Mexican bean beetle (Epilachna varivestis), a member of the ladybug family, attacks many kinds of beans—bush, pole, and lima—as well as cowpeas and soybeans. Native to the Southwest and Mexico, it is now found throughout much of the United States. The oval adults are one-quarter to one-third inches long and yellowish brown to copper red. Each wing cover has eight small black spots arranged in three rows.
BIOLOGY: Adult beetles overwinter in weedy areas. They emerge over several weeks in mid- to late spring when air temperatures reach 50°F. After one to two weeks of feeding, females lay clusters of 40 to 60 yellow eggs on the undersides of leaves. These hatch in 5 to 14 days, and the larvae feed for two to five weeks. Larvae are yellow with rows of branched black-tipped spines on their backs. Mature larvae pupate on the underside of the leaves and adults emerge after 10 days. Two weeks later, they mate and the females begin laying eggs for another generation. In midsummer, the egg-to-adult cycle takes about a month. Typically only one generation occurs in the western and northern states, while up to four occur in the South.
SYMPTOMS: Larvae and adults feed on the undersides of the leaves and leave the upper surface, or epidermis, intact. This feeding injury, called windowpaning, causes the upper surface to dry up and fall out, resulting in a scorched, skeletonized leaf. Adults may also feed on young pods and stems.
CONTROL: Crush the eggs on the undersides of the leaves and handpick the adults and larvae, drowning them in a container of soapy water. Plant early-maturing varieties, because damaging numbers of beetles occur in mid- to late summer. Use row covers to exclude adults from emerging seedlings. After harvest, clean up or plow under plant debris to eliminate overwintering sites. Natural enemies of this pest include a parasitic wasp (Pediobius foveolatus) and predatory stink bugs, such as spined soldier bug (Podisus maculiventris). Insecticides may be warranted when defoliation exceeds 20 percent before flowering or 10 percent when pods are present. Use rotenone plus pyrethrin (Pyrellin), endosulfan (Thiodan), or carbaryl (Sevin).
From Horticulture Magazine