Combat spider mites without using synthetic pesticides. Predatory mites work just as well, but without the chemical residues and toxic fumes.
Popular with greenhouse growers, predatory mites are an important beneficial “insect” for spider mite control. The body of the predator is orange-red colored, pear shaped and the front legs are longer than those of its prey. Once the predators are released, they begin feeding on pest mites, which are often most abundant on the underside of plant leaves. The predaceous females will begin laying eggs, that are about twice as large as pest eggs, which will hatch after a few days. The young predators soon join the adults to feed upon the pest eggs. Control of a light infestation should occur in two to three weeks. On heavier infestations a second release may be required.
On heavier infestations, it is important that you first reduce the pest infestation before releasing beneficial insects. Consider spraying with an insecticidal soap or other natural insect control. If only a few plants are heavily infested, consider removing them.
Listed below is a short description of four commercially available species.
Phytoseiulus persimilis – The most popular of all predaceous mites, P. persimilis does best in a humid environment of 60% to 90% and temperatures between 70 to 100˚F. It is recommended for use in most applications.
Mesoseiulus longipes – Similar to P. persimilis but is more tolerant to lower humidity (40% at 70˚F). It is a good predator for up to 100˚F, although it requires more humidity as the temperature increases.
Neoseiulus californicus – Consumes pest mites at a slower rate than either of the above species, but will survive longer under starvation conditions when pests are reduced. Will usually be present if pests re-infest plants. Needs a minimum of 60% humidity and temperatures up to 90˚F.
Galendromus occdientalis – More versatile in habitat and feeding capabilities than other species listed. It is tolerant to some pesticides including Guthion, closely related organophosphates, and Carbaryl (Sevin-R). This predator is well adapted to outdoor use and can perform in hot situations where humidity remains above 50%.
The following release rates have been established:
1 – 2 per infested leaf
20 – 30 per infested medium sized plant
1 per 5 to 10 pest mites
Note: Predaceous mites do not attack insects such as aphids, whiteflies, mealybugs, or scale. They are strictly predators of most plant feeding mites and do not injure plants or bite people. Once they run out of food, they simply starve to death.
• Learn more about spider mites here. (PDF format)
• Midwest Biological Control News – University of Wisconsin, Madison
• Phytoseiulus persimilis – Cornell University
• Natural Enemies Gallery – University of California IPM Program
• A Killer of Spider Mites – Biobest Biological Systems, Belgium