Spider mite control

How does it work?

Amblyseius (Neoseiulus) californicus is an active predatory mite that has specialised in feeding on mites in the family Tetranychidae. This includes the common Red Spider Mite or Two-Spot Mite Tetranychus urticae, and the Carmine Mite Tetranychus cinnabarinus. It is less specialised than Phytoseiulus persimilis, and while it prefers to feed on spider mites, it can feed and reproduce on other arthropod prey or pollen. Where few spider mites are present, it is able to survive by feeding on these alternative sources of food, and so can persist in a crop longer than Phytoseiulus persimilis.

Like P. persimilis, it lays eggs in spider mite colonies, and these hatch to produce a six legged larva followed by protonymphal and deutonymphal stages before adulthood. Total development time at 21°C is nearly 10 days, while at 30°C this reduces to 5 days. These figures compare favourably with those for the principal prey Tetranychus urticae, which develops at 16 and 7 days at these temperatures respectively.

Each female is reported to lay an average of 3.85 eggs per day when feeding on Tetranychus urticae, 1.12 per day on Frankliniella occidentalis, and 1.18 per day on corn pollen (Croft, Monetti and Pratt, 1998). The lifetime total per female is reported to be higher than that for P. persimilis, but there are only two females to every male, rather than 4 females to every male for P. persimilis. Overall egg production by a population will therefore be lower than for P. persimilis.

Laboratory studies, and field studies on strawberries in California, seem to show that Amblyseius californicus is a much less effective predator than Phytoseiulus persimilis. It lays fewer eggs, does not search for prey so thoroughly, eats fewer prey individuals and has a lower rate of population growth. Nevertheless it is regularly found in the same fields as P. persimilis, and is reported from various glasshouse and field crops to persist for longer and to control spider mites in situations where P persimilis does not work well. These include hot, dry conditions and ornamental plants where the density of spider mite is low. It is possible that the ability to subsist on other sources of food allows A. californicus to survive for longer and continue searching in situations where P. persimilis would starve to death.

Amblyseius californicus is also reported to be highly resistant to some commonly used insecticides. In crops in Spain, where there is a history of pesticide use, Amblyseius californicus is often the first predator to return to a crop after treatment.

When and where should you use it?

Amblyseius californicus can be used in any situation in which Phytoseiulus persimilis would be used. It is normally recommended for use in conjunction with P. persimilis, or in areas of the crop where P. persimilis has previously failed because of hot dry conditions. On specific crops it may be recommended alone, where trials have shown it to be effective.

How should you use it?

Amblyseius californicus is supplied as units of 2,000 mites mixed with an inert carrier material in 100 cm³ vials. Where spider mite infestation is low, a rate of 4/m² applied over two weeks should be sufficient. On identified colonies or larger areas of infestation apply at a higher rate to gain control, or use a compatible acaricide to reduce spider mite populations prior to release. On receipt of the mites, keep the vials cool and horizontal until ready to use them. Immediately before use, tap the vial to dislodge the mites from the inner surface, and rotate it gently to mix the mites uniformly into the carrier. Remove the cap and tap small numbers of mites onto the surface of spider mite infested leaves. Make sure you distribute some mites into the areas around the outbreaks. If this is not done, the predators may remain in areas of plentiful food, and not migrate to the edge of an infestation. Surviving mites at the periphery then continue to breed unchecked and the colony may expand in a ring away from the areas with predators.

When should you not use it, and what are the alternatives?

Amblyseius californicus is more expensive than Phytoseiulus persimilis, and is not recommended for use in crops where the latter predator has previously given good control. It should not be used as the sole means of control where there are heavy outbreaks of spider mite. Use a compatible acaricide such as fenbutatin oxide or hexithiazox to reduce spider mite numbers before releasing predators in this situation.

Note also that Amblyseius californicus is not native in the United Kingdom, and may be released only in glasshouses, under licence from DEFRA. Restrictions apply concerning the types of crop and areas of crop on which it may be released. Consult your supplier for the latest information.

What will it do?

Amblyseius californicus will control outbreaks of spider mite when used as directed. It should always be used preventively, while spider mite populations are small.

What will it not do, and what are the control options?

Amblyseius californicus will not control large outbreaks of spider mite except at high release rates. Use a compatible chemical in this situation. Amblyseius californicus feeds on a wider range of prey than P. persimilis does and there is evidence that it will control other mite pests such as Tarsonemid Mites). It is recorded from fruit trees infested with the European Red Mite Panonychus ulmi, and may contribute to the control of this pest.

Chemical compatibility

There are a number of acaricides that are compatible with use of Amblyseius californicus. Examples are fenbutatin oxide, hexithiazox and bifenazate. Dried residues of abamectin are not directly toxic. This compound is useful for cleanup treatments early in the growth of the crop or towards the end of the crop cycle.

There are indications that regular use of elemental sulphur as a fumigant against powdery mildew and other diseases causes serious suppression of populations of Phytoseiid mites, and can lead to outbreaks of spider mite. Reducing the frequency of use and ensuring that Phytoseiulus or Amblyseius californicus are established before first use may limit this suppression.