This predatory mite was long known as Hypoaspis miles, but recent taxonomic changes have renamed it Stratiolaelaps scimitus. However, the name Hypoaspis miles remains preferred and more widely used among biological control experts.
In the wild, the Hypoaspis feeds on various soil insects and their larvae. It's of interest in agriculture because its prey includes larvae of fungus gnats, shore flies, thrips, and also soil aphids.
This predator, with a size of up to 1mm, has a brown body color. It inhabits the topsoil layer (up to 4 cm deep) in natural conditions and can also be found on plant residues. In production settings, it also navigates artificial substrates and surfaces of pots, shelves, and similar structures.
Egg-laying occurs in moist soil, peat, or organic residues. Hence, having such a substrate in a production area is crucial if a farmer intends to establish a long-term and stable population of this predator.
Population growth rate depends on temperature. Below 10°C, the mite's development halts. At 15°C, it extends to up to 5 weeks, while at 24°C, the life cycle shortens to 2 weeks. However, temperatures of 32°C and above stymie population growth.
During its growth, the predator goes through three nymphal stages. After egg-laying at a standard temperature of 20°C, first-stage larvae emerge in 6 days. A few days later, the second stage, the protonymph, appears, followed by the third stage, the deutonymph. This span takes about 10 days, during which the young mites actively feed. At 20°C, the overall development period from egg to adult is around 17-18 days, given enough prey.
An adult Hypoaspis can eliminate up to 8 first-stage sciarid larvae daily. However, its efficiency drops when hunting older larval stages, managing to attack no more than one fourth-stage larva per day.
A significant feature of the Hypoaspis is its ability to target thrips larvae that fall onto the substrate for pupation, including the Western flower thrips (Frankliniella occidentalis). However, thrips control is multifaceted, and Hypoaspis is just one tool in this fight. It complements other biological control agents against thrips, such as parasitic nematodes.
Since most pesticides target plant biomass and the Hypoaspis resides in the substrate, its contact with these chemicals is minimal. This property allows its use alongside many chemical protection agents, though it's incompatible with soil treatments.
Application rates for Hypoaspis are broad, ranging from 100 to 1000 individuals/m², depending on the pest situation on crops.
The standard preventive dosage is 50-100 individuals/m². In the presence of thrips or other pests, the release rate is 250-300 individuals/m². For high pest populations, the rate might go up to 500-1000 individuals/m².
It's best to introduce the predator preventatively or when pest populations are low. They are introduced to the substrate, compost, or directly on mineral wool cubes, where they immediately begin foraging. If there are open soil areas or other substrates beneath the shelves, these should also be inoculated with the predator as pests might inhabit them.
Hypoaspis's population stability is due to its longevity, which can last several months. Even without food, these mites can survive up to 7 weeks. This makes them suitable for long-term crops like ornamental plants.
Hypoaspis-based products have a short shelf life, usually not more than 48 hours post-receipt, stored at 12-18°C. Being a moisture-loving mite, to prevent the carrier from drying out, it should be kept at elevated humidity.
Recently, there have been attempts to use Hypoaspis in beekeeping against honey bee parasites - the Varroa mites. In essence, the potential of this predator remains untapped, and further innovations will reveal new applications for it.
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