Brian Spencer discusses the amazing predatory mite Amblyseius (Neoseiulus) fallacis.

Predatory Mite (Amblyseius fallacis)

A native predatory mite that feeds on two-spotted spider mites and eriophyid mites(broad,rust, cyclamen).  Optimal environment is in a dense canopy and relative humidity of 50% or above.  Extremely effective and adaptable to a wide range of temperatures and humidities and very resistant to commonly used pesticides.

Fallacis is most effective when applied at the first sign of a mite infestation. They will usually become established in the crop after one introduction, where they remain if mites or pollen are available for food. When prey become scarce, fallacis moves to the top of the plant and usually disperses throughout the crop on air currents or the wind. When predators are found on each infested leaf, it usually means that the biological control program will be successful. It may take another 2-6 weeks for new plant growth to show improvement, depending on growth rates.

Target Pest:
 Broad Mites, Rust Mites, Cyclamen Mites, Spider Mites

Optimal Environment:

Optimum performance will be between 70-100°F with a relative humidity of between 40-90% These mites will feed at temperatures as low as 35°F and as high as 100°F. However, at the low-end of the scale (less than 50°F), they won’t reproduce, and at the high-end they need very humid conditions to work with any efficiency

Release Rates:

General release:

Apply 2-3 each per 10 square feet.


Development from egg to adult takes from 7-9 days at 70°F, to 3 days at 85°F. At 78°F, a fourfold increase in numbers can occur within 4 days. In the field, under optimum conditions, populations can increase from 10 predators per 100 leaves, to 200-500 predators per 100 leaves in just 2 weeks.

Adult females lay 1-5 eggs per day, for a total of 26-60 eggs over their lifetime (which could be between 14-62 days). The eggs hatch in 2-3 days, which are oval in shape and twice the size of the two-spotted mite eggs. Newly hatched predators do not eat, but later stages and adults feed on all stages of prey. Female Fallacis can eat 2-16 spider mites per day.

Adult females enter diapause in response to the short days in the fall (less than 14 hours of daylight). They stop reproducing and move into sheltered areas, such as under bark or ground cover. They do not enter diapause in greenhouses or interior plantscapes if the temperature is 64°F or above.

Strategic Considerations:

Neoseiulus is a food generalist, with a strong preference for other spider mites. When their favorite meal is not available, fallacis will prey on other mites and small invertebrates. Furthermore, Neoseiulus can perfectly survive on pollen. This allows growers to introduce the biocontrol agent even at low spider mite populations. In certain crops, it is even possible to maintain a year-round presence of fallacis. Neoseiulus has shown to have a relatively low susceptibility to a number of chemical crop protection products.