Mexican Bean Beetle

• Lacy skeletonized leaves with only the upper leaf surface remaining — a papery, tan skeleton
• Oval, yellowish-orange beetles with 16 black spots feeding in groups
• Yellow, spiny larvae clustered on leaf undersides
• Yellow oval egg masses on leaf undersides
• Beans may be defoliated quickly in severe infestations

Mexican bean beetle resembles a ladybug in shape but is a pest, not a beneficial insect. Adults overwinter in leaf litter and woodland edges, emerging in late spring. Eggs are laid in clusters on leaf undersides; larvae feed through four instars before pupating on the plant. Two to three generations can occur per season. Populations tend to be heaviest on bush beans in late summer.

1. 01Scout leaf undersides starting when plants emerge — yellow egg masses are easy to see and crush
2. 02Hand-pick adults and larvae; they're slow-moving and easy to collect into soapy water
3. 03Parasitic wasps (Pediobius foveolatus) are available commercially and are effective in warm climates — check with your extension office for local sources
4. 04Neem oil or insecticidal soap applied to leaf undersides reduces larval populations
5. 05Spinosad is effective against larvae
6. 06Plant early successions to avoid peak late-summer pressure; plant resistant varieties like 'Wade' or 'Logan'

If infestations are severe enough to defoliate plants before pods mature, and you're relying on beans as a significant crop, an extension advisor can advise on whether Pediobius releases are practical in your climate zone.

• Mexican Bean Beetle— Penn State Extension
• Bean Pests — Mexican Bean Beetle— University of Maryland Extension