Introduction methods

This page describes the various introduction methods. Consult the 'Crops' page for information specific to your crop.


Amblyseius swirskii is supplied in shaker cans, mixed with bran. There are cans available with different contents and numbers of predatory mites. The shakers are primarily intended for light curative introductions (if whitefly or thrips are present). In crops with sufficient pollen, such as sweet pepper and aubergine, the predatory mites in shakers can be released preventatively once the crop is flowering. The product is also used in cans to be applied by means of a blower (see below).

Slow-release bags

Just as in the case of the predatory mite Amblyseius cucumeris, slow-release bags have also been developed for A. swirskii.  This bags produce large numbers of predatory mites over a period of 4-6 weeks and can be simply hung up in the crop using hooks.

Advantages of slow-release bags

The advantages of the slow-release bags are summarised below:

  • Predatory mites can also be released preventatively in crops without pollen
  • Fast growth of the population of predatory mites- A large number of predatory mites are released into the crop over a period of 4-6 weeks
  • Buffering effect: the steady release of predatory mites cushions the negative effects of any chemical residues present. The mites can therefore be released sooner than when using shaker cans.
  • If flowering in crops like sweet pepper temporarily ceases, resulting in less pollen available as food, the bags will still continue to produce enough predatory mites under these less favourable conditions.
  • Easy to set out and ensures an appropriate and even distribution of the predatory mites throughout the crop.


In crops such as chrysanthemums, roses and gerberas, the use of biological pest control is tricky and time-consuming. However, a great deal of time can be saved with an automatic blower. Simply by putting the natural enemies into the reservoirs and switching on the machine, the natural enemies are distributed quickly and evenly over the crop.
(link to film clip
 Once released using the blower, the predatory mites get straight to work. With this process, no bags or other packaging are left behind in the crop.

Alternative introduction methods

Natural enemies can be introduced into the crop in a number of different ways. Predatory mites can be shaken or blown directly into the crop, or introduced as cultures in little bags hung onto the plants. Two alternative introduction methods are described below. The first is introduction by means of banker plants and the second is introduction through the overlaying of leaves. These methods are however rarely applied in practice.

A banker plant for Amblyseius swirskii

Banker plants are living plants intended as a kind of launch pad for natural enemies in a productive crop. The castor oil plant Ricinus communis (Euphorbiaceae) is ideal as a banker plant for various predatory mites. The plant is a wind pollinator and continually produces large quantities of pollen (see photo of flowering). Besides pollen, the plant also produces extrafloral nectar, released from glands on the tips of the leaves and by the stem. Both the pollen and the nectar form a source of nutrients for predatory mites. By placing a flowering castor oil plant amid the crop (see photo), there is constantly food available for predatory mites, and they can therefore build up their population in periods without prey as well. This is of particular interest in crops without pollen (such as cucumbers and ornamental crops). The castor oil plants can also serve as a bridging solution during crop rotations.

Leaf-overlaying during crop rotation

In the cultivation of fruiting vegetables under glass, it is customary to thoroughly clean the greenhouse after every crop and to start again with young plants in a spotless environment. This is done in order to minimise the risks of diseases and infestations being carried over to the next crop. However, such working methods also automatically result in the removal and destruction of the built-up populations of natural enemies. WUR Greenhouse Horticulture investigated the possibilities for carrying natural enemies over from the old crop into the new crop. The greatest gain is to be achieved in crops such as cucumbers, since there the crops follow on from each other in rapid succession and there is little time for a building-up period for the natural enemies.

Research carried out by WUR Greenhouse Horticulture has revealed that it is perfectly possible to maintain a population of predatory mites during the period of a number of successive crops without having to reintroduce them each time. This could be achieved by keeping cool leaves or flowers from the old crop during the crop rotation for a week and then overlaying them onto the young plants in the new crop (see photo). Cucumber leaves can be overlaid at the end of a crop cultivation period. An even better option is to do this as soon as the population of predatory mites has reached a high level. Laying out leaves at an earlier stage is only possible in enterprises with several cucumber crops with different cultivation periods. The following must be taken into account regarding the method of leaf-overlaying:

  • select relatively young leaves, free of disease and infestation
  • the best results are achieved by picking the leaves at the point at which there is a high density of predatory mites present (at least 20 predatory mites per leaf).
  • Cucumber leaves with predatory mites can best be kept in a plastic bag at 7ºC for a maximum of one week