen is yellow with black interrupted stripes. Adults overwinter under debris beneath host trees. They emerge in early spring and feed on unfolding leaves or tender buds and twigs. After mating, females lay eggs in groups of 15-75 on the undersides of leaves. Each female can lay up to 800 eggs. The eggs are elongated-oval, yellow and approximately 1 mm long. Larvae hatched from the eggs are black at first and change to a dirty yellow colour. Full grown larvae can reach 10 mm in length. Mature larvae attach themselves to leaves, bark or weeds and grass beneath host trees where they pupate. Pupae are yellowish-brown with dark spots and are approximately 7 mm long. There are several generations a year which may cause damage.
Both adults and larvae feed on opening foliage. Larvae skeletonize leaves at first, but later they consume entire leaves, leaving only the large veins. Extensive feeding may result in stunting, excessive forking or even death of the tree. If adults are abundant in early spring, feeding may delay bud break.
Insecticides for the control of cottonwood leaf beetle include: carbaryl; deltamethrin and malathion. Insecticides should be applied when beetles are first noticed and repeated in 10 days to control newly emerged larvae and adults.