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Insect Quiz July, 2004

August Quiz 2004

You are walking in your yard and are startled to find your sumac covered with red and yellow striped caterpillars. These insects are almost two inches long and have eaten about half the leaves on your shrubs. You notice that when you get close to the sumac, many of the caterpillars rear their bodies into a very threatening posture.

QUESTIONS

1. What are these insects?

These caterpillars are yellownecked caterpillars, Datana ministra. The larvae have black heads and striped bodies with fine white hairs. Yellownecked caterpillars get their name from the orange yellow rectangular spot behind their heads. They have two color phases, orange yellow with red orange stripes and black with orange yellow stripes. Adult moths lay eggs in June and July and the caterpillars feed from mid to late summer.

2. Are they harming the sumac?

Yellownecked caterpillars feed on a wide variety of trees and shrubs, including oak, birch, elm, maple, crab apple, walnut, mountain ash, honeylocust, and sumac. Fortunately, even when these caterpillars are numerous, healthy, well-established trees and shrubs can tolerate their feeding in most cases. In cases when woody plants have been recently transplanted or are unhealthy, then the extra stress of heavy defoliation could damage trees and shrubs.

3. Are they harmful to people?

These caterpillars are gregarious, i.e. they feed together in nonsocial groups on branches. When the are disturbed, yellownecked caterpillars will arch their heads and the tip of their abdomens, forming a ÎU'. They try to appear threatening, particularly to ward off natural enemies, such as fly and wasp parasites. But they are quite harmless to people.

4. What is the best management?

In most cases, you can ignore yellownecked caterpillars. Trees and shrubs can easily tolerate their defoliation. This is especially true as the caterpillars approach two inches in length, their full grown size. Once they are this big, they are nearly done feeding. If you have had an ongoing problem with yellownecked caterpillars and need to treat them, monitor woody plants in July and treat the caterpillars soon after they hatch and are still small. There are many insecticides that are effective. Examples of less toxic products include Bacillus thuringiensis or insecticidal soap.



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