Phytoseiulus persimilis
A fast, long-legged, orange-red predatory mite about 0.5 mm long that eats nothing but spider mites, and eats them faster than any other predatory mite on sale. It is the standard curative release for two-spotted spider mite in greenhouses, on houseplants and in strawberries. It breeds about twice as fast as its prey, but it cannot live without it and it wants humid air — so it is released onto mites you have already found, not kept in reserve.
At a glance
- Mode
- Specialist predator — nymphs and adults
- Rate
- 2–50 /m² per release (Koppert); 100+ /m² on hot spots (Biobest data sheet)
- Ships as
- Adults and nymphs in wood chips, sawdust or vermiculite
- Temp
- Best 13–27 °C, poor above 30 °C (Koppert); Biobest 12–35 °C
- Humidity
- Above 70% RH (Koppert, Biobest); eggs fail below about 60%; Cornell says 50–70%
- Setting
- Greenhouse, indoor, strawberries
How it works
Nymphs and adults pierce spider mites and suck them out, and they take every stage. The newly hatched larva does not feed. Suppliers give daily intakes of up to five adult spider mites or 20 eggs and young (Koppert, at about 20 °C) and 20–25 eggs, 20–30 larvae and nymphs or 5–7 adults (Biobest). It finds colonies by the smell of mite-damaged leaves and walks through their webbing, and it spreads through a crop where leaves touch.
Its speed is the point. Egg to adult takes about 25 days at 15 °C, 9 days at 20 °C and 5 days at 30 °C — roughly twice as fast as the spider mite — and a female lays up to 60 eggs over a life of about 50 days (UC IPM, K-State; Biobest gives 50–60 eggs and a life of 30–35 days). It has no resting stage. But it is a strict specialist of Tetranychus spider mites: once the spider mites are gone it eats its own kind, disperses or starves, so it does not stay on as protection. Humidity limits it too. UC IPM reports that below 70% the young struggle to moult, and that development almost stops at 25–30%. Sources differ on the ideal: Koppert and Biobest want more than 70%, UConn more than 75%, K-State 60–90%, and Cornell 50–70%.
Is it established?
Check the hot spots you released onto, with a 10× lens on the leaf undersides. Predators are orange-red, pear-shaped and quicker than the spider mites, and have no dark side-blotches.
- DAY 1Live, fast-moving orange mites on the leaves where you shook them out
- DAYS 2–4Oval predator eggs, about twice the size of the round spider mite eggs, among the colonies
- WEEK 1All predator stages in the hot spots; shrivelled, sucked-out spider mites and eggs
- WEEKS 2–3Colonies shrinking and new growth clean; release again only if mites return
Release & handling
Mites arrive as adults and nymphs in a bottle of carrier and should go out the day they arrive: packed without food they eat each other. Koppert allows one to two days at 8–10 °C, dark, with the bottle on its side; Biobest 6–8 °C at high humidity; Arbico says to use them within 18 hours, and Sound Horticulture not to cold-store them for more than eight.
Release the same day
Tip a little carrier onto white paper and check for moving mites. If you must wait, keep the bottle cool, dark and lying flat.
Mist the leaves
A light mist stops the mites falling off (K-State), and in dry air it helps their eggs hatch (Biobest).
Onto the colonies
Turn the bottle gently to mix, then sprinkle carrier onto infested leaves and the plants around them. Leave it on the leaves for a few hours.
Repeat weekly
Release again after a week: Koppert repeats once or twice, and Biobest's data sheet gives at least two releases on hot spots; and keep the air humid.
Pesticide sensitivity
Broad-spectrum residual insecticides and some miticides kill it. Cornell lists bifenthrin, fenpyroximate and acequinocyl as ones to avoid; bifenazate, etoxazole, hexythiazox and spiromesifen as compatible miticides. Check a product →
When to choose something else
Phytoseiulus is the fastest cure for spider mites, but not the right one everywhere. Choose something else when:
- No spider mites have been found yet — it has nothing to eat and will die out; Neoseiulus californicus survives on pollen and other prey
- The air is hot and dry, above about 29–30 °C with humidity under 40% — UConn says californicus copes better with heat and humidity swings
- The crop is tomato — its glandular hairs reduce the predator's spread, survival and breeding, so expect weaker control
- The mites are broad, cyclamen or russet mites — it eats only spider mites
- Temperatures are low, around 12 °C and under — Amblyseius andersoni tolerates cooler temperatures than other predatory mites
Where to buy
Suppliers listed alphabetically, not ranked. helpfulbugs takes no commission and does not sell insects.
- Arbico Organics2,000 / 4,000 / 6,000 / 10,000US
- BioBee (BioPersimilis)2,000 / 4,000IL / EXPORT
- Biobest (Phytoseiulus-System)2,000 / 10,000 / 20,000EU / NA
- Dragonfli2,000 to 25,000UK
- Koppert (Spidex)2,000 / 10,000GLOBAL
- Sound Horticulture2,000 to 25,000US
Phytoseiulus persimilis by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.