Combating which infestations?
Amblyseius swirskii is a polyphagic predator with many different types of prey on its menu. In sweet peppers, aubergines and gerbera crops, A. swirskii can also survive on pollen. However, it is not yet clear whether this applies to pollen from all types of crop. If thrips or whitefly are present, the predatory mite quickly grows in numbers.
Thrips
Amblyseius swirskii eats the first larval phase of thrips. A female mite can consume up to five young thrips larvae per day at 25°C. This is comparable with the predation capacity of A. cucumeris in the laboratory.
A. swirskii can develop on plants much more quickly than A. cucumeris if prey is available. This has emerged from trials carried out by both WUR Greenhouse Horticulture and Koppert. Over a period of three weeks, the predatory mite population of A. swirskii grew nine times faster than that of A. cucumeris in cucumber crops. This makes this predatory mite much more effective in combating thrips than A. cucumeris. Depending on the crop, other natural enemies of thrips besides A. swirskii are also necessary in order to guarantee good control.
Whitefly
A. swirskii mainly eats the eggs and the initial larvae of both glasshouse whitefly and cotton whitefly. Each female mite can consume up to 19 eggs or 15 young larvae per day at 25°C. There are also indications that A. swirskii eats the eggs of the cabbage whitefly.
Depending on the crop, other natural enemies of whitefly besides
A. swirskii are also necessary in order to guarantee good control.
Spider mite
A. swirskii also eats the younger phases of two-spotted spider mite and has a slightly suppressive effect on two-spotted spider mite. The predatory mites are hindered by the spider mite webs, and consequently avoid spider mite hot-spots. For effective control, it is absolutely essential to release specialised natural enemies of spider mite.
Tarsonemid mites
It is known that A. swirskii also eats broad mite. Other predatory mites that can help to control broad mite include Amblyseius californicus, Amblyseius cucumeris and Amblyseius barkeri.
Is there a preference?
In a greenhouse situation, it is not unusual for several infestations to be present at the same time. A polyphagic predator like A. swirskii can therefore choose from various food sources such as thrips larvae, eggs and the larvae of whitefly, spider mite and pollen from the plant. You may wonder whether this is a disadvantage in combating a particular infestation. Does A. swirskii have a clear preference for a particular infestation or source of food?
Experiments carried out at the University of Amsterdam showed that whitefly was controlled better when pollen was also available than when only whitefly was present. Greenhouse trials by WUR Greenhouse Horticulture demonstrated a similar principle. The control of glasshouse whitefly was better when both thrips and glasshouse whitefly were present than when only glasshouse whitefly was present (see figure 1). The control of thrips was equally good in both cases. A varied menu does not therefore lead to a certain type of prey being ignored. Instead, it results in much stronger growth in the population and thus in better control of the pests present (see figure 2).
Figure 1. Development of A. swirskii in the presence of thrips, glasshouse whitefly or a combination of the two over a period of 10 weeks after the release of the predatory mites.
Figure 2. Development of glasshouse whitefly in a cucumber crop with A. swirskii in a situation with only glasshouse whitefly or a situation with both glasshouse whitefly and thrips.
Development of glasshouse whitefly in a cucumber crop A. swirskii in a situation with only glasshouse whitefly or a situation with both glasshouse whitefly and thrips.