Mexican Bean Beetle, Biological Control
If Mexican bean beetles have historically been a problem on your farm, you will very likely see them again this year. They may be pests on snap beans, lima beans, and, more recently, soybeans. While they are not a pest on every farm, some farms report significant damage from these pests and have to take action to prevent crop loss. Using biological control can reduce the need for insecticides.
To effectively manage any pest, it is important to understand pest identification, life cycle, and potential crop injury. For this information on Mexican Bean Beetle, please see our main Mexican Bean Beetle article.
Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England 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 (1-3 mm), 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. Adult wasps will emerge from mummies within 2-3 days of receipt. The parasitoids are shipped to farms as mummies or as adults.
Pediobius is well suited to our succession-planted snap bean crops. The first bean planting serves as a ‘nurse crop’ to establish the population of Pediobius that will be hard at work in successive plantings all summer. 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. Planning 2-3 releases at 7-10 day intervals will help ensure good timing and coverage on several plantings. After a release in the first planting, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies.
As with any biological control, make releases as soon as the pest is present, not after it has built up to damaging numbers. The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch. Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. If in doubt about the timing of the hatch, release as soon as you see the eggs – if you wait for the larvae you may be playing catch-up. 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. Mummies are frequently shipped in screen bags. Simply secure to the underside of a bean plant. IPM Laboratories recommends 160 mummies/A, split between 2 releases for light infestations, 640 mummies/A, split between 2 releases for heavy infestations and for the home garden, a minimum of 10 - 15 mummies.
Like beans, Pediobius wasps are killed by frost so annual releases are necessary. Most fungicides will not be harmful. Many insecticides will be harmful.
Plan ahead by contacting a supplier to inform them of your expected release dates and acreage.
Contact information for New Jersey source: Philip Alampi Insect Lab, Alexandra Villiard, 609-530-0309. You’ll also get advice on how to use the wasps from this office.
Green Spot Ltd., NH., www.greenmethods.com, 603-942-8925
IPM Laboratories, NY, www.ipmlabs.com, 315-497-2063
ARBICO Organics, AZ, www.arbico-organics.com, 800-827-2847
Biocontrol Network, TN, www.biconet.com, 615-370-4301
-- A.Brown, R. Hazzard