Hypoaspis-A (Hypoaspis aculeifer) - Bulb mite and thrips predator
Target pests: Bulb mites, Rhizoglyphus robini and R. echinopus; bulb scale mite, Steneotarsonemus laticeps; thrips larvae (soil-pupating 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); fungus gnats, Bradysia spp.
Hypoaspis aculeifer is a soil-dwelling mite found in Europe, Asia and North America. It was also discovered in Queensland in stone fruit orchards, the origin of this culture. It is predaceous on a broad range of soil organisms, including bulb mites, thrips, fungus gnats, and nematodes. It is generally used against bulb mites, Rhizoglyphus spp., and recently has shown promise against thrips at ground level in flower crops such as roses and gerberas, in combination with above ground applications of cucmeris.
Hypoaspis-A is supplied in a peat and vermiculite medium in quantities of 15,000/litre containing all stages of the mites.
Life history and biology
Hypoaspis aculeifer is a small, 1 mm-long, soil-dwelling mite, similar in appearance to Hypoaspis-M, but slightly smaller with more robust, spiny, darker brown rear legs, a rounded rear edge to the dorsal shield, and shorter mouth parts. The dorsal shield is shinier, more rounded and less hairy than Hypoaspis-M. It has three immature stages: a whitish six-legged larva and two 8-legged, pale brown nymphal stages. Males are much smaller than females and slightly less common. Nymphs and adults feed on a variety of soil organisms, including nematodes, springtails, fungus gnat larvae, root aphids, mites and thrips larvae, preferring moist habitats high in organic material. Hypoaspis-A has been particularly useful for control of bulb mites. The development rate is similar to that of bulb mites-taking about 40 days to complete development at a cool 16°C, but only 12 days at 27°C. It can survive for long periods by scavenging. Females each lay 3-4 eggs per day under ideal conditions. Consumption of thrips larvae is higher than that of Hypoaspis-M in laboratory trials, but this may be influenced by alternative food and adaptability under greenhouse conditions. Hypoaspis-A is able to penetrate soils to a greater depth than Hypoaspis-M allowing it to reach and inhabit bulbs where pest mites live and breed.
Hypoaspis-A is used against bulb mites in bulbous crops such as lilliums and freesia. It may also be used in various crops attacked by fungus gnats or by ground-pupating thrips species such as western flower thrips, onion thrips, plague thrips and melon thrips. For bulbs, predators may be used in both storage and propagation phases.
Reported optimal temperature conditions vary, from 18-23°C (UK) to 25-30°C (Japan). Variation may be due to strain differences. Temperatures much greater than 30°C are harmful, but tolerance of low temperature is reportedly greater than for Hypoaspis-M, with good activity at 10°C. 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.
Storage and handling: Hypoaspis-A should be distributed soon after receipt. They may be stored at 12-18°C for a short period in the dark, but do not refrigerate below 10°C.
Release method(s): Rotate the container of Hypoaspis-A thoroughly prior to, and during release to ensure mites are evenly distributed through the carrier. Sprinkle material on the top of the substrate or bulb scales by hand or scoop. 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 bulbs and corms in storage, it is best to apply preventatively. When bulbs are being planted into soil that has previously been used apply predators at, or immediately after planting. For new crops in clean media, Hypoaspis-A should be released 1-2 weeks after planting. Make a repeat application after 2-3 weeks to ensure establishment. Mites may be released into existing plantings or pre-used media at any time. More than one application at 2-3 week intervals is advisable, until well established.
Release rates: For bulbs and corms, apply 10 predators/100 bulb scales (preventative) or 20-100 predators/100 bulb scales (curative). For crops, apply 100 predatory mites/m2 (preventative), and repeat after 1-2 weeks, or apply 200-500 predatory mites/m2 (curative) and repeat as necessary. Contact Biological Services for crop specific suggestions as experience with this product is limited compared with Hypoaspis-M.
Monitoring control success
Bulbs: leave some areas untreated and compare infestation levels of bulb mites. Examine for presence of Hypoaspis-A and pest mites by destructive sampling some of the bulbs from treated and untreated areas under a 10 x magnification.
Other crops: Hang yellow sticky cards in the crop canopy and monitor weekly for adult thrips and fungus gnats. A slow but steady decline in numbers should occur after 2-3 weeks. Be aware that thrips are highly mobile and may invade from outside the greenhouse. Check the upper few centimetres of the growing mix periodically for Hypoaspis aculeifer, using a 10x hand-lens. Sprinkle media onto a white surface to detect them more easily. This predator like to burrow and will not appear on the surface when media is vibrated, tapped or blown on like Hypoaspis-M.
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, introducing lower numbers regularly until established. For bulbous crops, it may be advisable to use a hot water treatment on the scales prior to planting out to reduce Rhizoglyphus to low numbers prior to releasing Hypoaspis-A. In greenhouses without climate control, mites may be killed by very low (<5°C) and very high (>32°C) temperatures. Other, less effective soil mites similar in appearance to Hypoaspis-A 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. Where Hypoaspis-A are used predominantly for fungus gnat contol they may be combined with additional treatments such as entomopathogenic nematodes (Steinernema feltiae) or Vectobac® (Bacillus thuringiensis israeliensis) for a faster knock-down of fungus gnats.
Check on receipt that Hypoaspis-A are active by sprinkling mix onto a white surface (temperature should be >20°C) and observing with a 10x hand-lens. Mites leave the production unit alive and in good condition, but delays in transit or extreme temperatures may harm them. Biological Services need to be informed if there are problems in shipment.
Hypoaspis-A 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-A. Some media-applied pesticides such as Pirimor® are safe in substrates with a high content of organic matter because of adsorption of the pesticide, but may be harmful in rockwool, vermiculite and perlite.