Insect Note #29 (Revised)

Prepared by:
K. A. Sorensen, Extension Entomologist

Dated 5/94
Placed on the Web 4/95 by the Department of Entomology, NCSU

The Cowpea Curculio

Chalcodermus aeneus Boheman, Coleoptera: Curculionidae

The cowpea curculio or cowpea pod weevil is a native insect pest of southern peas and beans in the South. This weevil also feeds on cotton and strawberries. Though most widely recognized as a problem in the home garden, it also causes serious damage to commercial plantings as well.

Description of Injury

One first observes small, brown, blister-like spots on harvested pods. Small, pale yellow, legless grubs are frequently found within the damaged peas or beans.

Life History

Cowpea curculio adult pass the winter in crop refuse or weeds around previously infested plants. Black, humpbacked adults leave their overwintering sites in April through July. The adults are long lived. Adult weevils puncture developing pods with their snout. They lay an egg in each hole that hatches into a brown- headed, legless grub which feeds on peas or beans. When full grown, the grub chews full grown, the grub chews an exit hole through the pod and drops to the ground where it changes into an adult. Most grubs leave the pod within 7 days. However, some 21 days are required to complete the life cycle. There are 2 generations each year. However, eggs are laid over an extended period and generations overlap. Hence, all stages may be found at the same time.

Management

Late peas or beans isolated from earlier plantings are usually not as severely damaged. Damage is less during periods of hot, dry weather. Ants and a tachnid parasite feed on cowpea curculios but do not bring about complete control. Crop rotation and sanitation are valuable in controlling this pest.

For chemical control of the cowpea curculio, an insecticide should be applied when first blooms appear and repeated at 5-day intervals as needed. Endosulfan (Thiodan/Phaser) 50WP at 2 pounds of formulation per acre or 2 tablespoons in a gallon of water are suggested. Endosulfan has a 3 day time limitation until harvest. Do not make more than 3 applications of endolsufan per season.

Cowpea curculio adult and larva -- Adults are black humpgacked weevils 6 to 7 mm long. Larvae are pale yellow and have brown heads. Larvae are legless and graw 6 to 7 mm long. Curculios leave feeding scars -- small holes in pods and peas; larvae feed inside green seeds.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsements by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. All pesticide recommendations provided in this publication apply to pest control in North Carolina. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain information about product usage in your locale and examine a current product label before applying any chemical. The information presented on pest biology is based on conditions in North Carolina and may not be applicable to your locale. For further information, we recommend that you contact the Cooperative Extension Service office in your county.