RWW adult on the leaf of a rice plant.

RWW feeding scars on a rice leaf. The presence of these scars indicates that adults have invaded the rice feeding and will probably begin laying eggs soon. It is important to apply controls for adults soon after application of permanent flood water to the field.

Mud ball are puparia that contain RWW larvae. Feeding by RWW larvae on roots of rice plants is what causes yield loss. Picture by J. Saichuk, LSU AgCenter.

Overview:

Rice water weevil (RWW) adults are grayish-brown weevils (1/8 inch long). Adults leave overwintering sites, invade rice fields and begin feeding on the leaves of rice plants. Females deposit eggs in the leaf sheath at or below the waterline. White larvae emerge from eggs in about one week and develop through four instars while feeding on the roots of rice plants. Larvae pupate in cocoons that are covered with a compact layer of mud and are attached to rice roots. The life cycle from egg to adult takes about one month.

Facts:

• Application of the permanent flood triggers females to lay eggs in rice leaf sheaths.
• Economic damage caused by larval root pruning reduces the number of tillers produced by the damaged plant.

What should you look for:

• Elongate feeding scars caused by adult feeding.
• Infested stands may be thin in appearance and contain yellow plants.

How you can manage rice water weevils:

• Avoid late planting of rice.
• Delay the application of permanent flood.
• Apply a pesticide to control rice water weevils at the correct time. Adults must be controlled before egg-laying occurs. Sample larvae by taking core samples.