Stratiolaelaps scimitus (formerly Hypoaspis miles) is a soil-dwelling mite capable of the prevention, control, and management of sciarid flies, shore flies and various thrips and soil pests. Not only are these mites predators of thrips’ prepupal and pupal stages, they are very effective fungus gnat predators as well. S. scimitus are shipped as adults, immatures and eggs in liter-size shaker canisters filled with a loose vermiculite carrier and a percentage of clean peat, and some bran added for good measure. In this form, S. scimitus are very easy to distribute in the crop. S. scimitus can help prevent thrips from becoming intolerable.
These robust 0.8 mm. richly-colored tan to brown mites live, eat and reproduce in the soil or soilless medium in containers and planters and, on the walkways and floors of greenhouses (or on the Shiitake logs in the mushroom scenario). The S. scimitus females’ eggs — of which there are many — hatch into super small larvae which develop into tiny dark brown, almost black, nymphal forms before reaching adulthood. These, too, are fierce predators, consuming many pests, mostly the eggs and smaller larvae (first and second instar) of fungus gnats and the pupal stages of thrips. The life-span of these predators is about 13 days from egg to adult. But they reproduce profusely in what little time they have. The conditions for optimum performance will be between 60-72°F, and we’re talking about soil temperatures, with a relative humidity equal to that found in a friable, slightly moist medium, compost or soil. But these are optimum conditions, and not necessarily a prerequisite of successful implementation. Please note, however, considerably cooler temperatures will hamper reproduction and development a certain degree.
S. scimitus are very cost-effective. A little bit goes a long way and they can last such a long time. These predators, like Amblyseius (=Neoseiulus) cucumeris, are supplied with some mold mites (Tyrophagus putrescentiae). These mold mites are merely a non-sustainable food source (but only after the contents are distributed; left in the bottle the mold mites will reproduce) for the predatory mites while they’re in transit and in storage. That’s right, storage, you can give a half-liter bottle to each interiorscape tech; the bottles store for two weeks. They just go about their business, feeding on the mold mites and their own dead and miscellaneous stuff. Fair humidity in storage is helpful, and the techs can’t leave the bottles in their cars, etc. These predators are compatible with many insecticides; a real plus in an Integrated Pest Management (IPM) program. Part of the reason for this is simple: these mites are protected in the soil during spraying. They do wander at night, though, so caution is still advisable. This wandering, however, has its advantages: the mites can usually establish themselves in the entire area.
For fungus gnat control, 6" pots and up are probably the best bet for containerized plant applications. If they’re smaller than that, we normally recommend parasitic nematodes. For thrips control, however, it is best to use the mites in nearly every application — but not alone. The thrips’ in-ground stages make up only a small percentage of their overall life-span. This is why the S. scimitus can only handle about 30% of the overall population. An above-ground predator, like Amblyseius (=Neoseiulus) cucumeris really should be used. However, let it be known that the impact of S. scimitus on this extremely pernicious pest is noticeable at worst. 30% is 30%! Do not rely entirely on the long-term establishment of S. scimitus. This happens, almost always to a certain extent, but not necessarily to such a degree that pest control can be maintained. Multiple and regular releases are, like it is for our other biocontrols, recommended. One rule-of-thumb to consider: the bigger the container or release site the longer the interval between releases can potentially be (and thus fewer releases); and the opposite is true for smaller containers or growing areas.