Departments of Plant Pathology and Entomology
North Carolina Cooperative Extension Service
North Carolina State University

Photograph of Flower Beds at NCSU Arboretum ORNAMENTALS

North Carolina Pest News
Volume 11, Number 19, August 23, 1996
Stephen J. Toth, Jr. and Thomas A. Melton, editors

The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.

From: James R. Baker and Stephen B. Bambara, Extension Entomologists

European Corn Borers on Ornamental Plants

Each year European corn borers are reported tunneling in the stems of garden or fall mums. One borer per pot is enough to ruin the economic value of the entire pot, because the infested stem falls over and spoils the symmetry of the pot. Although best known as a pest of chrysanthemums, the European corn borer has been found boring into more than 200 different plants, including asters, cosmos, dahlia, daisies, gladioli, hollyhocks, roses, zinnia, and vegetable and field crops. The adult is a yellowish-brown stout moth. Females lay up to 400 eggs in flat masses on the underside of leaves of the host plant. The eggs resemble tiny fish scales in shape and arrangement. The caterpillars hatch and feed on the surface of leaves for a few days. As the borers mature, they bore into the stalk of the host plant to feed. The larvae push frass from the stem which collects at the opening. European corn borer caterpillars are cannibalistic, explaining why only one or two borers are found per pot even though the moth laid dozens of eggs. This pest overwinters in the stalk, so destroying the stalks of corn, dahlia, mums and weeds in the area should help to suppress next season's population; however, it is not guaranteed since the moths fly readily. It is best to spray garden mums with a pyrethroid such as Talstar, Mavrik, or Tempo 2 every two or three weeks from mid-August on. After the borers are in the stalk it is essentially too late, although a desperation spray of Dursban (DuraGuard) could be attempted. Additional information on the biology of the European corn borer is provided in North Carolina Cooperative Extension publication AG-136, Insect and Related Pests of Flowers.

Stinging Caterpillars

Stinging caterpillars have sharp hairs on the body that contain an urticating liquid which causes a sudden, painful burning sensation on the skin of the individual who is unfortunate enough to brush against the caterpillar (the stings are as uncomfortable as the stings of the Portuguese Man-of-War or wasps). The acute pain may last several hours. Swelling associated with the sting may be evident for several days. Some persons are very sensitive and may require professional medical treatment. Sevin, Orthene or one of the Bacillus thuringiensis (B.t.) pesticides should give adequate control, although B.t. is not very effective on older caterpillars. At least three families of caterpillars have species that can sting. These are giant silkworm moths (io moth and buck moth), flannel moths (hackberry leafslug and puss caterpillar), and slug caterpillars (saddleback, spiny oakslug, stinging rose caterpillar).

Giant Silkworms Moths

Io moth caterpillars feed on all sorts of trees, shrubs and vegetables. Even though the caterpillars sometimes feed in groups and move in trains from place to place, they are rarely abundant enough to be considered pests. They are of interest only because they sting and because of their relatively large, spiny appearance. The mature larvae spin thin, paper-like cocoons of brown silk in which to pupate. The winter is spent in the cocoon as a pupa. The following summer adult moths emerge to mate and lay eggs. Adults are beautiful bright yellow to reddish-brown moths with large eyespots on the hind wings. It must have been the beauty of this moth that led to its common name, Io. Io was the Greek goddess who was so beautiful that she was changed into a heifer and ultimately banished to Egypt once she regained her human form.

Buck moths are so named because they fly during the day during deer season (it is unusual for most moths to fly during the day). This species differs from the others in the family of the giant silkworms because the female moths lay their eggs in the fall for next year's brood of caterpillars. The eggs are laid in dense clusters around twigs. When buck moth caterpillars mature, they burrow into the soil rather than spinning a cocoon! Most of the moths emerge in the fall although some may not emerge until the following year. The other species of giant silkworm moths emerge in spring and summer and lay eggs from which caterpillars hatch in only a few days.

Flannel Moths

The hackberry leafslug is one of the stinging caterpillars most often associated with redbud in North Carolina. The moth is pure white and apparently emerges sometime during the summer to lay eggs on hackberry, redbud, beech or mimosa. The larvae feed in groups at first, but then branch out on their own. When mature, the caterpillars crawl to the ground and pupate in a cocoon just below the soil surface. Although this is one of the more common pests of redbud, in any one location the hackberry leafslug can be relatively rare except for occasional outbreak. Insect populations are notoriously variable.

Puss caterpillars are called puss caterpillars because with their thick, fluffy setae they resemble headless, legless pussy cats. The adult is a attractive yellowish-brown moth with fluffy wings appropriately called a flannel moth. Puss caterpillars feed on various deciduous trees and shrubs, especially oak, elm, hackberry, maple, and sycamore. The young larvae sometimes feed in groups on the surface of the leaf. Older larvae devour the entire leaf. The caterpillars finally spin a dense cocoon in which it spends the winter. Puss caterpillars are usually not abundant enough to be noticed, although rare outbreaks may be widespread and may cause severe defoliation. There may be two generations a year, and the winter is spent in the cocoon spun some place on the host tree.

Slug Caterpillars

Saddleback caterpillars have a brown saddle-shaped spot on the middle of their green backs. These larvae are called slug caterpillars because the prolegs lack tiny hooks that most other caterpillars have, and the prolegs are so short that some of the slug caterpillars resemble slugs. Saddleback caterpillars overwinter in tough silk cocoons with the urticating hairs imbedded (even the cocoons sting!). Dark, reddish-brown moths emerge the following spring and summer and lay flat eggs on leaves of various trees, shrubs and other ornamentals, and corn. There is one brood per year.

The spiny oakslug, Eudea delphinii, feeds on oak, pear, willow, wild cherry and other trees. It is found throughout eastern mixed deciduous forest areas. The moths are a mottled dark brown with a noticeable pale green spot near the base of each forewing and often with a second, smaller green spot near the tip. The moths have been collected from May through September in North Carolina.

The stinging rose caterpillar, Parasa indetermina, is also one of the slug caterpillars. These are called slug caterpillars because the prolegs lack tiny hooks that most other caterpillars have, and the prolegs are so short that some of the slug caterpillars resemble slugs. Stinging rose caterpillars overwinter as pupae in tough cocoons on the ground. Pale cinnamon brown moths with green and brown markings emerge the following spring and summer and lay flat eggs on the leaves of various trees and shrubs. On roses, stinging rose caterpillars feed on the lower surfaces of leaves.

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