Common Name: Mexican Bean Beetle
Scientific Name: Order Coleoptera, family Coccinellidae, Epilachna varivestis, also Cerotama spp.
Size: Adult 1/4"
Identification: Adult beetles are oval, yellowish brown or copper-colored, with sixteen black spots arranged in rows across the wing covers. They look just like fat lady beetles. Larvae are fat yellow grubs with no legs but spines from each segment. Eggs are yellow ovals.
Biology and Life Cycle: Adults overwinter in organic matter. They emerge in spring to feed for a while; females lay eggs on end in clusters of forty to sixty on the underside of bean leaves. Eggs hatch in five to fourteen days, larvae feed for two to five weeks, pupae are attracted to lower sides of leaves, adults emerge in a week. New adults are solid yellow at first, later darken and become spotted. Several generations a year.
Habitat: Most abundant in weedless fields and in the bean garden.
Feeding Habits: Adults and larvae feed on the undersides of leaves, causing a skeletonizing effect.
Economic Importance: Will destroy bean crops.
Natural Control: Plant a biodiverse garden and use lots of flowers. Release spined soldier bugs, parasitic wasps, and assassin bugs.
Organic Control: Plant cover crops or mulch bare soil. Cover young plants with floating row cover. Soybeans can be planted as a trap crop to be destroyed when infested. Crush egg masses daily. Spray plant oil product, garlic-pepper tea, neem or Liquid Fire Ant Control formula.
Insight: Neither of us has ever seen a serious infestation of this insect in Texas. This beetle is troublesome in the Northeast, skips Texas for some reason, then goes on down into Mexico and causes more trouble. Because most insect books mention it and its romantic name is easy to remember, people falsely identify other beetles as the Mexican bean beetle and end up unnecessarily using pesticides.