Soybean leaf beetles

Another pest of potential concern is the bean leaf beetle. Adults of the bean leaf beetle are a concern on emerging soybeans, where the leaf feeding and potential to spread viral diseases are a concern, but these pests can also be a concern now at the reproductive stages.

This beetle is native to North America and was first described as a pest of edible beans when the continent was first colonized. As soybean production increased, the bean leaf beetle adapted to feeding on soybean foliage and pods. Bean leaf beetle adults are about 1/4 inch (6 mm) long and usually yellow, tan, or red in color. The beetle is distinguished by a distinct black triangular mark on its wing covers directly behind the thorax (the "neck" area of the insect). Often two black spots are present on each wing cover and a distinct black band extends around the outer edges. Sometimes the wing covers have no markings, except for the black triangle. When disturbed, the bean leaf beetle typically folds its legs and falls to the ground where it may remain motionless for some time.

First and second-generation beetles chew small round holes in soybean leaves during mid and late season. Once the maturing foliage becomes less attractive to beetles, they feed on the green tissue of pods, leaving a thin membrane over the seed. During pod maturation, this membrane often cracks leaving an entry hole for air borne plant pathogens. These pathogens may cause discolored, moldy, shriveled, and/or diseased beans.

Scouting for pod damage: Randomly select 2 plants in each of 5 areas of the field and count the number of pods per plant and the number that show insect damage (10 total plants). Figure the percentage of damaged pods per plant for the field as a whole. Note pod maturity, as earlier feeding leads to more potential damage. Also determine the number of beetles per sweep using an insect sweep net. Take 5 sets of 20 sweeps in the field. Determine the number of bean leaf beetles per sweep. Thresholds for control are based on potential loss, price of soybean and cost of treatment. Refer to online resources from universities for threshold charts.

Bean Leaf Beetle pod feeding:
  

Leaf feeding.:

Photos by Brad Ruden