Mexican Bean Beetle
Description: The Mexican bean beetle (Epilachna varivestis) is one of the most destructive insect pests of beans in the eastern United States and portions of the southwest. Both the adult and the larval stages feed on the undersides of the leaves, and sometimes will attack young pods and stems. As a result of feeding, only the veins are left, giving the leaves a lacy appearance. Damage is most severe in July and August and occurs on all bean varieties, including bush, pole, lima, pinto, navy, kidney, soybeans and cowpeas. Bush varieties seem to be attacked more readily than pole varieties.
Adult beetles (1/4 inch long) are similar in appearance to large ladybugs. They are yellow to coppery-brown in color, oval in shape, and have 16 black spots on their wing covers. Larvae (1/3 inch long) are fat, hump-backed grubs with fuzz or spines, arranged in six longitudinal rows on their backs. They are orange to yellow in color and attach themselves to leaf surfaces.
Life Cycle: Adults overwinter in plant debris and other protected areas and emerge when the weather warms up in mid-to-late spring (usually when beans begin sprouting). After feeding for 1 to 2 weeks females begin to deposit yellow eggs in groups of 40 to 60 on the undersides of bean leaves. Larvae hatch in 5 to 14 days and feed for 2 to 5 weeks before pupating on the undersurfaces of leaves. Adults emerge 3 to 10 days later and live from 4 to 6 weeks. The period from egg to adult is about 30-70 days, depending on temperature. There are several generations each growing season.
Mexican Bean Beetle Control: Since damage is most severe during summer months, consider planting early maturing bean varieties to reduce pest problems. Hand pick the adults and immature stages from plants and drop them in a pail of soapy water. Also, remove the bright yellow eggs laid in clusters on the undersides of leaves. Floating row covers can be used as a physical barrier to keep beetles and grubs from damaging plants. Beneficial insects, such as ladybugs, lacewing and minute pirate bugs, are all voracious predators of both the egg and young larval stage. Apply diatomaceous earth to plants and/or spot treat with insecticidal soap to keep pest populations under control. Thorough coverage of both upper and lower leaves is necessary for control. If pest levels become intolerable, spot treat with botanical insecticides as a last resort. Treatments should be repeated in 7-10 days if additional beetles are found. Remove garden trash and other debris shortly after harvest to reduce over-wintering sites.