Mexican Bean Beetle
Epilachna varivestis Mulsant, Coccinellidae, COLEOPTERA

DESCRIPTION

Adult - This copper red beetle is 6 to 8.5 mm long and dome shaped. Overwintering beetles are lighter in color. Each wing cover has eight small black spots that form three rows across the body when the wings are at rest.

Egg - The yellow egg is about 1.3 mm long and elliptical in shape.

Larva - The mature yellow larva is about 8.5 mm long and covered with dark, branched spines.

Pupa - The yellow- to copper-colored pupa is about 6 mm long. It moves very little and has fewer spines than the larva.

BIOLOGY

Distribution - Formerly, the Mexican bean beetle was limited from Colorado southward. It is now common throughout the U.S. with the exception of the Pacific Coast states.

Host Plants - Mexican bean beetles have a wide host range. They are most commonly encountered on garden and field beans as well as cowpea. Soybean, clover, alfalfa, and closely related weeds may also be attacked.

Damage - The Mexican bean beetle is the most injurious pest of beans (snap, lima, pole, kidney, pinto, navy, bush). If overwintering populations are high, seedling damage may occur, though economic damage usually does not occur before August. Both larvae and adults feed on leaves, leaving the upper surface intact. Damaged plants have a characteristic lace-like (skeletonized) appearance. These remaining tissues die in about 2 days and turn brown, often giving the entire field a "burnt" cast. Pods and stems are often attacked, and shredded plants may die before any crop is matured.

Life History - Adult beetles overwinter in hedgerows, ditchbanks, and woodlands and may attack plants soon after seedlings emerge in spring. Most beetles leave their winter quarters over a 2-month period. Following feeding, adult females deposit eggs in clusters of 40 or more on the undersurface of leaves. Eggs hatch in 5 to 14 days and larvae continue to feed for 2 to 5 weeks. Larvae pupate on leaves and adults emerge after about 10 days. Adults feed, mate, and lay eggs over a period of 2 weeks. Generation time from egg to adult is about 30 days. In North Carolina, there are three or four generations each year.

CONTROL

Snap bean varieties such as Wade, Logan, and Black Valentine are generally less severely damaged than other varieties by the Mexican bean beetle. Since damage is usually most severe during July and August, very early maturing bean varieties and fall plantings may be grown with little injury. Prompt removal of pods and destruction of old plants are suggested as insurance against population buildup. An extensive parasite release program is operational in the Delmarva Peninsula.

Chemical control consists of applying foliar insecticides to the undersides of leaves or using a granular insecticide in furrow at planting. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

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