Vegetable Crop News

Biological Control of Mexican Bean Beetle in Gardens With a Parasitic Wasp

Mexican bean beetle can be a devastating pest of beans in some areas of the Midwest. The larvae skeletonize the foliage, and can completely defoliate the plants if left untreated. However, a small eulophid wasp has great potential for controlling Mexican bean beetle in small gardens, even in urban settings. The wasp, Pediobius foveolatus introduced from India, is a gregarious larval parasite that can completely eliminate the beetle in small gardens. This wasp also parasitizes another minor pest in urban gardens, the squash beetle.

In a study done in urban gardens in Washington, D.C., this wasp parasitized 97 to 100% of the Mexican bean beetle larvae in each garden by late summer. In one year no living Mexican bean beetle larvae could be found 14 weeks after parasite releases were made, and the bean plants were thriving. If inoculative releases of the wasps are made at the right time they can eliminate most Mexican bean beetle damage. In Washington, D.C. this is late June, but in some parts of the Midwest it may be later. The wasps should be released when the first generation Mexican bean beetle larvae are about half grown.

This summer Pediobius wasps were released in the students' community gardens at the University of Wisconsin-Madison. The extent of parasitism throughout this growing season is being studied, and the impact of this release on beetle populations and bean damage will be assessed next year. Unfortunately, this wasp does not overwinter in the Midwest, so it must be released each year for biological control. Pediobius is available commercially.

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