Predatory Mites
Phytoseiidae
predator · mite predator · both
Last updated
Predatory mites in the family Phytoseiidae are the primary biological control agents for spider mites, rust mites, and eriophyid mites in orchards and gardens. At just 0.3 to 0.5 mm long, they are nearly invisible to the naked eye but their impact is outsized: a single Phytoseiulus persimilis can consume 5 adult spider mites or 20 eggs per day.
The Pacific Northwest is home to native species including Galendromus occidentalis and Typhlodromus pyri, both well-adapted to regional conditions. Several species are also available commercially for augmentative release. Phytoseiids are exceptionally sensitive to pyrethroid residues, which can trigger spider mite outbreaks by eliminating predatory mites while leaving pest mites largely unaffected.
Target Pests (16)
Quick Reference
Identification
Adult Description
Minute mites, 0.3-0.5 mm. Pear-shaped body, translucent to pale tan or reddish depending on prey consumed. Eight legs; faster-moving than pest spider mites. Visible under 10x hand lens as active, rapidly moving mites among slower-moving spider mite colonies. No webbing produced (unlike spider mites). A typical PNW garden not treated with pesticides hosts dozens of predatory mite species (WSU HortSense; UC IPM, 2024).
Larval Description
Six-legged larvae emerge from eggs; pass through two eight-legged nymphal stages (protonymph, deutonymph) before becoming adult. All mobile stages are predatory. Development faster than prey spider mites, enabling population growth that overtakes pest populations (UC IPM, 2024).
Size Range
0.3-0.5 mm (all stages microscopic; hand lens or microscope required)
Key Features
Pear-shaped body, faster movement than pest mites, no webbing. Distinguished from plant-feeding mites by body shape (pear vs round), movement speed, and absence of silk.
Lifecycle & Phenology
Incomplete metamorphosis: egg, six-legged larva, protonymph, deutonymph, adult. Females lay 1-5 eggs per day on leaf undersides near prey. Development is rapid: 6-10 days from egg to adult under warm conditions, faster than most prey species. This differential development rate is the key to biocontrol success—predatory mite populations can increase faster than spider mite populations when conditions are favorable. All mobile stages (larvae, nymphs, adults) are predatory. PNW key species include the native Galendromus occidentalis (western predatory mite) and Typhlodromus pyri in orchards, plus the introduced Phytoseiulus persimilis in gardens and greenhouses. Overwintering varies by species: most native species overwinter as inseminated adult females in bark crevices and leaf litter; P. persimilis lacks diapause and requires continuous prey or mild conditions (UC IPM, 2024; WSU HortSense).
| Generations per Year | Up to 7 or more; continuous overlapping generations when prey is available (UC IPM, 2024) |
| Overwintering Stage | adult |
| Egg Capacity | Galendromus occidentalis: approximately 21 eggs per adult female lifetime (UC IPM, 2024) |
| Larval Duration | 6-10 days total from egg through two nymphal stages to adult (UC IPM, 2024) |
| Development Duration | 6-10 days egg to adult at warm temperatures; faster than prey spider mites under the same conditions (UC IPM, 2024) |
| Adult Lifespan | Approximately 30 days for Galendromus occidentalis females (UC IPM, 2024) |
| Active Months | March through November for native species; year-round in greenhouses for P. persimilis |
Habitat & Conservation
Predatory mites require proximity to prey colonies on leaf surfaces. Optimal activity temperature range 15-25°C; performance drops sharply above 35°C. High humidity favors predatory mites relative to spider mites (spider mites thrive in hot, dry conditions). Undisturbed orchard and garden habitats with reduced pesticide use support diverse native phytoseiid communities. A typical PNW garden not treated with pesticides hosts dozens of predatory mite species (WSU HortSense; UC IPM, 2024).
Nectar & Pollen Sources
Conservation Practices
- Elimination of broad-spectrum insecticide applications, especially pyrethroids, carbamates, and organophosphatesTiming: Year-round; especially critical during growing seasonA single broad-spectrum application can eliminate predatory mite populations established over years, triggering pest mite outbreaks worse than the original problem. Predatory mites are more sensitive than pest mites to most broad-spectrum products
- Maintenance of undisturbed refuge areas (hedgerows, unmowed orchard floors) adjacent to managed plantingsTiming: Year-roundRefugia harbor overwintering phytoseiids that recolonize managed areas in spring
Pesticide Sensitivity
| Product Class | Impact | Notes |
|---|---|---|
| Pyrethroids bifenthrin, lambda-cyhalothrin, deltamethrin | lethal | Almost all pyrethroids show higher toxicity to predatory mites than to spider mite prey, creating conditions for pest mite outbreaks ('mite flare') |
| Neonicotinoids imidacloprid, acetamiprid | moderate | Variable toxicity by specific compound; toxicity endpoints of most neonicotinoids exceed field rates but some compounds reduce predatory mite abundance. Acetamiprid more harmful than thiacloprid |
| Carbamates carbaryl | lethal | Highly toxic to all phytoseiid species; a primary driver of secondary mite outbreaks in orchards |
| Organophosphates malathion | lethal | Highly toxic; responsible for classic 'mite flare' when applied to orchards |
| Horticultural oils mineral oil | low | Contact only; low residual. Compatible with predatory mite conservation when applied at proper dilution rates |
| Insecticidal soaps potassium salts of fatty acids | low | Contact only; minimal residual after drying |
| Azadirachtin (neem) azadirachtin | low | Among the safest options for IPM compatibility with predatory mites |
Commercial Availability
Phytoseiulus persimilis: typical release rate 2-5 per plant or 50,000-100,000 per hectare for established infestations. Neoseiulus californicus: 25,000-50,000 per hectare preventive (commercial guidance; UC IPM, 2024)
Introductions most effective early in spider mite season before pest populations reach damaging levels. June releases optimal for PNW outdoor gardens (UC IPM, 2024)
Phytoseiulus persimilis is the foundation biocontrol agent for spider mites in greenhouse systems since the 1950s. In outdoor PNW gardens, June introductions can establish self-sustaining populations through the growing season if pesticide exposure is minimized. Native Galendromus occidentalis persists year-over-year in PNW orchards when broad-spectrum sprays are eliminated (UC IPM, 2024).
Live mites are perishable; immediate deployment after receipt recommended. Brief storage possible at 50-60°F for 1-2 days maximum (commercial product literature)