Poplar tentmakers are light brown to nearly black caterpillars with 4 light yellow lines along the back and a bright yellow and several indistinct lines along each side. There are black tubercles on the back of the first and eighth abdominal segments. The larvae live together protected by leaves pulled together and secured with silk. Small larvae feed on the leaf surface, large larvae leave only the petiole. Full grown larvae are about 1.3 inches long.

Oystershell scales are about 1/10 inch long and resemble crusty accumulations of oyster shells on the bark. Their drab, bark-like appearance makes them easy to overlook, even on close inspection. Heavy infestations can kill twigs or branches. This scale overwinters in the egg stage under the waxy covering of the female. The eggs hatch and the crawlers are active from late May to early June.

Aphids are soft-bodied insects that use their piercing sucking mouthparts to feed on plant sap. They usually occur in colonies on the undersides of tender terminal growth in the spring. Heavily-infested leaves can wilt or turn yellow and senesce prematurely because of excessive sap removal. While the plant may look bad, aphid feeding generally will not seriously harm healthy, established trees. Some plants are very sensitive to feeding by certain aphid species. Saliva injected into plants by these aphids may cause leaves to pucker or to become severely distorted, even if only a few aphids are present. Also, aphid feeding on flower buds and fruit can cause malformed flowers or fruit.

Aphids produce large amounts of a sugary liquid waste called "honeydew". The honeydew that drops from these insects can spot the windows and finish of cars parked under infested trees. A fungus called sooty mold can grow on honeydew deposits that accumulate on leaves and branches, turning them black. The appearance of sooty mold on plants may be the first time that an aphid infestation is noticed. The drops can attract other insects such as ants, flies, and wasps that will feed on the sticky deposits. For more information, see Entfact 103.

Twig pruners are the larvae of small beetles that tunnel in twigs and small branches. Female beetles lay their eggs about the time of bud break in the spring. Eggs are laid in small holes which are chewed into the bark. The larvae that hatch from these eggs bore into and tunnel toward the base of twigs. In late summer, they chew concentric circles outward toward the bark then move toward the tip. The twig eventually snaps and falls to the ground. The larva pupates in the fallen twig and emerges as an adult in the spring. Collecting and destroying fallen twigs can help to reduce infestations.

The Cottonwood borer is a large (nearly 2 inches long) black and white longhorn beetle. It is occasionally mistaken for the Asian longhorn beetle due to similar coloration. Females lay their eggs in August at the base of host plants and larvae will bore into the tree. Larvae are legless roundheaded borers that are up to 1.5 inches long. Development takes between 2-3 years beneath the bark. Damage is rarely threatening to the tree, though girdling can occur.

Poplar petiole gall is a growth caused by small gray aphids with a waxy appearance that live inside the gall. The hard galls are green, eventually turning red. Aphids leave the galls in mid-summer and move to another host plant. The leaves are not damaged by galls. Ants are often seen around the galls.