AVRDC International Cooperators'
Fact Sheet

Tomato Insect Pests
 

Beet Armyworm
Spodoptera exigua 


Found in North America and Southeast Asia

 damage to leaves


Damage Symptoms

Feeding scars on the fruit surface are shallow and dry. The inside of the fruit is often hollowed out. This cavity is usually dry and may have frass and decay.


Insect Characteristics

Chewing mouthparts. Caterpillars are dull green with many light stripes along their backs and a broader stripe down each side. The undersides are usually yellow. Adult moths are grayish and active at night.


Where To Look

Caterpillars are commonly found in two places. Groups of newly hatched larvae can skeletonize tomato leaves and typically feed under a webbing of silk. Look for the webbing of the feeding damage. Older caterpillars become more independent and can be found gouging the surface of the green fruit.		  
external fruit damage
External fruit damage
larva entering a stem
Larva entering a stem
     

Technical Information

Populations develop continually throughout the year. Adult moths lay their eggs in off-white scale-covered clusters on the leaves. When feeding is complete caterpillars pupate in the soil. The population can develop on some weeds. This pest also commonly feeds on onion, soybean, chili pepper, and sugar beets.


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: 2001. 
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. Pesticide and other control recommendations should be adapted to local situations.
 

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