Persimilis is a voracious feeder on all stages of two-spotted mite, a major pest of many crops. It is one of the world’s most commonly reared natural enemies and has been produced commercially in Australia for over 25 years. This beneficial mite has been used successfully in many situations including strawberries, greenhouse crops and deciduous fruits. The adult predatory mite is orange, while the younger stages are clear.
Both forms are pear-shaped and fast-moving. Persimilis eggs are oval, tinged with orange and twice the size of spider mite eggs. Adult persimilis feed on two-spotted mite eggs, young and adults. Even though persimilis are only slightly larger than the mites on which they feed, an adult can destroy twenty young or seven adult two-spotted mites per day. Juvenile stages of persimilis feed on eggs and larvae of spider mites. At a temperature of 25°C, the predatory mites multiply twice as fast as their prey.
- Two-spotted mite Tetranychus urticae
- Bean spider mite Tetranychus ludeni
Pests controlled by persimilis include two-spotted mite, the major target pest, and the less important bean red spider mite. Both belong to a group of eight-legged, plant- feeding mites called spider mites. Two-spotted mite is a major pest of many crops in a range of climates.
Two-spotted mites are usually pale green with two dark patches on their back. In cold weather, however, they may turn red.
The adults are about 0.5 mm in length and are best viewed with a hand lens. Their eggs are round and pearly white.
Two-spotted mites prefer the underside of leaves. They suck out the leaf cells, causing minute yellowish feeding marks that may join together, causing leaves to shrivel and die. This pest is difficult to control by chemical means because of its short life cycle and resistance to chemicals. It is also difficult to obtain good spray coverage on many crops.
Persimilis does well in humid areas and in crops with heavy foliage. It has been used successfully in many crops, including papaws, strawberries, cut flowers, hops, raspberries, capsicum, eggplant, tomatoes, greenhouse vegetables, ornamentals, blackcurrants, pome fruit, stone fruit and grapes, as well as in field crops such as corn and soybeans.
Chemical residues toxic to predatory mites must have time to degrade before persimilis are released. Synthetic pyrethroids and some organophosphates may need up to eight weeks to break down.
There is a range of less hazardous chemicals which are preferred if spraying is necessary. Contact suppliers for detailed information on the toxicity of chemical residues.
Inspect crops regularly for the presence of mites, especially on the windward side, in dry spots and at edges. Introduce predators while infestation of two-spotted mite is still in its early stages. For instance, in strawberries, predators should be introduced when four out of thirty full leaves have mites present.
Check the surrounding vegetation for sources of spider mite and treat these areas as well. If a hot spot is detected early and treated quickly, the predators will move from that spot and follow the mites as they spread. Details of the best timing and method of release for various crops are available from suppliers.
If overhead irrigation is required it should be applied before introducing predators rather than shortly after. Likewise, if it is raining or rain seems imminent, delay release until the plants are dry. Predators can be stored at 7 – 10°C for up to seven days.
Persimilis are despatched on bean leaves in packs of 10 000. These include persimilis adults, nymphs and eggs, plus small numbers of two-spotted mites as food for the persimilis. Each pack contains over 300 individual leaves. Place these leaves into the foliage of the infested plants.
Recommended release rates
- Field crops: minimum one pack of 10,000 mites per 1,000 – 2,000 m2.
- Strawberries: minimum one pack of 10,000 mites per 3,000 – 5,000 plants.
- Ornamentals and cut flowers: minimum one pack of 10,000 mites per 200 – 500 m2.
Calculate how many bean leaves carrying persimilis are available for the crop area and distribute the leaves evenly through the infested areas. It is important to place extra bean leaves in heavily infested areas. Gently separate the bean leaves carrying persimilis and tuck them into the foliage at the level of the two-spotted mite infestation and where they will be protected from direct sun. If there are any extra leaves, re-treat those areas with highest pest numbers.
A note on release rates: Unlike chemicals which generally exhibit a clearly defined dose response curve, with beneficial insects, more is always better. However, they are costly to produce and the goal should be to achieve the best results at minimal cost. We are constantly trying to strike a balance between cost and efficacy. There are many factors that should be considered including the value of the crop, the magnitude of the pest population and the activity (or otherwise) of naturally occurring beneficial species. Also unlike chemicals, where it is common to respond to pest populations that have already exceeded some ‘economic threshold’, we recommend establishing beneficials early in the life of the crop before pest populations reach threatening levels. In most cases our releases are inoculative and we anticipate that our beneficials will establish and breed up within the crop to give long term control. As a general principle, 2-3 releases of modest numbers is better than a single large release – this reduces risk, improves establishment and accelerates the development of multiple overlapping generations of the beneficial species.
Persimilis will be difficult to find for a week or so after introduction. They disperse quickly in search of food. Mark a few places where predatory mites were released, especially those with good numbers of spider mites. These sites can be regularly checked to assess spider mite numbers as well as establishment of predatory mites. Expect spider mite numbers to keep increasing at first.
Reinfestations by spider mites can occur, especially in greenhouse crops.
Predatory mites may still be present in low numbers and may increase to quell the outbreak, often unnoticed by the grower.
Regular checks should be maintained to assess the presence or absence of both spider mites and predators.
Many cut-flower growers and nurseries have adopted the regular release (dribble) method of introducing predators. This ensures that there are always predators present to move into any new mite infestations.
Cultural practices to aid establishment
Persimilis thrives in warm to hot, humid conditions, whereas two-spotted mite does best in very hot, dry conditions. Plants close together or with dense foliage will automatically provide a microclimate favourable to predators.
Plants or varieties with a more open habit or plants exposed to wind are less favoured by predators. Such areas should be checked regularly for mites, especially during hot, dry conditions. Some overhead watering will improve the environment for predators during dry periods.
Care should be taken with the use of chemicals. All insecticides should be avoided until two weeks after releasing persimilis.
Fungicides (except Benlate, Morestan and Afugan) generally have low toxicity to persimilis.
Persimilis are usually found under the lower leaves where two-spotted mites gather, so if sprays of low to moderate toxicity are applied to the upper foliage, predators may not be greatly affected.
If, despite releasing persimilis, two-spotted mite increases to damaging proportions, a compatible miticide can be applied to reduce mite numbers. This will allow the predators to catch up and eliminate the remaining mites. Spot spraying is preferable to blanket spraying. Fenbutatin oxide (Torque), hexythiazox (Calibre) and propargite (Omite) are the safest miticides to use with persimilis.
Persimilis is not suitable for controlling mites in tree crops in dry climates. The mite typhlodromus is suitable for such conditions.
Other natural enemies of two-spotted mite
- Black ladybird Stethorus fenestralis
- Native predatory mites Amblyseius spp
- Predatory mite Typhlodromus occidentalis
- Predatory thrips Scolothrips sexmaculatus
- Ladybird beetles Coccinella repanda and Harmonia conformis
- Hoverfly larvae Syrphus spp