SP 341-Z Mexican Bean Beetle Insects (Available online only)

Mulsant, is the most injurious insect pest of beans. The adults are 1/4 to 1/3 long, slightly oval and yellow-ish with 16 black spots on their wing covers (elytra). The adults look like large ladybird beetles and are classified in the ladybird beetle family, Coccinellidae. While the Mexican bean beetle and the closely related squash beetle feed on plants, other ladybird beetle spe-cies prey on insects and mites. Life History The adult Mexican bean beetle overwinters under leaves or other debris in grassy, weedy areas and around fence rows or trees. The adults move into the bean fields and gardens soon after the bean plants emerge. The adults feed for a week or two before laying their yellow egg masses on the underside of the leaves. The eggs hatch in five to 14 days. The bright yellow larvae are oval-shaped with six rows of branched spines. The larvae feed for two to five weeks. Larvae and adults feed on all types of beans and are an occasional pest of soybeans. They generally feed on the underside of leaves, removing all of the leaf tissue except the clear layer on the upper side of the leaf, called the epidermis. This damage, called “window-paning, ” gives the leaves a lacelike or skeletonized ap-pearance. The remaining leaf tissue turns brown in a couple of days, giving the field a burnt cast. New pods and stems are often attacked, and severely damaged plants may die prematurely. Control Early-maturing bean varieties and fall plantings allow crops to escape most of the serious Mexican bean beetle damage occurring in July and August. Destroying old plants and removing pods promptly will aid in slowing the buildup of Mexican bean beetle populations. Treatment is needed if populations of Mexican bean beetle