Bringing the idea of top layers for supporting predatory mites into practice: experiences from various greenhouse cropping systems

Abstract: Top layers that provide food sources for astigmatic prey mites can support soil-dwelling predatory mites, but also phytoseiid predatory mites on plants that are able to migrate between the plant and soil. Small scale experiments have proven that such top layers can increase predatory mite densities and enhance biological control of pests. Here we present results of the application of top layers in practice in different greenhouse crops: alstroemeria, chrysanthemum and roses. In all these crops we were testing whether the application of a top layer could enhance the control of western flower thrips, Frankliniella occidentalis (Pergande), which is a major pest in greenhouse ornamental crops. The top layers gave good results in some cases, but in other cases the effects were very limited. Possible reasons for the varying results could be 1) predator satiation effects, 2) prey preference of the predator, 3) intraguild predation 4) negative characteristics of the host plant and 4) the pupation behaviour of thrips. The possibilities and constraints of applying top layers in practice will be discussed.Extended abstract