Cottonwood leaf beetle

Adults and larvae of the cottonwood leaf beetles feed on foliage of poplars, willows, aspens, and alders, sometimes causing severe damage to the trees. Young larvae feed together and skeletonize leaves. Older larvae and adults feed individually, chewing holes or consuming entire leaves, except for the larger veins. The quarter-inch adults are usually yellow with a distinctive pattern of black, longitudinal stripes, although the elytra of some individuals may be almost completely yellow or black. Larvae, which give off a pungent odor when disturbed, are black when young and become brown as they grow. After feeding for about 2 weeks, they pupate on leaf surfaces, bark, or weeds and grasses beneath host trees. The pupa hangs from vegetation with the head end down. In southern states, there are 6 to 8 generations per year.

Links:

New Mexico State University: Managing Cottonwood Leaf Beetles