**Mexican Bean Beetles** (*Epilachna varivestis*) are a species of Lady Beetle (family Coccinellidae) that is a severe, widespread **agricultural pest**, unlike most of their beneficial relatives. Both the adult beetles and the larvae feed exclusively on plants in the legume family (*Fabaceae*), causing devastating damage to **beans** (snap, lima, soy), cowpeas, and occasionally alfalfa. Their feeding behavior, known as **skeletonization**, involves consuming the soft tissue of the leaves from the underside, leaving behind a lace-like network of veins and causing the leaves to dry up and die.
Taxonomy and Classification
Mexican Bean Beetles belong to the order Coleoptera (Leaf Beetles, Chrysomelidae). They undergo complete metamorphosis. They are one of the few species in the family Coccinellidae that are herbivorous pests, rather than predators. This species is native to Mexico but has spread widely throughout North and Central America.
Physical Description
Adult Mexican Bean Beetles are 1/4 to 3/8 inch long.
- **Adult (Key ID):** Yellowish-copper to orange-brown, oval, dome-shaped beetle, with **sixteen distinct black spots** arranged in three rows across the back (elytra).
- **Larvae (Key ID):** Yellowish, oval, soft-bodied, and covered in dense, dark, branching **spines** (dendrites), making them look spiky or fuzzy.
- **Damage Sign (Key ID):** Leaves are severely **skeletonized**—only the veins remain, and the leaves have a characteristic lace-like appearance. The feeding occurs almost entirely on the **underside** of the leaf.
- **Conflict:** Severe crop loss in legumes.
Distribution and Habitat
Mexican Bean Beetles are prevalent across the eastern U.S. and parts of the West. Their habitat is specifically the foliage of bean plants (garden or agricultural field). They overwinter as adults in leaf litter near previous host fields.
Behavior and Conflict
The conflict is rapid and severe defoliation of bean crops.
- **Dual Damage:** Both the adults and larvae feed on the foliage, with the larvae being the more destructive stage.
- **Under-Leaf Feeding:** Because they feed and lay eggs almost exclusively on the underside of the leaves, they are often difficult to spot and are protected from overhead contact sprays.
- **Multiple Generations:** They can have multiple generations per year, leading to continuous pest pressure from mid-summer until fall.
Management and Prevention
Control is integrated pest management (IPM), requiring crop rotation and targeted sprays.
- **Crop Rotation:** Plant beans as far as possible from the previous year’s infested plots to deter overwintered adults.
- **Sanitation:** Plow under or remove all crop residue immediately after harvest to destroy overwintering sites.
- Plant early-maturing varieties to escape peak infestation.
- In small gardens, hand-pick and destroy the adults, larvae, and egg masses (bright yellow clusters found on the underside of leaves).
- Apply insecticides, ensuring the spray reaches the **underside of the leaves** where the insects feed. Use insecticides derived from Neem or products containing carbaryl or pyrethroids.
Conservation and Research
Mexican Bean Beetles are managed as key agricultural pests. Research focuses on breeding bean varieties with natural resistance to the beetles, and optimizing the use of the introduced biological control agent, the parasitic wasp (*Pediobius foveolatus*).