Insect Management

Mexican Bean Beetle

MEXICAN BEAN BEETLE: A CHANCE FOR BIOLOGICAL CONTROL

First plantings of snap beans are usually up and growing by early June. Mexian bean beetles will colonize beans later in June. The coppery brown, round, spotted adults, which look like large ladybeetles, lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage of adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season.

A beneficial insect, Pediobius foveolatus, is commercially available for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among Massachusetts growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. This small (1-3mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies.

The New Jersey Dept of Agriculture Insectary recommends two releases, two weeks in a row, timed for the beginning of egg hatch. Wasps will lay eggs in larvae of any size, but it is best to target the young MBB larvae, before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for first hatch. The release rate should be at least 2000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more. Cost from NJDA is $30 plus shipping for 1000 adults, or $15 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge. If you already have MBB larvae, order adults. Ship for overnight delivery. Instructions for handling and release will come with the wasps.

Wasps reproduce in the field and are still present when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost.
Contact information for New Jersey source: Tom Dorsey, 609-530-4196 or 530-4192; address NJDA Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628. You’ll also get advice on how to use the wasps from this office.

Pediobius should also be available from the following suppliers: Green Spot Ltd., NH., www.greenmethods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Biocontrol Network (TN), 615-370-4301, http://www.biconet.com/ ; Rincon Vitova (CA), 800-248-2847, http://www.rinconvitova.com/.

For more information on insecticides for Mexican bean beetle control, visit the New England Vegetable Management Guide.

--R. Hazzard, University of Massachusetts Vegetable Program

Updated June 2007