Farm Calls: Biocontrol of Mexican Bean Beetle

This past week a grower called to ask about a recurring problem,

We’ve got a problem that hits us every year in our snap beans that we grow to sell at the local farm markets. Around June we experience heavy losses due to Mexican Bean Beetle. Somebody mentioned using parasitic wasps as a possible control agent.
What do you know about this and how do we go about getting them?

Mexican Bean Beetle: Adult and Larva

Mexican Bean Beetle:
Adult and Larva

Mexican bean beetle (MBB) has been a serious bean pest for decades in the Mid-Atlantic region, causing intolerable yield reductions. Fortunately, the Phillip Alampi Beneficial Insect Rearing Laboratory at the NJ Department of Agriculture rears small wasps (Pediobius foveolatus) that parasitize young Mexican bean beetle larvae before they can cause significant defoliation damage. The NJDA program saves about 21 tons of pesticide applications that would cost farmers about $450,000 a year. This program was so remarkable that in the 1980s and early 1990s, Ag Agents in South Jersey saw a profound decrease in grower calls regarding scouting and treatment for MBB damage across the more than 100,000 acres of soybean, snap bean and lima bean fields in the area. The Alampi Lab rearing and release IPM program was so effective that we stopped thinking about MBB as a pest that required chemical control – it just dropped off our radar screen.

NJDA staff members Mark Mayer and Wayne Hudson continue to work with Jersey soybean growers each year, refining their sampling and release programs. As noted in their 2013 Mexican Bean Beetle report, approximately 40 field release sites received about 8,000 wasp parasites per site. In fact, Mark informs me that they are already making parasite releases at an organic farm near this bean grower. It is not too difficult to add a release site, which increases area effectiveness. For optimal results, the wasps are released after Mexican bean beetle eggs hatch to larvae, but before the density of adults exceeds just 1 adult per square yard.

An excellent summary of the release program, Using Pediobius foveolatus as a Biological Control for Mexican Bean Beetle on Organic Vegetable Farms, answering questions on how, when and where to sample NJ fields as well as to make releases, was prepared years ago by Kim Stoner at the Connecticut Ag Experiment Station. For smaller market gardeners who want to purchase and release parasite, Maryland has guide on sampling and release timing.