Mexican Bean Beetle

©Bob Lollo
Mexican Bean Beetle

Adult Mexican bean beetles are round little bugs that have backs that are yellow to gold to copper colored with 16 black dots in three rows down back (looks something like a ladybug with a different color). About the same size as a ladybug, they are about 1/4 inch long. Their eggs are quite distinctive and if you look under the leaves they are very yellow. The larvae, also hanging out on the undersides of leaves are orange or yellow hump-backed fuzzy critters about 1/3 inch long. Both adults and larvae chew holes in leaves. Found throughout the U.S., especially in the East and portions of the Southwest. In the North there are only one generation but as you move south there are more, with as many as four generations in the deep South. Hot, dry summers as well as extremely cold winters tend to reduce populations.

Their Growth Stages

Adults overwinter on plant debris in your yard, or in nearby woods or fields. They emerge in mid-spring to early summer to lay clusters of 40 to 60 yellow eggs on leaf undersides of the target plants; usually beans. These adults will munch on the new bean seedlings in the meantime. Beetle larvae begin to emerge when temperatures settle between 58°F and 69°F. They munch away until they become beetles and continue to feast on your beans if there are any left.

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