Know Your Friends

Hypoaspsis miles, A Predatory Mite

Hypoaspis miles is a soil-dwelling, predatory mite that is native to the United States. Hypoaspis feeds on fungus gnats, springtails, thrips pupae, and other small insects in the soil. The mite is 0.5 mm (1/50 inch) long and light-brown in color. It inhabits the top 1/2 inch layer of soil. Females lay eggs in the soil which hatch into nymphs in 1 to 2 days. Nymphs develop into adults in 5 to 6 days. The lifecycle takes approximately 7 to 11 days.

Both nymphs and adults feed on soil-inhabiting arthropods, consuming up to 5 prey per day. They survive by feeding on algae and/or plant debris when insects aren't available. Both males and females are present, but males are smaller and rarely seen.

Hypoaspis is well adapted to moist conditions in greenhouses in a variety of growing media, but does not tolerate standing water. Hypoaspis is currently used in greenhouses for control of fungus gnats. It feeds on the young fungus gnat eggs and small larvae and is most effective when applied before fungus gnat populations become established or when populations are low. It has been successfully used in bedding plant production, potted plants, and poinsettia stock plants. The mite is formulated in a pasteurized peat mixture for commercial use. They are usually sold in 1 liter containers, which contain approximately 10,000 mites of all life stages. Containers include a shaker lid which allows for distribution over the soil surface, after which Hypoaspis will burrow into the soil. One application can establish a mite population for an entire growing season under optimal conditions. A recommended application rate from IPM Laboratories, Inc. is 1 liter container per 1000 ft2. In vegetable production, recommended applications rates for cucumbers are 4 to 8 liters per 50,000 ft2 and 10 to 12 liters per 50,000 ft2 for tomatoes, with applications being made when young plants are set out in the greenhouse.

Hypoaspsis will also attack thrips pupae in the soil, but cannot be relied on for thrips control alone in a commercial greenhouse. It may, however, enchance biological control when used in conjunction with predators feeding on thrips on the foliage. In small-scale experiments this mite reduced emergence of adult thrips to about 30% of that in controls.

As with all purchased natural enemies, it is important to ascertain the quality and/or presence of mites in the container. You can do this by placing a small sample on a sheet of white paper, and examining it with a 10-15X hand lens to look for the quick-moving mites. Hypoaspis moves well on soil surfaces, so it is unnecessary to apply to all surfaces. Although they will move between plants in pots, at least every second plant should be treated. Application needs to be made early enough to allow the mite to spread. They won't move throughout an entire greenhouse from a single introduction point. Hypoaspis doesn't survive below the top 1/2 inch of soil, so mixing mites into the growing media prior to potting is not recommended. In addition, Hypoaspis doesn't store very well; therefore it should be released immediately upon arrival. The mite is compatible with insect-parasitic nematodes, such as Steinernema carpocapsae and S. feltiae, and Gnatrol, the biorational insecticide containing Bacillus thuringiensis var. israelensis.

- Raymond A. Cloyd, Purdue University

Illustration courtesy of Applied Bionomics, Ltd.
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