AVRDC
Crop Protection Guides

Sweet Potato Insect Pests
 

Sweetpotato Weevils
(Cylas formicarius (throughout tropics) and
C. puncticollis (Africa)

In This Guide
Damage symptoms 
Insect characteristics 
Where to look 
Technical information 
Control 
Damage symptoms

Small and scattered feeding holes are occasionally present on the leaves. The surface of the storage roots are scarred or chewed. Internal portions of the roots are tunnelled out and some areas maybe soft. Rotting may occur and a strong terpene smell may be evident. 		  

 

Larva feeding on top of tomato
Insect characteristics

Chewing mouthparts. Adults are brown to black with heads elongated into a snout. They appear to have typical piercing-sucking mouthparts but don't. Larvae are white with brown heads. They are fat, grublike and legless.		  

 

Larva feeding inside the fruit
Where to look

Adults are commonly found on the foliage, bu they quickly drop to the ground if disturbed. Select storage roots that appear soft, smell, or have external scarring or small darkened holes. Cut these open and look for tunneling and grublike larvae.
Technical information

Continual generations can occur even in temporary storage conditions. Female weevils lay eggs singly in the stem or storage root. These insects pupate in the stem or root. Infested sweet poato develops a bitter taste and is not marketable. No alternative hosts outside the morning glory famiy have been reported for the pest.		  

Healthy fruitworm egg
 

Healthy fruitworm egg
   

Control

Monitor the pest by selecting a leaf from 30 random tomato plants. Choose leaves located below the highest open flower. Healthy eggs are white with a reddish ring. If more than five healthy eggs appear, begin treatments. Pesticide treatments are also required when large numbers of small caterpillars are found feeding on leaves.

This pest has developed resistance to many insecticides. Select an effective chemical. The following insecticides are often used for control: esfenvalerate (Asana), methomyl (Lannate), Bacillus thuringiensis, azinphosmethyl (Guthion), carbaryl (Sevin), and Pyrethrin/Rotenone.

Parasitic wasps, especially Trichograma spp., are important natural enemies. Fruitworm eggs turn black when parasitized.

Avoid planting tomato near corn or cotton to prevent heavy pest infestations.
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 to internet version. 

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