Bean Leaf Beetle
Adult - Though the adult varies greatly in color and markings, it is typically reddish-brown to yellowish with black margins and about 5 to 6 mm long. Each wing cover usually, but not always, is marked with three black spots. All bean leaf beetles, however, have a black, triangular-shaped spot on the forward margin of the wings.
Egg - The lemon-shaped egg is orange and about 0.85 mm long.
Larva - The larva is basically whitish with both ends colored dark brown. Conspicuously segmented, it has six tiny legs near the head. It grows to a length of about 10 mm.
Pupa - The pupa is soft-bodied, white, and about 5 mm long.
Host Plants - Hosts of the bean leaf beetle include bean, clover, corn, cowpea, soybean, peanut, and several leguminous weeds.
Damage - Damage to soybeans appears to be due primarily to the foliar-feeding adults. Bean leaf beetles prefer the youngest plant tissue available; when vegetative growth terminates, they will consume tender pod tissue. Pod damage is usually limited to the outer layers of the pod, the developing seeds being infrequently attacked. In North Carolina, damage is usually greatest in the eastern coastal counties from July through September though some seedling damage may occur on early planted soybeans. In addition to the beetles' direct attack, the adults are also known vectors of the bean pod mottle, cowpea mosaic, and southern bean mosaic viruses.
Life History - Adults overwinter in leaf litter or other vegetation, primarily in wooded areas. They become active in April and move to the earliest host plants available. In the southeastern United States, beetles do not usually attack soybeans until early May. They feed voraciously for several days and then mate. Each female lays 175 to 250 eggs in clusters of 12 to 24 in the soil at the plant's base. Eggs hatch in 1 to 3 weeks, depending upon the temperature. The larvae find their way to the base of the stem or roots and feed there for 3 to 6 weeks. Mature larvae form earthen cells within which the pupae form. In southern states, peak periods of adult activity generally occur the last of May, the last of July, the second and third weeks in August, and the second and third weeks of September. Second generation beetles overwinter in North Carolina.
