Leaf Feeders
Milan Zubrik, Forest Research Institute - Slovakia, Bugwood.org
Fall webworms are small hairy white caterpillars that live communally in thin silken webs at the ends of branches. They may leave the tent to feed individually as they get larger. While the webbing is unsightly, feeding damage is usually limited to limbs around the tent. Large established trees are not seriously affected by small to moderate infestations. The larval stage feeds for 4 to 8 weeks and may be found on a variety of hardwoods. The first generation occurs in late May and early June, the second generation is usually larger and active from July through September. For more information, see Entfact 424.
David Cappaert, Bugwood.org
Imported willow leaf beetles are small oval metallic dark blue-green beetles that chew small holes in newer leaves or notches in the leaf margins from April to May. The elongate black-green larvae chew partly through older leaves giving them a skeletonized appearance. There are two generations each year; adults spend the winter in protected places.
A. Steven Munson, USDA Forest Service, Bugwood.org
Mourning cloak butterfly caterpillar is black with many fine white specks and larger red-brown spots on its back. There is a double row of thin barbed black spines down the back, also. Small groups of larvae may be found feeding on the foliage.
Lacy L. Hyche, Auburn University, Bugwood.org
Willow sawflies are black caterpillar-like insects with yellow spots along their sides and black heads. The first generation is active in May, a second occurs in July. They spend the winter as pupae in the soil around host trees.
Lacy L. Hyche, Auburn University, Bugwood.org
Cottonwood leaf beetle is a pest both as an adult and as a larva. The larvae will feed by skeletonizing leaves, while adults feed along veins and the midrib. Larvae are black when they first emerge and lighten in color as they age; they can also produce a pungent odor from spots along their back. Adults are yellow-orange with black stripes and spots along the back. They overwinter as adults and emerge in the spring to lay eggs on host plants. There are multiple generations per year, with damage occurring throughout the growing season.
Sap Feeders
John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org
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.
Sturgis McKeever, Georgia Southern University, Bugwood.org
Cottony cushion scale is an invasive scale species that can be found feeding on the sap of numerous species of plants. Adult females are orange-brown but coated with white wax and will have a long, fluted egg sac attached to the body. This can contain up to 1,000 eggs. After hatching, the nymphs (which are red with dark antennae and legs) will seek a suitable space for feeding. Nymphal feeding on leaves can cause extensive damage and honeydew/black sooty mold will accumulate as the population builds.
Borers
James Solomon, USDA Forest Service, Bugwood.org
Carpenterworms are reddish pink caterpillars that tunnel into the bark and wood of oaks, especially red oaks and a number of other hardwoods. Their damage causes unsightly scars on ornamental trees and degrades rough sawn lumber. Eggs are laid in bark crevices or under vines and lichens. Small larvae feed into the phloem and cambium but soon chew into the sapwood. Fine frass mixed with sap is ejected from the entrance hole in the bark and builds up at the base of the tree as larvae hollow out galleries beneath the bark. Infested trees usually are not killed but long term attacks may weaken trees structurally.
Jim Baker, North Carolina State University, Bugwood.org (adult)
James Solomon, USDA Forest Service, Bugwood.org (larva)
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.