Mexican Bean Beetles

Mexican Bean Beetle

If you are growing beans, you have most likely already spotted these 1/4" long, yellowish brown beetles.

Not sure if you have them, but you've noticed that the leaves of your beans look skeletonized and lacy. You may not have noticed these beetles because they prefer to feed from the underside of leaves.

Flip over the leaves and you will most likely find any of the following:

The above photo shows the many stages in the lifespan of a Mexican Bean Beetle, from eggs to larvae to adult beetle.

These beetles overwinter and females begin laying eggs in the spring. Eggs will hatch in about 5-14 days and the larvae feed, grow and pupate for about 2-4 weeks.  They can produce 1-3 generations per year.

Last year I experienced both a a strong early summer and late summer generation on my green beans.

Inspect your beans daily, beetles easily pick off or will drop to the ground if disturbed. Reducing populations by smashing all stages from eggs to beetles are your best defense.

A few minutes each day inspecting your plants are all it takes to manage these beetles.

Currently, I have found many, many clutches of eggs on the undersides of my bean leaves and several larvae.   I was happy to find a few Spined Soldier Beetles also on my beans which are natural predators of the the Mexican Bean Beetle.

Spined Soldier Bug

Spined Soldier Bugs also prey on caterpillars, grubs, tent caterpillars, fall armyworms, and sawfly larvae. So don't be scared of this little guy, he is a welcome addition to the garden.

Since these beetles overwinter, our best line of defense as a community garden is to reduce their numbers by destroying them in their early stages as eggs and larvae and also destroying any adult beetles as they come along.