Predatory Mites

Mites are not insects; they are more closely related to spiders. Adults have four pairs of legs and two, rather than three, body parts. The species best known to growers are the plant-feeding spider mites. There are, however, many species of beneficial predatory mites, several of which are mass reared commercially for the management of spider mites, thrips, and other pests in greenhouses and some field-grown crops.They are predatory in both the nymph and adult stages. Predatory mites are one of the most successful commercially available biological control agents.

Appearance

Predatory mites are about the same size as spider mites, usually teardrop-shaped, long legged when compared to spider mites, and often orange-red, tan, or brown. They move quickly through and around spider mite colonies in search of prey and, unlike spider mites, can move backwards as well as forwards. Eggs are usually oval-shaped and a little larger than the spherical eggs of spider mites. Predatory mite nymphs resemble small adults.

Habitat (Crops)

Crops attacked by spider mites, thrips and fungus gnats; greenhouse crops, orchards, small fruit plantings.

Pests Attacked

Different species of predatory mites attack spider mite adults, nymphs, larvae, and eggs; thrips, mainly immatures; and fungus gnat eggs and larvae. Many species may also prey on other small insects and insect eggs.

Life Cycle

The time from egg to adult can range from a few days to weeks, depending on the temperature, humidity, and species. The commercially available species often have high rates of reproduction and short generation times, and are able to match the life cycle of their prey reasonably well. Most commercially available species do not overwinter in cold climates.

Relative Effectiveness

Predatory mites can seek out prey in places that may be inaccessible to chemical sprays. These beneficial mites are used against spider mites and several species of thrips by greenhouse flower, ornamental, and vegetable producers in Canada and Europe, and by some United States growers. Predatory mites are particularly successful in greenhouses partly because of the high degree of control that the grower has over the environment. However, several predatory species also have been used successfully to suppress spider mites in United States apple, citrus, and avocado orchards and also in field-grown strawberries and raspberries in California.

Some species of predatory mites, particularly Phytoseiulus, are among the few biological control agents that will eat all their prey and starve if they cannot locate new colonies of spider mites. Scouting is therefore important to ensure proper timing and placement when releasing the predators. It may be necessary to reintroduce the predatory mites if the pest population reoccurs. The ability of predatory mites to seek out prey can be hindered on plants with hairy stems or leaves.

Pesticide Susceptibility

Strains of some beneficial mites that are tolerant of organophosphorous and carbamate insecticides, sulfur, and pyrethroids have been selected. Some of these strains are commercially available.

Conservation

Spider mite and thrips populations are resistant to many of the chemicals used against them. Predatory mites are often very susceptible to these same chemicals. In fact, spider mites only became important agricultural pests after the widespread use of broad-spectrum insecticides in the 1950s and 1960s. Pyrethroid sprays, in particular, are known to cause spider mite flare-ups due to the elimination of natural enemies and physiological effects on the mites.

Spot spraying of localized outbreaks of thrips and spider mites with short-residual chemicals that are compatible with the predatory mites or, on a small scale, with insecticidal soap or horticultural oil may help to keep infestations under control while the predatory mite population establishes.

Commercial Availability

Predatory mites are commercially available. They are shipped as nymphs and adults in a dry carrier material such as bran or vermiculite, often with spider mite eggs as prey to prevent cannibalism. Misting the plants with water before application of the predators may help the carrier material (and predatory mites) adhere to the foliage. However, avoid watering plants immediately after application of the predators to allow them time to find appropriate niches in the foliage.

Taken from:

Hoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect Pests. Cooperative Extension, Cornell University, Ithaca, NY. 63 pp.

• Predatory Mites
  • Euseius tularensis
  • Galendromus (=Typhlodromus, =Metaseiulus) occidentalis
  • Galendromus (=Typhlodromus) pyri
  • Neoseiulus (=Amblysieus) fallacis
  • Phytoseiulus persimilis
  • Zetzellia mali
• Apple Orchard Predatory Mites
  • Galendromus (=Typhlodromus, =Metaseiulus) occidentalis
  • Galendromus (=Typhlodromus) pyri
  • Neoseiulus (=Amblyseius) fallacis
  • Zetzellia mali
• Predators Table of Contents
• Table of Contents
• Glossary
• Index
• E-mail to Editors

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