beetle adults and larvae feed on the undersides of leaves of several
plants, including garden beans, cowpeas and soybeans, leaving the
leaves skeletonized with a lace-like appearance. Although feeding
occurs mainly on the leaves, young pods and even the stems may be
attacked and destroyed. Severely affected leaves often dry up and
drop off the plant, reducing photosynthetic efficiency and yield.
Serious infestations may result in the death of young plants.
bean beetle is one of the few harmful members of the lady beetle
family. The copper-colored adults resemble large lady beetles. They
are about 6 mm (1/4 inch) long and 5 mm (1/5 inch) wide, with 8
small black spots on each wing. Immature larvae are yellow and are
covered with large spines. Yellow eggs 1 mm (1/20 inch) in length
are laid in groups of 40-60 on the lower leaf surfaces.
bean beetle adults defoliating leaf
(R. A. Casagrande)
bean beetle larvae
(R. A. Casagrande)
overwinter on the ground in leaf litter and other sheltered areas
in fence rows and field edges. Adults begin emerging from these
protected areas when beans begin sprouting and continue to emerge
for up to two months. The adults feed for approximately two weeks
before depositing their eggs on the underside of leaves. Females
may deposit an egg-mass every two to three days. Eggs hatch in 5-24
days and larvae feed for two to five weeks before pupation. The
greatest amount of injury occurs in July and August, and the adults
begin to disappear in late summer.
- Plant early
and fast-maturing varieties to reduce damage and crop loss.
- Plant bush
beans instead of pole beans and pick pods as soon as they mature.
- Plants should
be plowed under as soon as the crop is harvested to eliminate late-developing
beetles and to prevent a within-field overwintering site.
covers such as Remay work well as protective barriers.
- If necessary,
plants may be protected by insecticides applied according to label
Richard A. Casagrande and David B. Wallace, 1999