Bean Leaf Beetle

• Latin name is Ceratoma trifurcata
• Although the larvae feed on soybean roots, most damage occurs from adult feeding on foliage or pods
• Found east of the Rocky Mountains, wherever soybeans are grown
• No significant natural enemies are known
• Hosts: alfalfa, clover, green beans, wild legumes such as tick trefoil
• Generations per year
  • 3 – Southeast United States
  • 2 – Iowa and Illinois
  • 1 to 2 – Wisconsin
  • 1 – Canada
• Adults overwinter in woodlots and fence rows
• Quickly killed if exposed to temps below 14° F
• Adults may feed on alfalfa in spring before soybeans emerge

Crop Symptoms

• Impact from larvae is unknown, but thought to be insignificant
• Leaf feeding from adults causes little impact unless defoliation exceeds 25%
• Pod feeding results in greatest damage and affects both quality and yield
• Adults also transmit bean pod mottle virus, which:
  • Reduces soybean yield
  • Reduces soybean quality
  • Causes green stem and delays harvest
    
    

Crop Symptom Pictures

Leaf Injury

Area of green stem

Pest ID

Adult:

• Bean leaf beetle adults are 1/5 inch long
• Color is typically dark yellow, but may be orange or red
• Wing covers often with four “rectangular” marks, but may have two or no marks
• Best identifying mark—black triangle behind pronotum (neck region)
  
  

Larvae:

• Found in soil near roots and resemble corn rootworm larvae
• Body color is white and head color is dark brown/black
• Often found feeding in nodule

Management Considerations

Resistance

• Neither native nor transgenic resistance are currently available for bean leaf beetle
  
  

Beneficial Insects (Natural Enemies)

• Very little impact documented
• Not a recognized deterrent to beetle populations
  
  

Planting

• If the field has a history of bean leaf beetle injury or bean pod mottle/green stem, consider planting slightly later after most bean leaf beetle adults have moved away from
  the area

Scouting Practices

Early Pod Fill Stages: R1-R3 

• If defoliation approaches 20 to 25% and large numbers of BLB adults are present, consider insecticide application, especially if beetles exceed 20 per 20 sweeps of a sweep net
• Decision should be based on increasing or decreasing beetle numbers, costs of control and grain price of soybeans

Late Pod Fill Stages: R5-R7  

• If pod injury is above 10% and beetles exceed 3 per sweep, consider insecticide application, especially if other pod feeding insects (grasshoppers) are present
  • Value of control will depend on continuing injury and pod maturity