Mexican Bean Beetle
Egg - The yellow egg is about 1.3 mm long and elliptical in shape.
Larva - The yellow larva is about 8.5 mm long and covered with dark, branched spines. Color plate.
Pupa - The yellow or copper colored pupa is about 6 mm long. It moves very little, has fewer spines than the larva, and is most commonly found on the lower half of the soybean plant.
Host Plants - The Mexican bean beetle feeds readily on many varieties of beans (bush, soybean, lima and pole) but may also infest other plants such as alfalfa, clover, cowpea, and kudzu.
Damage - On soybeans, larvae and adults feed between the veins on the surface of leaves, leaving a lacy network of the tougher leaf tissues. These remaining tissues die in about 2 days and turn brown. Fields seriously damaged by this beetle often have a brown or "burnt" cast.
Life History - Mexican bean beetles overwinter as both mated and unmated adults under litter and other rubbish in hedgerows, ditch banks, and woods. Emergence usually begins in March and increases until April or mid-May in most southeastern and mid-Atlantic states. After a feeding period of 7 to 10 days, females begin to lay groups of 40 to 60 eggs on the underside of leaves. Each female may lay an egg mass every 2 or 3 days, producing an average of 460 eggs. Oviposition by overwintering females lasts about 18 days. In spring, eggs hatch in 10 to 14 days, while in summer they hatch in 5 or 6 days. There are four larval instars which require about 35 days for development. Mature larvae transform into the pupal stage, which lasts from 7 to 20 days. New females begin laying eggs within 8 to 13 days after emergence. There are three generations per year in North Carolina.
