This category includes those insects that insert their mouthparts into a leaf or twig and suck the juices from the plant. The tree's reaction is manifested by wilted or curled leaves, galls, defoliation, branch tip dieback, or reduced growth. Determining the cause of these symptoms usually depends on identifying the insect itself.

    Mites are tiny 8-legged, spider-like "bugs" closely related to insects. They have piercingsucking mouthparts and cause damage resembling that produced by sucking insects. Expert identification is often necessary to distinguish between the two.

VELVET GALL MITE,
ERIOPHYES CAULIS KEIFER

Description
    Little is known about the mites that occur on black walnut, but the velvet gall mite is common in some areas. The mite itself is so small that it cannot be seen with the unaided eye.

Injury
    The velvet gall mite causes a conspicuous velvety red growth up to an inch long on the leaf stem, often causing the leaf to curl or twist over on itself. Galls may be numerous on individual trees but they are considered to be harmless to the tree.

Control
    No control is recommended.

APHIDS OR PLANT LICE,
MONELLIA SP. AND MONELLIOPSIS SP.

Description
    Several species of aphids are found on black walnut. They are a common, widely distributed insect pest and occur wherever walnut is grown. They occur throughout the growing season on the undersurface of walnut leaves.

    Aphids are small, soft-bodied insects with pear-shaped bodies; they may be brown, green, white, or purple in color. Not all adult aphids have wings but when present the wings are transparent. The nymphs resemble the adults in color and shape but are smaller in size.

Injury

Aphids on black walnut

    Normally, aphids are sparse on black walnut and therefore probably cause little damage. However, if conditions permit, populations can become large. Symptoms of aphid activity include curling of leaves, yellowing, defoliation, reduction of growth, and, in extreme cases, branch dieback.

Control
    No control is recommended unless serious damage occurs. Then consult your local county extension agent for chemical controls.

CICADA,
MAGICICADA SP.

Description
    The periodical cicada is also known as the 13year (Magicicada tredecassini Alex. & Moore) or the 17-year (M. septendecim (L.)) locust, appearing in great numbers every 13 years in the South and every 17 years in the North. Periodical cicadas are widely distributed throughout eastern United States.

    Adult cicadas are large, dark, heavy-bodied insects with membranous wings and red eyes. The females possess a strong ovipositor. Adult cicadas can reach 1-1/2 inches in length. Nymphs live in the soil, feeding on plant roots, and so are rarely seen. Adult male cicadas produce a characteristic sound by vibrating their wings against their body.

Injury
    Injury to black walnut trees is caused by the adult female as she uses her ovipositor to make jagged slits in the bark and wood of twigs and small branches. Shredded wood fibers may be seen protruding from the slits. Affected twigs and branches are weakened and commonly break off in strong winds. Oviposition scars may be visible for several years after the injury was made.

Control
    No controls are recommended.

PLANT HOPPERS

Description
    Several species of plant hoppers have been found on black walnut, the most common of which are Anormenis septentrionalis (Spinola) and Metcalfa pruinosa (Say).

    The nymphs of both species are similar in color and size. They resemble small fluffy masses of cotton because of white waxy secretions they deposit around themselves and on the plant. Adults of Metcalfa pruinosa are dark blue-black in color, sometimes with a white,powdery substance obscuring the color. Anormenis septentrionalis adults are green to yellow-green. Both species are approximately 1/4 inch long and they hold their wings flat against the sides of their bodies. Plant hoppers are noted for their ability to jump when disturbed.

Injury
    Adults and nymphs are sucking insects, feeding on sap taken from leaves and stems of smaller twigs. Feeding damage is considered insignificant. The female adult, however, may cause the tips of small twigs to die when she deposits her eggs in zipper-like slits beneath the bark.

Control
    Control is usually not necessary.

2-MARKED TREEHOPPER,
ENCHENOPA BINOTATA (SAY)

Description
    The 2-marked treehopper is a small, darkbrown insect with two yellow spots on the center of its back. It has a thorn-like projection over the head and jumps when disturbed. Adults are approximately 1/4 inch long. The nymphs are black with white markings and often have spinelike structures extending from their abdomens. Treehoppers are widely distributed throughout eastern United States.

Injury
    Both adults and nymphs suck sap from walnut leaves. Often they can be seen feeding on the lower leaf surface or on the leaf rachis. Although they may be abundant within a plantation, their feeding habits do not appear to cause serious damage. However, female adults can damage twigs when they deposit eggs into small slits made by their ovipositors. After the eggs are laid the female covers them with a white frothy "plug" that later turns brown. After the eggs hatch, the slits remain evident as scars for several years. Treehoppers are present on walnut trees throughout the growing season.

Control
    Control is usually not necessary.

WALNUT LACE BUG,
CORYTHUCA JUGLANDIS (FITCH)

Description
    The walnut lace bug feeds almost exclusively on black walnut and is found throughout the range of black walnut.
    It is so named because of the adult's lacy wingcovers. The head is covered with a lace-like, arching hood. Adults are about 1/5 inch long and have transparent white wingcovers with dark bodies. The nymphs are much smaller, dark brown in color, and oval-shaped.

Injury
    Both adults and nymphs are found together on the lower surfaces of walnut leaflets where they suck the sap from the leaves. More than 100 nymphs and adults may be present at one time on one leaflet. Areas where they have fed are easily recognized because of cast skins, excrement, and dark, discolored patches of leaf. The upper leaf surface is stippled with tiny white spots that give the upper leaf surface a whitish appearance. Leaves of heavily infested trees may turn brown and fall off.
Control
    Consult your local service forester or county extension agent for the recommended control methods.