Mexican Bean Beetle

Description

Adult: Adult beetles are a bright red color (sometimes orange or brown) with a hemispherical shape and 16 black spots on their back. They are 8 mm long and 6 mm wide.  
Egg: Eggs are laid in clusters of 40-60 on the underside of host leaves. They are elliptical-shaped and yellow-orange.
Larva: Upon hatching, larva are yellow and covered with dense branched spines. They develop through four instars before pupating.
Pupa: Pupae are yellow-orange and bear brown-black lines. Pupation lasts 8-10 days.

Life History

Mexican bean beetles are related to lady beetles and have one to three generations per season in Utah. Adults overwinter in woody areas near legume production.

Damage

Both Mexican bean beetle adults and larvae cause lacy defoliation by feeding and stripping away the lower layer of leaf tissue. Eventually, this leads to skeletonization and total defoliation.

Management

Cultural

• Search for egg masses on host crops and crush them by hand. One egg mass per 1 foot is the standard insecticide threshold for fields.
• Grow early-maturing bean varieties. Avoid peak Mexican bean beetle damage in late July and August.
• Plant resistant bean varieties. Non-waxy varieties such as ‘Regal’ and ‘Idaho Refugee’ snap beans, and ‘Baby Fodhook’ and’Baby White’ lima beans are more resistant compared to waxy varieties.

Biological

The beneficial parasitoid wasp Pediobius faveolatus is a natural enemy of the Mexican bean beetle.