Mexican Bean Beetle
On Crops: Beans
Most of United States except for dry, arid climates
These large ladybeetle cousins are yellowish when they first emerge, and change to yellow-orange with black dots as they mature. Mexican bean beetle larvae are yellow, spiny, soft-bodied creatures, which develop black-tipped spines as they grow. Adults, larvae and bright yellow eggs are usually found on the undersides of bean leaves.
Mexican bean beetle adults and larvae rasp away tissues on the undersides of bean leaves, causing them to have a skeletonized appearance. In severe situations, the larvae also feed on tender young bean pods.
Mexican bean beetles have many natural enemies, which are attracted by an abundance of nectar-rich flowers. Bush beans can be grown under row covers to prevent damage. Grab and smash any adults found exploring the garden in late spring. Early crops often escape serious damage, because the second generation that emerges in midsummer is the one that sabotages garden beans.
As soon as this pest is seen, begin checking plants for eggs and larvae. Scrape them off with a dull knife. Pyrethrum-based organic insecticides can be used to bring serious infestations under control, but may also kill beneficial insects.
In some areas this pest has been eliminated through large-scale releases of Pedio wasps, a natural predator.