Target Pest: Two-Spotted spider mite (Tetranychus urticae)
Description: “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.
Use as Biological Control: Persimilis is very effective against two-spotted spider mites in greenhouse vegetables and ornamentals, interior plantscapes, and conservatories. It can also be used in warm climates on field crops such as strawberries. Optimum conditions are 68-81°F (20-27°C) 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.
Monitoring Tips: Persimilis is usually easy to tell from its prey. Two-spotted spider mites are pale green, with two darker spots on their sides, and move quite slow. In winter, some two-spotted mites turn a reddish color, but can still be distinguished from persimilis by their slower movements.
Life Cycle: The complete life cycle of persimilis can range depending on the temperature. At 86°F (30°C), it takes 5 days, and at 59°F (15°C), 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.
Introduction Rates: 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 (m2) or 20 persimilis per infested leaf, weekly, as needed. Apply predators to each infested plant.
For Best Results: If spider mite numbers are high (there is visible webbing and clusters of mites stringing down from leaves), use a compatible pesticide such as fenbutatin oxide or insecticidal soap before releasing predators.
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.
Note: Unlike fallacis, which can survive on pollen during times with low populations of prey, persimilis will only be sustainable on mites. If there are none to feed on, persimilis will starve to death- meaning they will not do well for preventative measures.