Neoseiulus (Amblyseius) fallacis

Target Pests: Two-Spotted Spider Mites and “friends such as spruce spider mite, southern red mite, and bamboo mite; Cyclamen Mite, Broad Mite, and Hemp Russet Mite last three mites may require additional control measures

Description: Fallacis is a native predatory mite that feeds on several different mites, including spider mites and rust mites, as well as other small insects. Fallacis may also feed on pollen, and can survive for periods on pollen alone, which makes them an excellent preventative insect. It is one of the most important biological control agents in North American berry and orchard crops. Adults are bout 0.5mm long, with pear-shaped bodies. They are tan to light orange in color, shiny, with long legs. Immature Fallacis are cream colored and semi-transparent. Eggs are oval and about 0.3mm long.

Use as Biological Control: Fallacis is used to control two-spotted spider mites (and other mites) on greenhouse peppers, field strawberries, raspberries, currants, mint, ornamentals from poinsettias to zinnias, cannabis, hemp, and hops. Fallacis can remain in areas with low levels of spider mites by feeding on other small arthropods and pollen. Fallacis feeds and reproduces over a wide range of temperatures (48-85°F). They do best where there is a dense plant canopy and when relative humidity is over 50%. Fallacis can reproduce at lower temperatures than other predatory mites and displaces them in cooler growing areas in the Northern United States. It may overwinter in minimally disturbed crops.

For Best Results: In field crops, placing higher numbers of predators on the prevailing upwind side of the crop will increase their dispersal throughout the crop via wind. In greenhouses and indoor settings, Persimilis should always be applied along with Fallacis if spider mites are already present. If spider mite numbers are high, using a pesticide with minimal residual activity such as Suffoil-X (when permitted by label, state law, and crop tolerance) to reduce pest numbers before releasing predators will help control cost. Fallacis needs a relative humidity of over 50% to survive, particularly in the egg stage. In hot, dry conditions, raise the humidity by watering or misting plants and maintaining areas of higher plant canopy density. For two-spotted spider mites in greenhouses where temperature and humidity are consistently high (over 72°F and 70% respectively), release persimilis as well as fallacis. Persimilis works better in high density spider mite populations under these conditions, but does not do well when spider mite density is low – so use persimilis and fallacis together. The mite eating lady beetle Stethorus punctillum is less affected by low humidity, and may be used along with fallacis in most crops. Stethorus is able to fly and can detect and control small colonies of mites before they become well established.

Introduction Rates: Right before you expect to see spider mites, release at 2-3 per 10 sq ft. If spider mites are present at low density, release at about 1 per sq ft. In cannabis in the vegetative stage, up to 3 per sq ft may be appropriate. Keep good scouting records though – you want the mites to get enough to eat and reproduce for optimal results - so releasing too many fallacis can mean there aren’t enough spider mites to go around. If most to all of the infested leaves also have a predator and/or spider mite egg numbers are decreasing from week to week, the outlook for the crop is good. But don’t get complacent – keep scouting weekly. As the crop environment changes over time, so can pest and predator numbers. In outdoor crops, about 10K per acre, in the spring when low and high temperatures are above the mid 40s F. Release in about 60-80 places per acre, putting more fallacis where there are more spider mites. For perennial crops, inoculate the first year only at the 10K/acre rate. Take care to avoid harming fallacis populations via insecticides used for aphid management in crops such as strawberries, mint, raspberries, and hops. Consider adding Stratiolaelaps in crops where herbicides and tillage aren’t used, as it can assist in controlling overwintering spider mite populations as well.

Neoseiulus fallacis photo rights: Applied Bio-Nomics Ltd. Photo by Dr. David Gillespie.