AVRDC International Cooperators'
Fact Sheet

Sweet Potato Insect Pests
 

West Indian Sweetpotato Weevil
Euscepsis postfasciatus


Found in West Indies


Damage symptoms

There is internal tunneling in the root or stems. Root discoloration and a foul, terpene smell may be evident. A bitter taste may also be imparted.


Insect characteristics

Chewing mouthparts. Adults are reddish brown to grayish black with stiff erect hairs on their bodies. Their heads are elongated into a snout which at a glance, look like they have piercing-sucking mouthparts. Larvae are white, legless, and grublike with brown heads.


Where to look

The surface of the storage root may appear unblemished except for tiny sealed holes. Cut the roots open and look for the damage and the immature weevil. Adults are extremely difficult to find because of their secretive habits; they look like soil particles.


Technical information

Adults lay eggs singly and directly into the stem or root. The hole they make for insertion of the egg is plugged with fecal matter. Hatching larvae bore deeper and deeper into the root. When feeding is complete, the larvae pupate inside the root or stem and emergent adults tunnel out to complete their life cycle.

Internal damage
 
Surface damage
 

Larvae in stem


Control

Several steps are needed to control the weevil:

  • Uproot and burn all morning glory plants in the vicinity of the field.
  • Use clean cuttings. The ends (25-30 cm portions) of tender vines are normally used to plant a new crop. These distal tips are free of weevil eggs and larvae. However, older portions of vines may be infested. Never use tips longer than 30 cm to plant a new crop.
  • Soak cuttings in an insecticide solution. Follow the instructions on the label of the insecticide to prepare the solution. Soak cuttings for 5-10 minutes. Drain excess solution in the container. Use the same solution again and again to dip more cuttings. This is a very inexpensive and effective way of cleaning the cuttings of weevils. The insecticide treatment will also protect the crop in the field for up to one month from any new weevil infestation.
  • Regularly cultivate the soil to close cracks. Weevils travel through land cracks to gain access to storage roots and lay eggs. These cracks are caused by the underground storage roots becoming larger and larger. Land cracks may also be caused by lack of soil moisture, which is common in the dry season.
  • Grow sweet potato in a rotation (rice or sorghum are often used). This rotation will help break up the cycle of the weevil (and diseases, too). If you must plant sweet potato continuously, remove all debris and even small pieces of root from the previous crop.

Pheromone traps are useful in monitoring weevil populations, but this technology is expensive, not widely available, and not necessary.
 
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 conditions. 

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