Phytoseiulus persimilis.jpg

Predator Mite (Phytoseiulus persimilis)

P. persimilis is one of the oldest beneficials in use. It was originally used in the 1930’s. It is still one of the best beneficial insects, capable of complete eradication of prey. “Persimilis” is a tropical predatory mite that was one of the first greenhouse biological control agents available commercially. Adults are bright reddish-orange in color, with long legs and pear-shaped bodies (about 0.5mm long). Immature predators are a pale salmon color. Eggs are oval and about 0.3mm long, which is about twice the size of the spider mite eggs.

P. persimilis' optimum performance will be between 70-85°F with a relative humidity of between 60-90%. Optimum conditions are 68-81°F and relative humidity from 60-90%. While these are optimum conditions, they are not necessarily essential for Persimilis to be successful. Please note however, that cooler or warmer temperatures may affect reproduction and development. At optimum temperatures, the predators reproduce faster than spider mites, while at warmer and cooler temperatures, the spider mites will reproduce faster.

Target Pest:
Spider Mites, Eggs, Nymphs and Adults

Release Rates:
Release immediately for best results. It is best to release Phytoseiulus persimilis in late evening on the day you receive them. Before releasing, gently rotate the jar to distribute the mites evenly within the carrier. Next, open the jar in the crop and gently tap the contents out of the jar as evenly as possible onto the foliage of the plants you wish to treat. Concentrate the bulk of them on or near the most heavily infested plants. In trees, sprinkle them into Dixie-like cups wedged into, or distribution boxes hung from, the branches. Leave the bottle in the treatment area for 24 hours after release to ensure all Phytoseiulus persimilis have exited.

General release:

Apply 5 each per 10 square foot

Persimilis is most effective when applied at the first sign of a two-spotted mite infestation. Because of its high reproduction rate, persimilis usually exhausts its food supply and eventually dies out. Therefore, repeated introductions are recommended until all sites with spider mite infestations have persimilis present. General Introduction Rates: 5 persimilis per 10 ft2 or 20 persimilis per infested leaf, weekly, as needed. Apply predators to each infested plant.

The complete life cycle of persimilis can range depending on the temperature. At 86°F, it takes 5 days, and at 59°F, it can take 25 days. There are 4 times as many females in the population (sex ratio is 4:1 female). Females lay 2-3 eggs per day, with an average of 60 eggs over a 35 day lifetime. The eggs hatch in 2-3 days. Newly hatched predators do not eat, but later stages and adults feed on all stages of the mites. Each predator consumes between 5-30 prey per day. Persimilis do not diapause; therefore remain active all year round in greenhouses.

Strategic Considerations:
Cannabis applications vary based off of infestation level, previous chemical residue (where Persimilis is no longer recommended to use), size of plants, temperature and humidity. If there are high levels of spider mites, playing catch up becomes difficult for cannabis growers as as clean up may take at least 2 weeks to see results. For heavy infestations, remove the most affected plants and treat with GRAS or organic spray. Wait 48 hours after application of spraying to release predatory mites.

Persimilis needs relative humidity greater than 60% to survive (especially in the egg stage). If humidity is too low, raise it by lightly misting plants or wetting skywalks. Where humidity is below 60%, the predatory beetle Stethorus punctillum can be used with persimilis. Stethorus feeds on all stages of spider mite and is effective at detecting individual mite colonies. If average temperatures are often below or above the 68-81°F range for optimum use of Persimilis, introduce Amblyseius fallacis along with persimilis.

Selected References

University of California IPM