Guess the Pest! Week #18-19 Answer: Mexican Bean Beetle

Guess the Pest Week #18-19 Answer: Mexican Bean Beetle

Mexican bean beetle larva

Mexican bean beetle larva

Mexican bean beetle adult

Feeding injury from Mexican bean beetle

This Guess the Pest was challenging for some because we don’t typically have too many problems from Mexican bean beetles and there is a good reason for that. That reason being Biological Control.

Mexican bean beetle adults and larvae are considered a pest of beans, including soybeans, lima, and snap beans. They feed on the underside of leaves, removing the lower epidermis giving the leaves a lacy appearance. Eventually, the upper epidermis dies, and falls out to give the leaves a skeletonized appearance. Mexican bean beetles overwinter as adults in wooded areas or under plant debris. The adults emerge in the spring and lay eggs on the underside of leaves. Within two weeks, larvae hatch, and begin feeding on plant foliage.

Mexican bean beetles have been successfully controlled in our region by Pediobius foveolatus, a small parasitoid that attacks Mexican bean beetle larvae. These efforts have been led by the New Jersey Department of Agriculture since the 1980s. The parasitoids are reared at the Phillip Alampi Beneficial Insect Laboratory and released each summer because the parasitoid does not overwinter in our region. Despite the success of biological control in preventing Mexican bean beetles from requiring insecticide applications in soybeans throughout much of the region, there are a few hot spots that have occasional problems from this pest.

If you are experiencing an economic infestation of Mexican bean beetles, consider releasing the biological control agent, Pediobius foveolatus, to keep those populations in check. For more information on how, when and where to purchase Pediobius foveolatus for release, please contact Alexandra Villard at .

The threshold for Mexican bean beetles during bloom-pod fill stages in soybeans is 15% defoliation. Once the seeds are fully developed, the threshold is 35% defoliation.

Here is a link for chemical control options if your fields are at threshold for Mexican bean beetles:

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