persimilis | Bioworks

Biocontrol Organism: Phytoseiulus persimilis

The common horticultural pest in a wide range of crops; Two Spotted Mite (TSM), Tetranychus urticae or red spider mite, can be very hard to control.

A short life cycle allows it to rapidly build up resistance to insecticides. Living on the underside of leaves makes good spray coverage and early detection very difficult.

The predatory mite Phytoseiulus persimilis is used for the successful management of TSM and has been commercially produced for over 20 years in Australia.

Even though they are only slightly larger than their prey an adult persimilis (predatory mite) devours up to twenty young or seven adult TSM each day. Under optimum conditions they will multiply twice as fast as TSM.

Phytoseiulus persimilis

persimilis has been produced commercially for over 20 years in Australia. It feeds voraciously on all stages of twospotted mite, and this has led to its use in a wide range of crops.

persimilis thrives in warm, humid and semishaded conditions. The adult is orange, whereas the younger stages are clear. Both forms are pear-shaped and fast-moving. Its eggs are oval, tinged with orange, and twice the size of spider mite eggs.

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 may develop 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.

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 Californian & Australian strawberry industry uses this mite 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.

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 should Spidermite investations reoccur.