Biological Control : A Guide to Natural Enemies in North America Anthony Shelton, Ph.D., Professor of Entomology, Cornell University
 

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Phytoseiulus persimilis
(Acarina: Phytoseiidae)

Phytoseiulus persimilis, a predaceous mite, is one of the mainstays of greenhouse integrated pest management programs for control of spider mites on vegetables and ornamentals in Europe, North America, and elsewhere. This mite was accidentally introduced into Germany from Chili in 1958 and subsequently shipped to other parts of the world, including California and Florida, from Germany.

Appearance

Although extremely small (approximately 0.5 mm or 0.02 inches), P. persimilis can be distinguished with a hand lens. It is fast moving, orange to bright reddish orange, has a teardrop-shaped body and long legs, and is slightly larger than its prey. Immatures are a pale salmon color. Eggs are oval, approximately twice as large as the pest mite eggs.

(Note: in the winter, the twospotted spider mite also develops a reddish color, although two dark spots on its abdomen usually distinguish this pest from other mites.)

Habitat

Greenhouses, interior plantscapes, and crops where twospotted spider mites are a problem.

Pests Attacked (Host Range)

This species is a specialized predator of web-spinning spider mites such as the twospotted spider mite. In fact, P. persimilis feeds, reproduces, and completes development only on mites in the subfamily Tetranychinae, although it also feeds on young thrips and can be cannabilistic when spider mite prey is unavailable.

Life Cycle

P. persimilis eggs hatch in 2-3 days, and although the larval stage does not feed, the subsequent nymphs and adults feed on all stages of prey. Total time from egg to adult ranges from 25.2 days at 15°C (59°F) to 5.0 days at 30°C (86°F).

The adult female may lay up to 60 eggs during her 50 day-long lifetime at 17-27°C. Generation times of from seven to 17 days are possible, depending on temperature and humidity. Due to its tropical origin, P. persimilis does not have a diapause stage and is active year-round in enclosed habitats such as interior plantscapes and greenhouses.

Relative Effectiveness

Adult P. persimilis eat from 5-20 prey (eggs or mites) per day, they reproduce more quickly than the spider mites at temperatures above 28°C (82°F), and they feed on all stages of the twospotted spider mite. P. persimilis are very voracious. They have the highest consumption rate of all phytoseiids. However, they absolutely must have spider mite prey or they will disperse and/or starve.

Almost 75% of European greenhouse vegetable production relies on P. persimilis for spider mite control, and the California strawberry industry uses this mite, along with another beneficial mite, Neoseiulus (=Amblyseius) californicus, to control spider mite infestations in field-grown strawberries. It is also used in interior plantscapes and conservatories. Greenhouse ornamentals growers have long relied on its ability to control spider mites.

Humidity strongly impacts P. persimilis' efficacy. Development was observed to almost stop at humidities of 25-30%, and relative humidities below 70% resulted in a reduction in the ability of immatures to molt from one stage to another. In one study, at a relative humidity of 40% (temperature 27°C), only 7.5% of eggs hatched compared to 99.7% at 80% relative humidity (same temperature). Eggs held at a relative humidity of 50% appeared to shrivel at all temperatures from 13-37°C.

Phytoseiid mites use odors (kairomones) associated with mite-infested plants to locate their prey. When P. persimilis contacts spider mite webbing, it intensifies its search for prey.

P. persimilis has high dispersal ability and its distribution is highly correlated to that of its prey. However, its ability to disperse is dependent on the environment. If infested plants' leaves touch, dispersal is possible. When the plants have little contact with each other, dispersal is reduced by about 70%. P. persimilis moves upward on the plant in search of prey and disperses when prey is scarce. Nymphs do not disperse easily, and are left behind when prey becomes scarce.

Because these mites are such efficient hunters and dispersers, they can cause extinction of their spider mite prey. This is desirable where little or no spider mite damage can be tolerated, such as in ornamental plants. However, in crops where some plant damage is acceptable (e.g., tomatoes and cucumbers), it is desirable to have a stable interaction between predator and prey over an extended period of time.

Typically, P. persimilis will eventually exhaust its food supply and starve, and so it must be reintroduced.

Conservation

Relative humidities greater than 60% are required for survival of the predator, particularly through the egg stage.

For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, Feature Article on conservation in Volume II, No. 1 of Midwest Biological Control News.

Pesticide Susceptibility

Strains that are tolerant of some insecticides have been selected.

Commercial Availability

Widely available (see the off-site publication, Suppliers of Beneficial Organisms in North America, page of the California Department of Pesticide Regulation website).

Taken from:

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

Additional Reference

Applied Bio-Nomics Ltd. (1993) Biological Technical Manual. Applied Bio-Nomics Ltd., Sydney, BC.

Central Florida Research & Education Center, Biological Control - Section 3: Phytoseiulus persimilis.

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P. persimilis adult, courtesy of  Buglogical Control Systems. PHOTO: Max Verkooy

P. persimilis adult, courtesy of
Buglogical Control Systems.
Photo: Max Verkooy

   
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