Biocontrol of Purple Loosestrife: Rearing Galerucella Beetles

Galerucella beetles can easily be reared for release into purple loosestrife infested wetlands in your area. (If purple loosestrife is classified as a noxious weed in your state you must obtain permission from the state Department of Agriculture or Department of Natural Resources to grow these plants.)

Root crowns of purple loosestrife are collected from wetlands and grown in pots to provide a food source for the beetles. Purple loosestrife root crowns need to be harvested in early spring-as soon as wetlands have thawed, before the buds begin to appear. It takes 3-5 weeks before plants are large enough to begin rearing beetles. Crowns can also be collected in the fall and stored in a cold room facility (approximately 40F) over the winter. To produce plants that are of sufficient size for beetle rearing, root crowns should be bigger than the size of a softball, and can be trimmed to fit into a 3-gallon pot.

For large scale projects (using 22 3-gallon pots), potted plants are grown in two 5-6 ft diameter plastic wading pools in full sunlight. Once plants begin to grow, just keep water in the pool.

For small scale projects, a similar process is followed, using 3-gallon pots with each set in its own dishpan.

Plants will need approximately 3-5 weeks to grow to the desired height before beetles can be introduced. Crowns sprout 2-3 weeks after they have been potted in early spring and then grow rather fast. When stems are at least 18 inches tall, beetles can be introduced.

Rearing structures need to be assembled before you obtain the beetles for rearing. Two "clothes-lines" are used to support screen cages for beetle rearing in the pools. Tomato cages inserted into each pot support the cages for small scale projects. No-see-um cloth or bridal veil material is used for the screen cages.

Contact your Department of Agriculture or DNR for a site where you can hand collect the beetles to begin your rearing project. The beetles are easiest to collect when they have just emerged and loosestrife is about 12-18" tall in the wetland. Beetles begin to emerge about the same time crab apple trees and lilacs begin to bloom.

The potted loosestrife plants are enclosed in the screen cages, and 10 beetles are added to each cage. Larvae complete development after 2-3 weeks of feeding. Adults emerge 2-3 weeks after larvae have entered the soil to pupate. Each pot that began initially with 10 adults will produce between 1000 and 2000 beetles. As soon as the first new adults start emerging, they should promptly be released in the field.

An ideal location for releasing beetles is on a site that is moderately to heavily infested with purple loosestrife, easily accessed, not prone to spring flooding, and preferably does not have standing water throughout the summer.

Releasing the beetles is very simple-take the entire pot with the screen cage into the field, place pots adjacent to purple loosestrife plants, remove the screen cages and shake out any adults onto nearby foliage. The pots should be left at the site for the remaining beetles to emerge on their own.

Check List for Beetle Rearing
Month Step
January-March Contact county agriculture inspector for permission to collect root crowns
April Field collection of root crowns
Culturing and maintaining host plants
Beetle rearing preparation
Contact DNR for site to collect beetles
May Collect beetles from wetland site
June-July Beetle rearing
July-August Releasing beetles into the wetland
Reporting
September Monitoring in the field and photograph sites

In many states a report must be filled out for each site where beetles are released-contact your DNR for local regulations. The site should also be monitored for beetle establishment and loosestrife decline over the years.

For more detailed instructions, request the bulletin FO-7080, "Biological Control of Purple Loosestrife," which should be printed by spring 1998. For availability and price, contact:

Minnesota Ext. Service Distr.Office
20 Coffey Hall
1420 Eckles Ave.
University of Minnesota
St. Paul, MN 55108-6069
phone: (612)-625-8173
outside Minnesota 1-800-876-8636

This publication can also be ordered from U of MN Extension's Product Catalog on the Internet.


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