Mexican Bean Beetle

Appearance

Adults are similar in appearance to other lady beetles, oval-shaped, approximately 6 to 7 millimeters long and bearing eight black spots on each elytron. Adult color is quite variable, ranging from bright red to rusty brown to golden yellow. The eggs are yellow, about 1.3 millimeters in length, and glued in clusters of up to 75 on the undersides of leaves. The larvae are usually yellow, spiny, and pill-shaped. Each is approximately 1.6 millimeters in length when first emerged, and grows to about centimeter length before pupation.

Distribution

Mexican bean beetle is present in the United States and found in most eastern states of the United States and Mexico. It can be found as far south as Guatemala and north into southern Canada or New England. The Mexican bean beetle is likely native to the southern plateau region of Mexico. Presence depends on the factors such as precipitation.
It does not cause significant crop damage in Guatemala and Mexico, but can be abundant in isolated areas of the western United States.

Behavior

Adults emerge from dormancy in late spring, and each female lays several hundred eggs in clusters of 50 to 75 on bean plant leaves. The larvae are voracious feeders, and can inflict heavy damage on a field of bean plants during an infestation. After a few weeks of feeding, the larvae pupate in groups under the leaves. They winter as adults, and often travel long distances to find new fields.

Food

Both adults and larvae feed on leaf, flower, or pod tissue on beans and other legumes. They can be found on a great variety of bean and crop plants, including green bean, thicket bean, lima bean, cowpeas, adzuki bean, mung bean, and soybean. It will also attack other legumes, including some ornamentals, such as Chinese wisteria and lupines. Adult beetles may eat the fruits and flowers of the plants, but generally prefer the leaves. Feeding damage is most prevalent from skeletonization where beetles feed on the parenchyma of the leaves from the underside, leaving the upper epidermis intact. This gives the leaf a lacy appearance. The larvae generally do much more damage than the adults.