Phytoseiulus persimilis is a predatory mite used in biological pest control. It is specifically employed to manage spider mites in environments such as greenhouses and home gardens. It offers an environmentally sound method for pest management, reducing reliance on chemical treatments.
A Specialist Spider Mite Predator
Phytoseiulus persimilis is a specialized predator, primarily targeting web-spinning spider mites, most notably the two-spotted spider mite. Unlike generalist predators, P. persimilis relies almost exclusively on these specific prey for its survival and reproduction. This dietary specialization makes it an effective biological control agent.
These mites are 0.5 millimeters long, pear-shaped, and are bright reddish-orange with long legs, making them distinguishable from their smaller, paler prey. P. persimilis exhibits active hunting behavior, moving across plant surfaces in search of spider mites. Upon encountering spider mite webbing, their search intensity increases, and they navigate through the silk to access prey.
The predatory mites feed on all life stages (eggs, larvae, nymphs, and adults) of spider mites, though they show a preference for eggs. An adult female P. persimilis can consume 5 to 20 spider mite eggs or individuals per day, depending on temperature and prey availability. Their life cycle is fast, completing development from egg to adult in 4 to 7 days when temperatures are between 20 to 25 degrees Celsius (68 to 77 degrees Fahrenheit). This rapid development, twice as fast as their spider mite prey, enables P. persimilis populations to grow quickly and suppress an infestation.
Creating the Right Environment for Success
Suitable environmental conditions are important for Phytoseiulus persimilis to control spider mites. These predatory mites originate from tropical regions; they remain active year-round in controlled environments like greenhouses. Optimal temperatures for their activity and reproduction range from 20 to 27 degrees Celsius (68 to 81 degrees Fahrenheit). Though they tolerate temperatures as low as 15 degrees Celsius (59 degrees Fahrenheit), their effectiveness improves within this warmer range.
Humidity levels are also important for their survival and reproduction. A relative humidity above 60 percent is suitable; the ideal range is 60 to 90 percent. High humidity is important because it helps prevent the desiccation of their eggs, ensuring a greater hatch rate. Conversely, dry, warm conditions can impede their ability to control spider mites, and temperatures exceeding 30 degrees Celsius (86 degrees Fahrenheit) can reduce their feeding activity, with feeding ceasing above 35 degrees Celsius (95 degrees Fahrenheit).
How to Use Phytoseiulus Persimilis Effectively
For effective spider mite control, Phytoseiulus persimilis should be released at the initial signs of a spider mite infestation. Early detection is important, such as when two spider mites are observed per leaflet or when 25-35 percent of plant leaflets show signs of infestation. These predatory mites are shipped in containers.
Upon arrival, the mites should be distributed directly onto infested plants, focusing on areas with visible spider mite activity or webbing. They tend to move upwards on plants in search of prey and disperse more easily when plant leaves are touching, allowing them to spread across a crop. General release rates can vary, with recommendations ranging from five predatory mites per square foot for low to moderate infestations, to ten or more mites per square foot for high infestations where webbing is prevalent.
Most chemical pesticides can be detrimental to Phytoseiulus persimilis. Avoid pesticide applications prior to or during their release, or observe a sufficient waiting period after any spraying. Once their spider mite food source is depleted, the P. persimilis population will decline due to starvation or dispersal, as they cannot survive long without their specific prey.