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Extension Entomology

Walnut caterpillar

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Article author: Tyler Mays
Most recently reviewed by: Molly Keck & Wizzie Brown (2021)

Common Name(s): Walnut caterpillar

Description

The walnut caterpillar has a wide host range of woody plants and trees such as pecan, walnut, hickory (Ree and Jungman 2015). The larvae range in color from reddish brown as young larvae to black with grayish lines and hairs as mature larvae, and can reach lengths of up to two inches when fully grown. Damage caused by young larvae is typically localized to a few branches because the larvae feed in colonies. Later instar larvae can cause more damage as they spread throughout the canopy as they venture away from each other. Larvae damage the plant by feeding on leaves, eventually consuming the entire leaf surface and leaving only the main leaf vein and petiole.

Origin and Distribution

The walnut caterpillar is native to North America and is common throughout most of the eastern United States. The walnut caterpillar can be found as far west as Kansas, Minnesota, Oklahoma, and Texas. In Texas, the walnut caterpillar is found throughout areas east of the Pecos River (Knutson and Ree 2016).

Habitat & Hosts

The walnut caterpillar has a wide host range of both shrubs and trees. The primary host for walnut caterpillar include trees in the Juglandaceae family such as butternut, hickory, pecan, and walnut including black, English, Japanese and Persian (Ree and Jungman 2015).

Life Cycle

The walnut caterpillar is in the insect order Lepidoptera, and has a complete life cycle passing through egg, larval, and pupal stages before becoming an adult. In mid to late spring, overwintering pupae emerge as adult moths. After mating, adult females lay eggs once in a mass of around 600 eggs. Egg masses are laid in a single layer on the underside of leaves. Larvae hatch from eggs in roughly 9 days and pass through five larval stages (instars) over the course of about three weeks (Ree and Jungman 2015). During the first four larval stages, larvae are a reddish-brown color and can be found feeding in clusters. When molting from the fourth instar to the fifth instar, the caterpillars move to the trunk or a main branch and molt together. Larvae in the 5th instar are black with grayish markings and long hairs. Fifth instar larvae venture out to feed on their own. In Texas, the walnut caterpillar can complete 2 to 3 generations per year depending on the number of frost-free days (Knutson and Ree 2016).

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

In Texas, the walnut caterpillar rarely reaches levels that cause economic damage, but there have been occasional outbreaks that have caused economic loss (Knutson and Ree 2016). Typically parasitic insects, predatory insects, and arthropods like lady beetles and spiders keep populations from causing economic damage. Management of walnut caterpillars on small trees and in residential yards can be done by removing egg masses from leaves. Using insecticides to prevent economical damage on large trees and in orchards is more practical than physically removing egg masses. If you live in the state of Texas, contact your local County Agent or Entomologist for more management information. If you live outside of Texas, contact your local extension service for management options.

Related Publications

Walnut Caterpillar Factsheet https://citybugs.tamu.edu/files/2018/09/ENTO-041-Walnut-Caterpillar.pdf

Managing Insect and Mite Pests of Commercial Pecans in Texas. https://cdn-ext.agnet.tamu.edu/wp-content/uploads/2019/03/ENTO-048_-Managing-Insect-and-Mite-Pests-of-Commercial-Pecans-in-Texas.pdf

Citations

Knutson, A., and Ree, B. 2016. Managing Insect and Mite Pests of Commercial Pecans in Texas. Texas A&M AgriLife Ext. ENTO-048:1–28.

Ree, B., and Jungman, M. 2015. Walnut Caterpillar. Texas A&M AgriLife Ext. ENTO-041.

Bugwood Images

Blackmargined aphids (Pecan)

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Article author: Bill Ree
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Blackmargined Aphid

Pest Location

Vegetable and Fruit

Description

There are three species of foliage feeding aphids on pecan: the blackmargined aphid, Monellia caryella; yellow pecan aphid, Monelliopsis pecanis and black pecan aphid, Melanocallis caryaefoliae. Of these three, the blackmargined and yellow pecan aphid are also referred to a yellow aphids or honeydew aphids.

The winged adult blackmargined aphid can be identified by the wings being held in a horizontal position and by the black margins along the wing, Figure 1. The yellow pecan aphid, has clear wings which are held roof-like over the back of the body.

Habitat & Hosts

Blackmargined aphids can be found on pecan, Carya illinoensis (both improved cultivars and native trees) across the pecan belt. They are also found on water hickory, Carya aquatica.

Life Cycle

Blackmargined pecan aphids overwinter as eggs under the bark of trees. Nymphs emerge during the spring and feed primarily on the underside of the leaf on the primary and secondary leaf veins, Figure 2. During the summer, many generations of aphids are produced by unmated females giving birth to live female aphids. The time period from birth to adult is approximately 6 days and there can be 16 to 32 generations per year. All aphids during the growing season are females which give birth to live young. Males are not produced until the fall. Mature males mate with females and the females lay the overwintering eggs.

Both adults and nymphs feed on plant sap and excrete a sticky substance referred to as honeydew, Figure 3. A black sooty mold will grow in the honeydew which, if heavy enough, will reduce the photosynthetic ability of the foliage, Figure 4.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Primary management of blackmargined aphids is with insecticides. Management options with insecticides include the use of several active ingredients that are selective for aphids as well as other insects that feed on plant sap.

Other suggestions for aphid management include only treating problem varieties (if practical), treating only when insect densities exceed the treatment threshold of an average of 25 aphids per compound leaf, and rotating insecticides with different modes of action.

Other management options can include planting winter legume cover crops to generate populations of beneficial predatory insects such as lady beetles and lacewings during the spring. Also, using insecticides selective for Lepidoptera pests when treating for early season insects such as the pecan nut casebearer can help conserve existing populations of beneficial insects.

Two of the main beneficial insect groups which prey on pecan aphids are lacewing larvae (Figure 5) and lady beetle adults and larvae (Figures 6 and 7). Pecan aphids are also parasitized by a small wasp, Aphelinus perpallidus. Parasitized aphids turn black (Figure 8) and should not be mistaken for the black pecan aphid.

Bugwood Images

Southern green stink bug

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Most recently reviewed by: Tyler Mays (2018)

Common Name(s): Southern Green Stink Bug

Pest Location

Row Crop

Description

Adults are about 1/2 to 3/4-inch in length and are solid green. Immature stages vary in color from black for very small nymphs to green for larger nymphs. However, the immature stages have a distinctive pattern of whitish spots on the abdominal segments. Nymphal stages are often found together in high numbers because eggs are laid in clusters that appear as rows of small barrels on and around suitable food sources. Development from egg to adult requires about 35 days, but varies with temperature. Up to five generations per year may occur with greater numbers appearing in the fall before adults overwinter.

Habitat & Hosts

The southern green stink bug feeds on a wide variety of developing fruit, including cotton, peaches and tomatoes, and seeds such as pecan, sorghum and soybeans. They also feed on the parts of many ornamental and wild plants.

In fruit, such as tomatoes, damage is of two types. When the young green fruit is injured, the cells at the site of feeding are killed by the toxic saliva injected by the bugs into the plant. This area of the fruit stops expanding, while the cells around the dead cells continue to expand by increasing their water content. The result is deformed fruit that appears to have dimples. This type of damage has been called “cat facing.” When ripened or nearly ripened fruit is injured, the injection of toxic saliva merely kills a cluster of cells that later forms an off-color hard mass in the fruit, reducing fruit quality and producing a bad flavor to the fruit. Some plant diseases are spread by stink bug feeding.

Life Cycle

Simple metamorphosis adults deposit barrel-shaped eggs; immature stages develop through five stages or instars that appear similar to adults except that they do not have fully developed wings. Several generations can be produced each year.