Mexican bean beetle
The Mexican bean beetle is the only member of the ladybeetle family (Coccinellidae) that is a serious plant pest rather than a beneficial predator -- a useful thing to remember when you see a yellow-and-black spotted beetle on your beans and assume it is eating pests. It is the pest. The.
—- title: "Mexican bean beetle" slug: mexican-bean-beetle hub: problems category: "Disease-by-host" description: "The Mexican bean beetle is the most damaging insect defoliator of beans in the eastern US. Identify the skeletonized leaves and yellow larvae, understand the multi-generation life cycle, and manage with targeted insecticides and natural enemies." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-
The Mexican bean beetle is the only member of the ladybeetle family (Coccinellidae) that is a serious plant pest rather than a beneficial predator — a useful thing to remember when you see a yellow-and-black spotted beetle on your beans and assume it is eating pests. It is the pest. The skeletonized, lacy appearance of beans after Mexican bean beetle feeding is one of the most severe forms of foliar damage in the vegetable garden.
I don't grow beans at my Long Island property, so this guide draws on Penn State Extension, Cornell Cooperative Extension, and Clemson HGIC research.
The pest
The Mexican bean beetle (Epilachna varivestis) is in the family Coccinellidae, the same family as ladybeetles. Per Penn State Extension, adults are:
- 6–7mm diameter, oval, convex
- Yellowish-brown to copper-colored with 16 black spots arranged in three rows
- Similar in appearance to beneficial ladybeetles but copper-colored with more spots (beneficial ladybeetles are typically bright red or orange with fewer spots, most commonly 7)
The species is native to Mexico and Central America and spread through the eastern US, where it is now a common pest in most states east of the Mississippi.
Identification
Adults
Per Clemson HGIC:
- 6–7mm, rounded oval, copper-yellow to tan with 16 black spots
- Feed on the underside of bean leaves, consuming the leaf tissue between veins but leaving the upper cuticle intact — this produces the characteristic "skeletonized" or "window-pane" leaf appearance
- Found on the undersides of leaves
Eggs
Per Cornell Cooperative Extension, egg clusters are:
- Bright yellow-orange, oval, 1.2mm
- Laid in clusters of 40–75 eggs on the underside of leaves
- Distinguishable from squash bug eggs by color (brighter yellow), shape (more oval), and host (beans not cucurbits)
Larvae
Per Penn State Extension, larvae are:
- Bright yellow-orange, 8–9mm at maturity
- Covered with branched, soft spines (unlike many spiny caterpillars, the spines do not sting)
- Found in groups on the leaf underside; feed gregariously in early instars, dispersing as they mature
- The larval stage does the majority of the foliar damage
Damage
Per Clemson HGIC, feeding damage produces:
- Skeletonized leaves — the entire leaf area is consumed except for the upper cuticle and major veins; the leaf appears as a transparent, papery skeleton
- Severe infestations can strip an entire bean planting
- Pods and stems are also fed upon in heavy infestations, reducing yield directly
Life cycle
Per Penn State Extension:
- Overwintering: Adults overwinter in leaf litter in and around bean fields; emerge in spring as temperatures exceed 60°F (16°C)
- First generation: Adults lay eggs in June; larvae feed July; first generation adults emerge late July–early August
- Second generation: Second generation adults lay eggs August–September; second generation larvae are often the most damaging because populations accumulate over the season
- In the mid-Atlantic and Northeast, one complete generation and a partial second generation occurs per year; farther south, two complete generations are typical
The peak damage period is July–September in most of the northeastern US.
Management
Inspect and remove egg masses
Per Cornell Cooperative Extension, inspecting bean leaf undersides weekly from mid-June onward and removing egg clusters before hatching is the most labor-efficient management approach. Crush egg clusters or remove affected leaves. This interrupts the second generation when populations would otherwise build highest.
Early planting
Per Penn State Extension, planting beans early (as soon as soil is workable) allows harvest before peak second-generation populations in August. Early-planted snap beans can often complete their productive season before damage becomes severe. Late-planted or succession-planted beans face the full force of August populations.
floating row cover
Per Clemson HGIC, row cover excludes adults from egg-laying during the first generation. Remove at bloom to allow pollinator access; replanting a fresh bed under cover may provide additional late-season production with reduced beetle pressure.
Spinosad
Per Penn State Extension, spinosad is effective against larvae and has low impact on most beneficial insects. Apply every 7–10 days when larvae are present. Begin applications when first-instar larvae (small, gregarious) are detected on leaf undersides, before they disperse and grow larger.
insecticidal soap
Per Cornell Cooperative Extension, insecticidal soap (2%) kills young larvae on contact. Adults are more resistant. Apply to leaf undersides with thorough coverage.
Pyrethrin and permethrin
Per Penn State Extension, pyrethrin provides fast contact kill of larvae and adults. Permethrin has longer residual activity. Apply when beetles and larvae are present and active (warm, sunny days). Observe pre-harvest intervals per the label.
Parasitic wasp — Pediobius foveolatus
Per Cornell Cooperative Extension, the parasitic wasp Pediobius foveolatus is commercially available and provides significant biological control of Mexican bean beetle when released. The wasp parasitizes larvae; parasitized larvae turn dark and fail to pupate. Per Penn State Extension, timely releases when first-instar larvae are present (approximately 100 wasps per 100 square feet) can substantially reduce larval populations.
Common problems table
| Symptom | Likely cause | Action |
|---|---|---|
| Skeletonized bean leaves, papery upper surface | Mexican bean beetle larval feeding | Check undersides for larvae; apply spinosad |
| Yellow oval egg clusters on leaf underside | Mexican bean beetle eggs | Remove and crush; prevents next generation |
| Yellow spiny larvae in groups on leaf underside | Young larvae, most susceptible stage | Apply insecticidal soap or spinosad immediately |
| Copper-yellow oval beetles with 16 spots | Adult Mexican bean beetle | Do not confuse with beneficial ladybeetles |
| Damage peaks in August | Second generation buildup | Anticipated pattern; early planting avoids peak |
Frequently Asked Questions
How do I tell Mexican bean beetle from a beneficial ladybeetle?
Per Penn State Extension, beneficial ladybeetles are typically bright red or orange with 7 spots (or sometimes 2 or 9) and have a distinctly different body color. Mexican bean beetles are copper-yellow to tan with 16 spots and have that warm brownish coloration. The host plant context is also helpful — a spotted beetle on beans in July is more likely to be Mexican bean beetle than a chance-visiting beneficial species.
Will Mexican bean beetle damage kill my bean plants?
Per Clemson HGIC, severe infestations can defoliate and kill plants, particularly in August when second-generation larvae are at peak populations. Moderate damage reduces yield but does not kill established plants. Early detection and control before populations build is more effective than trying to control a large established population.
Do Mexican bean beetles affect other plants?
Per Penn State Extension, E. varivestis primarily infests legumes: snap beans, Lima beans, soybeans, and cowpeas. It occasionally infests other plants minimally but is not a significant pest outside the bean family.
Can I attract enough natural enemies to control Mexican bean beetle without insecticide?
Per Cornell Cooperative Extension, natural enemies including Pediobius wasps and some predators can reduce populations in some situations, but natural enemy populations rarely build fast enough to prevent damage in the peak second generation. The most reliable natural enemy approach is purchasing and releasing Pediobius at the right timing.
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Recommended gear: Best Floating Row Covers for Pest Exclusion (2026) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.
Sources
- Penn State Extension — Mexican Bean Beetle
- Cornell Cooperative Extension — Vegetable Pest Management
- Clemson HGIC — Mexican Bean Beetle