Natural Enemies Gallery

Western Predatory Mite

Hosts or Prey

Plant-feeding eriophyid (family Eriophyidae) and spider mites (Tetranychidae)

Identification

Adults are pear shaped and about 1/70 inch (0.36 mm) long. Nymphs resemble small adults, but are more oval shaped. Adults and nymphs are translucent to white or the color of their prey, commonly pale brownish or reddish.

The egg is transparent to translucent white, oval to pear shaped, and about the same length as the larva. The larva is about 1/100 inch (0.3 mm) long, wedge shaped, and transparent.

Lookalikes

Western predatory mite can generally be distinguished from plant-feeding mites by the color difference and its lack of the dark blotches found on McDaniel spider mite, twospotted spider mite, and certain other Tetranychidae. Spider mites are broader at the front, while predatory mites are broader at the rear and more active than spider mites.

Because it takes on the color of its prey, after feeding on reddish spider mites, G. occidentalis can resemble Euseius species that fed on reddish prey. Galendromus species can also resemble the generally reddish Phytoseiulus persimilis. However, mature western predatory mites are somewhat smaller than other predatory mites. Western predatory mite also closely resembles certain other Galendromus species and Neoseiulus fallacis. These predatory mites can be reliably distinguished only by an expert examination of microscopic characters.

Life Cycle

Galendromus species mites hatch from an egg and develop through a 6-legged larval stage and two 8-legged nymphal stages before maturing into adults. Adult females survive about 30 days and lay about 21 eggs. Eggs are laid on the underside of leaves, in crevices of buds, and on flowers and hatch in about 1 to 4 days.

Development time from egg to adult is 6 to 12 days, the quicker at warmer temperatures. Western predatory mite can have 8 to 10 generations per year.

Habitat

Western predatory mite occurs in field crops, fruit and nut trees, gardens, landscapes, and wildlands. It tolerates hot temperatures and low relative humidity, but survives best at cooler temperatures and humidity levels of 50% or greater. Western predatory mite can be active throughout the year in locations with mild winters. Where winters become cold, it overwinters as mated females in bark crevices and organic litter on the ground.

In comparison with Phytoseiulus persimilis, western predatory mite develops better at cooler temperatures and it tolerates a wider range of relative humidities (40 to 80%). Western predatory mite will not reduce spider mite abundance as quickly as P. persimilis can, but it can survive longer periods without prey.

Commercial Availability

Galendromus helveolus, G. occidentalis, and other Galendromus species can be purchased for release in crops such as avocado, grape, plum and strawberry. Several strains are commercially available, including a non-diapausing strain that allows control of spider mites when day length is short. Certain strains are resistant to certain organophosphate insecticides.

If purchase and release of a Galendromus species is being considered, to make this more effective control ants, reduce dustiness (e.g., periodically hose off shrubs), and avoid the application of broad-spectrum, persistent insecticides and miticides for all pests. See Natural Enemy Releases for Biological Control of Crop Pests, Protecting Natural Enemies and Pollinators, and Vendors of Beneficial Organisms in North America for more information.

Species

Over 100 species of Phytoseiidae predatory mites occur in California. These include at least 6 Galendromus species.

More Information

Scientific classification:

  • Phylum: Arthropoda
  • Class: Arachnida
  • Order: Acari
  • Family: Phytoseiidae
Western predatory mites, Galendromus (=Metaseiulus) occidentalis (top and bottom), and a twospotted spider mite, Tetranychus urticae (center), and its eggs.
Western predatory mites, Galendromus (=Metaseiulus) occidentalis (top and bottom), and a twospotted spider mite, Tetranychus urticae (center), and its eggs. Credit: Jack Kelly Clark, UC IPM Program
Western predatory mite, Galendromus (=Metaseiulus) occidentalis, feeding on a spider mite egg.
Western predatory mite, Galendromus (=Metaseiulus) occidentalis, feeding on a spider mite egg. Credit: Jack Kelly Clark, UC IPM Program
Oblong egg of a predatory mite (Phytoseiidae) next to the round egg of Pacific spider mite, Tetranychus pacificus, a plant-feeding pest.
Oblong egg of a predatory mite (Phytoseiidae) next to the round egg of Pacific spider mite, Tetranychus pacificus, a plant-feeding pest. Credit: Jack Kelly Clark, UC IPM Program
Relative size of adult western predatory mite, Galendromus (=Metaseiulus) occidentalis.
Relative size of adult western predatory mite, Galendromus (=Metaseiulus) occidentalis. Credit: see large image