Thrips is a major problem in ornamental plants production. Experiments of Wageningen UR Greenhouse Horticulture were conducted to see how the predatory leaf mite N. cucumeris can be supported.
A layer on top of the soil with a population of the suportive mite Tyrophagus putrescentiae could help the predatory mite to survive periods with little pest (thrips). The colonization of the toplayer by the supportive mite was investigated wth toplayers of different materials like bran, wheat middlings, corn gluten, and several compost types. The best result was achieved with bran in combination with baker's yeast.
Questions before application on a practical scale included humidity requirements, and the density of the top layer. Tyrophagus putrescentiae seems to like high RH, but it certainly can’t coop with drought! The lower RH limit lies somewhere between 55 and 75% RH. Local application of the top layer is less effective as it does not contribute to N. cucumeris to spread throughout the crop.
A practical test in a newly planted Alstroemeria crop with a full-field bran and yeast top layer was set up to study the long term survival of the mites and the effects on thrips control. Meanwhile, other soil predatory mites have been attracted by the top layer.
The research on top layers for Alstroemeria is part of the 'Masterplan Trips', a Public Private Cooperation (top sector T&U and various agricultural cooperatives).