Beet armyworm on onion

AVRDC
Crop Protection Guides

*Onion Family Insect Pests* Beet armyworm Spodoptera exigua	In This Guide
	Damage symptoms
	Insect characteristics
	Where to look
	Technical information
	Control

Damage symptoms Leaves are partially or completely consumed. Holes or crescent-shaped areas in leaves are removed.
		Damage

Insect characteristics Chewing mouthparts. Armyworms, as the common name implies, feed in groups. Caterpillars are dull green with many light stripes along their backs and a broader stripe down each of their sides. Their undersides are usually yellow. Adult moths are grayish and can only be seen flying after dark.
		Larva on onion leaf

Where to look

Feeding immatures will not be hidden, but are easily seen in groups on leaf surfaces. Sometimes, larvae bore into tubular leaves and feed concealed inside. If feeding holes are small, then look carefully at the leaves. The insects, in their early stages of development, are small (about 5 mm long). Usually, you will find armyworms where insect frass and new feeding damage can be seen.

Technical information Populations may develop continually throughout the year. Adult moths lay their eggs in white to dull-white hair-covered clusters on the leaves. When feeding is complete caterpillars pupate in the soil. Populations can develop on some weed species. Beet armyworm also feeds on tomato, soybean, groundnut, sugar beet, and crucifers.
		Larva on the surface of the soil

Control

Spraying of chemical insecticides has been the major approach to combating armyworm. But the pest is developing resistance to many chemicals. In response, farmers sometimes mix several insecticides together in hope that one of them will be effective. These strategies are not sustainable.

The use of alternative, biological control measures are very useful. Parasitic wasps and nuclear polyhedrosis viruses (NPVs) that target armyworm are commercially available. Strains of Bacillus thuringiensis (Bt) are useful for killing armyworm larvae.

Pheromones for armyworm are commercially available. They are useful for monitoring, and especially to determine the entry of the pest into the field. Pheromones by themselves will not control beet armyworm. They need to be accompanied by chemical or biological control measures.

Last updated: July 2000.
Information from: Field Guide: Insect Pests of Selected Vegetables in Tropical and Subtropical Asia. 1995. B.L. Parker, N.S. Talekar and M. Skinner. Publication 94-427. Pest control recommendations added.

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