Plant Problem Diagnostic
Mexican Bean Beetle: How to Identify and Manage It
The short answer
The Mexican bean beetle looks like a large, coppery-brown ladybug with sixteen black spots, but unlike helpful lady beetles it eats bean foliage. Its bright yellow, spiny, oval larvae feed on the undersides of leaves, removing tissue between the veins and leaving a lacy, skeletonized look. The least-toxic controls are physical and biological: cover bean rows with row cover after planting, and crush egg clusters, larvae, and adults by hand.
The beneficial parasitic wasp Pediobius faveolatus can be released when larvae first appear, and destroying crop residue after harvest reduces overwintering numbers. Beans tolerate a fair amount of leaf loss before yield suffers, so treat based on real damage. If defoliation is severe or you cannot confirm the pest, contact your local Extension office before escalating.
How to identify Mexican bean beetle
Adults are 1/4 to 1/3 inch, convex, yellow to coppery-brown with sixteen black spots in three rows. Larvae are brilliant yellow, spiny, and oval, feeding on leaf undersides.
- Coppery beetle with black spots resembling a large ladybug
- Spiny yellow larvae on the undersides of bean leaves
- Skeletonized, lacy leaf tissue between the veins
Least-toxic management, in order
- 1Row covers — Cover bean rows after planting to exclude adults, leaving cover on where pollination is not required.
- 2Handpick and crush — Crush egg clusters, larvae, and adults by hand, focusing on leaf undersides.
- 3Release beneficial wasp — Release Pediobius faveolatus when larvae are first observed to parasitize them.
- 4Destroy residue — Mow or remove crop residue promptly after harvest to reduce overwintering beetles.
When to escalate
Bean plants can tolerate meaningful defoliation before yield drops, so escalate only when damage is heavy and handpicking cannot keep up. Contact your regional Extension office to confirm the pest and discuss least-toxic product options before treating.
✔ Don't kill the spotted beetle you find, check first: true lady beetles are beneficial predators, while Mexican bean beetles have spiny yellow larvae and eat foliage.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Maryland Extension — Mexican Bean Beetle on Vegetables — Adult and larval identification, skeletonizing damage, row cover, handpicking, and defoliation tolerance
- UMass Extension — Mexican Bean Beetle Biological Control — Release of the parasitic wasp Pediobius faveolatus when larvae first appear