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Hypoaspis-M (Stratiolaelaps scimitus, formerly known as Hypoaspis miles) - Fungus gnat larval predator

Target pests: Fungus gnat larvae (mostly small larvae), Bradysia spp.; thrips larvae and pupae at ground level, including western flower thrips, Frankliniella occidentalis, onion thrips, Thrips tabaci, plague thrips, Thrips imaginis, and melon thrips, Thrips palmi; soil mealybugs.

Hypoaspis-M

Stratiolaelaps scimitus is a soil-dwelling mite predaceous on a variety of soil organisms, but is particularly useful against fungus gnat larvae. In combination with other above ground predators it is useful in the control of various thrip species that pupae in the soil. It is widely distributed naturally in many countries, including Australia, and has been in commercial use for over 15 years. this predator has also proved useful in controlling pest mites in reptile enclosures, and spider colonies.

Hypoaspis-M is packaged in a pasteurised peat and vermiculite mix and sold by the litre in punnets or bags. Each litre contains at least 15,000 mites of all mobile stages. A harmless bran mite may be present as food in transit. This predator is not effective against shore fly larvae, which are semi-aquatic.

Life history and biology

Hypoaspis-M life cycle
Click to enlarge life cycle

Stratiolaelaps scimitus is a small brown mite ~1mm long, with a distinctive darker brown V-shaped marking on the upper surface of the body. It inhabits the upper levels of the growing media particularly loose open substrates and prefers media high in organic matter such as peat, sawdust and coconut fibre, but will also establish in rockwool, and scoria. Oval eggs are laid into the media, which hatch into 6-legged white larvae, which then pass through two 8-legged, brown nymphal stages before reaching maturity. Female mites lay 2-3 eggs per day and consume 1-5 prey per day. Males are much smaller than females but are in equal numbers. The length of the life cycle from egg to adult varies with temperature and with food supply. It takes about 17-18 days to reach maturity at 20°C and 10-13 days at 25°C. At 15°C this may be extended to >30 days. While adults can live for several months without target hosts as food, this is probably temperature-dependent and mites may be sustaining themselves on nematodes and soil microorganisms or scavenging on plant debris. They do not feed on plants. While they are found below ground level during the day, there have been reports of them climbing into foliage at night to feed on mealybugs and other organisms, at the base of plants or low down in crowns or lower leaves. All stages and both sexes are predatory.

Crop usage

Hypoaspis-M is suitable for use in all crops infested with fungus gnats, including bedding plants, seedlings, propagation beds, and vegetable and ornamental crops whether in pots, bags or beds. Hypoaspis-M also provides supplementary control of larvae of those thrips species which drop to the ground to pupate, including onion thrips, western flower thrips, plague thrips and melon thrips, complementing the use of Cucumeris on foliage.

Environmental preferences

Optimum temperature range is 20-30°C. Temperatures much less than 10°C and greater than 32°C are harmful, so greenhouses without environmental controls will need to re-introduce mites if the media temperature falls outside this range. To some extent, media is buffered from the broader range of temperatures experienced within the crop canopy. Mites prefer moist conditions which support the soil organisms on which they feed, but they do not like water-logged conditions.

Application information

Storage and handling: Hypoaspis-M should be distributed soon after receipt. They may be stored at 15-20°C for a short period in the dark, but do not refrigerate below 10°C.

Release method(s): Rotate the container of Hypoaspis-M thoroughly, prior to before and during release to ensure mites are evenly distributed through the carrier. Sprinkle material on the top of the substrate by hand or scoop. Mites can reach high densities after a few weeks. They appear to tolerate such concentrations without becoming cannibalistic, as long as food is plentiful. Discontinuous surfaces such as pots and bags should be treated individually as mites may not disperse to untreated units. Moist soil under benches should also be treated.

Timing of application: For new crops in clean media, Hypoaspis-M should be released 1-2 weeks after planting. The delayed timing will allow any fungus gnat eggs to hatch into larvae. Make a repeat application after 2-3 weeks to ensure more even establishment. Mites may be released into existing plantings or pre-used media at any time. More than one application is advisable at 2-3 week intervals until well established. Note that adult flies are not controlled and will continue to lay eggs until their life span of a few weeks is completed. Combine Hypoaspis-M with additional treatments such as entomopathogenic nematodes (Steinernema feltiae) or Vectobac® (Bacillus thuringiensis israeliensis) for a faster knock-down.

Release rates: Apply 50-400 mites/m2 depending on infestation level. Use higher rates where organic substrates such as cocopeat, sawdust or composted bark is used as the growing medium as these favour fungus gnat development especially when fresh.

Preventative: each litre will treat 100-150m2 of bedding plants, or 200 to 300 pots (150 mm).

Curative: Increase release rates to 200-400 mites/m2 if fungus gnats are already noticeably present. Continue releases every 2-3 weeks until yellow sticky cards hung in the lower crop canopy catch on average fewer than 50 adult fungus gnats per card per week, or 20 per card in the upper canopy.

Monitoring control success

Hang yellow sticky cards in the lower crop canopy and monitor weekly for adult fungus gnats. A slow but steady decline in fly numbers should occur after 2-3 weeks. Once mites have established, tapping/vibrating the side of pots and bags or blowing onto the soil will often bring them to the surface for visual confirmation of their presence, or sprinkle media onto white card and examine for mites.

Tips for best results

Apply within 24 hours of arrival, but avoid stressing mites by keeping them at 15-25°C during distribution. Apply to the surface of the media: do not mix into potting media. Apply to all pots and bags. Use preventatively, particularly for seedlings and cuttings. In greenhouses without climate control, mites may be killed by exposure to very low (<10°C) and very high (>35°C) temperatures. Other, less effective soil mites similar in appearance to Hypoaspis-M may tolerate these conditions and it may appear that the correct mite is still present. If in doubt, collect mites and send them to Biological Services for identification.

Quality control

Check on receipt that Hypoaspis-M are active by sprinkling mix on a white surface (temperature should be >20°C) and observing with a 10x hand-lens, or tapping the bag or container to bring mites to the surface. Mites leave the production unit alive and in good condition and generally very hardy, but delays in transit or extreme temperatures may harm them. Biological Services needs to be informed if there are problems in shipment.

Pesticide compatibility

Hypoaspis-M is relatively protected from contact with foliar-applied pesticides, but may be affected by run-off. Synthetic pyrethroids such as bifenthrin (Talstar®) or permethrin (Ambush®) have long-term negative effects. Check side-effects charts carefully and avoid using pesticides that are known to be harmful to Hypoaspis-M. Some media-applied pesticides such as pirimicarb (Pirimor®) can be safe in substrates with a high content of organic matter because of adsorption of the pesticide, but have been shown to be harmful in rockwool, vermiculite and perlite.

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Technical resources

Hypoaspis technical sheet (176 kb)