News and Reviews

Grow Your Own Predatory Mites

Predatory mites in the family Phytoseiidae are important natural enemies of various pest mites, especially spider mites such as European red mite in orchards and twospotted (and other) spider mites in greenhouses and on landscape plants. Several species of predatory mites are available from commercial insectaries, but their cost is relatively high. The 6-page Michigan State University publication, Rearing Predator Mites for Orchards and Glasshouses, explains how to raise your own predatory mites and how to use them for biological control in orchards and greenhouse vegetable crops.

The rearing process involves growing Henderson bush lima beans in 1-gallon plastic bags. The bags, with holes poked in the bottom, are held in trays of water. The plants can be grown in a greenhouse or under fluorescent lights. Ideal conditions for fastest growth are 75-100F and 16 hours of daily light. New sets of plants are germinated weekly. When the plants are 4-6" tall, they are infested with twospotted spider mites. Two to three weeks after infesting the plants, a few heavily infested leaves are removed to infest the new batch of 6" tall bean plants. About 3-4 days after infesting a batch of plants with spider mites, these plants can be inoculated with predatory mites. The paper discusses a local species native to the upper Midwest, Amblyseius fallacis, but many phytoseiid mites can be raised using the same process. After the plants are about 15" high, they are harvested and used to inoculate younger plants that had been infested with twospotted mite. After the stock colony is established, excess plants with predators can be moved to the orchard or greenhouse for biological control.

The publication describes release methods and rates of release, as well as how to monitor to determine the effectiveness of the released predators. Also included with the publication is a pullout wall chart that summarizes the predator production and release schedule. The publication goes into great detail about the rearing methods, and discusses pitfalls to avoid. For example, the spider mites and predator mites should not be raised in close proximity because the predators can easily comtaminate the spider mite stock plants. The publication is well illustrated with drawings depicting important aspects of rearing, release and monitoring.

The publication, numbered E-1872, was written by N. Cushing and M.E. Whalon. It is available for $1.60 (postage paid) from Michigan State University Extension Service. Orders for individual copies must be prepaid. Call their Bulletin Office at 517-355-0240 for additional ordering information.

- Dan Mahr, University of Wisconsin - Madison

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