Mexican Bean Beetle

Mexican Bean Beetle: (Size=1/4 inch)
Given their size and spots you'd be right to think "ladybug". They look a lot like their ladybug cousins, but don't be fooled. The distinctive bronze instead of red background color gives away their identity. Mexican bean beetles are fairly common in the U.S., but more prominent in the southeast and most rare in the northwest. Gardeners east of the Rockies are most familiar with them. They seek out most any variety of bean.

The adult beetle features sixteen black spots on its back. Larvae are fat, hump-backed, spiny, yellow grubs about 1/3 inch long. Both adults and larvae feed on foliage, leaving a skeleton of veins.

Adults overwinter on plant debris, emerging in late spring or early summer to lay clusters of yellow eggs on leaf undersides. There are one to four generations per year.

Controls:
Use garden fabric (row covers) over seedlings to prevent egg laying.

Check leaf undersides for masses of yellowish eggs, and squish any you spot.

Hand-pick adult beetles and larvae.

Neem oil will deter feeding adults.

Canola Spray Oil is useful against the larvae.

Pedio wasps (Pediobius faveolatus) parasitize bean beetle adults.

Toads, birds, and spined soldier bugs are general predators that attack them.

Clean up plant debris in the garden at the end of the season to reduce the number of overwintering adults. Where these beetles are a severe problem, look for varieties of beans that are naturally resistant.

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