Larvae have three pairs of legs (six total) and begin- feeding on prey immediately after hatching. After feed- ing on one or two prey for one or two days they molt to the protonymph stage.
Protonymphs and deutonymphs are first and sec- ond stage nymphs, respectively, that increase in size and have four pairs of legs (eight total). Each stage consumes prey over one or two days, getting slightly larger and eventually molting to adulthood.
Fig. 2. Female western predatory mite and eggs (white).2
Adult females consume about two prey per day for about five to six weeks. They deposit an average of 33 eggs during that time. Males consume about one prey per day for about four to five weeks.
Predatory mites have multiple generations per year and develop from egg to adult in 6 – 12 days. Western preda- tory mites go into diapause (dormancy) when there
are less than 11 hours of daylight. There are, however, non-diapausing strains that can be used effectively in greenhouses during short winter days. Adults overwinter in protected places, such as bark, leaves or soil debris.
Foraging:
Western predatory mites are quite versatile in that they can be used in low-growing crops such as strawberries, mid-height crops such as grapes and cane fruit, and tree fruit crops. They will attack adult, juvenile, and egg stages of many pests, such as two-spotted spider mites, Mc- Daniel spider mites, yellow spider mites, apple and pear rust mites, Prunus rust mites, blister mites, and sometimes European red mites, making them a fairly versatile gener- alist predator. They will also feed on other predatory mites and small insects. They consume their prey by piercing and sucking them dry. Amblyseius spp. also tend to be generalist while Neoseiulus cucumeris target thrips, and P. persimilis targets spider mites more specifically.
Many predatory mites supplement their diet with plant pollen, which helps limit their dispersal in the general area where they are resident or released as a biological
control agent. The additional food resource and limited mobility allows predatory mites to act as “body guards” and protect plants from pest mite outbreaks even when pest populations are low.
PROMOTING BENEFICIAL MITES
Augmentation and Inoculation:
Predatory mites can be purchased through commercial suppliers and they also occur naturally. Augmentation is the practice of timing the introduction of a fresh popula- tion of predators to help the current native population keep up with an observed or anticipated flare-up of a pest population. Inoculation is the practice of introduc- ing predators into an area where the population is low or non-existent.
When pest spider mite populations are high it is better
to apply a “soft” pesticide, such as insecticidal soap or horticultural oil, before introducing predators. This should knock the pest mite population down so the predator introduction can be more effective. If a miticide is to be used in a “hot spot” it should be applied before the intro- duction of the predators—preferably several days before the release. This strategy will improve the effectiveness of the predatory mites. Read the pesticide label to select the product that will best fit the pest management plan. It is important to note that some pesticide-tolerant strains of predatory mites are available as biological control agents.
Release process:
Several species of predatory mites can be purchased through commercial suppliers (Table 1, pg. 3). Select the predatory mite that best fits the pest management plan (e.g., target pest, greenhouse, etc.). Mites are usu- ally shipped overnight in an insulated container with an ice pack to improve survivability. When the shipment is received it should be opened and inspected as soon as possible to determine whether the mites are still alive.
The mites are typically combined with a carrier mate- rial, such as vermiculite, corncob dust, or sawdust. A light spray of water on the application area will help the mites and carrier material stay in place when they are applied to the infested area. It is best to apply them to the field, garden, or greenhouse as soon as possible to ensure their survival. To avoid extreme heat
or cold that can decrease pred-
ator success, apply them in the
early morning or late evening.
Be sure to follow the supplier’s
instructions.
Fig. 3. Predatory mites are ap- plied from a shaker container provided by the commercial
supplier.