Science - February 3, 2005

Banker plant hosts mites in greenhouse

A new Mediterranean predatory mite will be used to protect cucumbers and peppers growing in greenhouses against thrips and whitefly. The Greenhouse Horticultural Research Unit of Applied Plant Research (PPO) selected the promising mite Typhlodromips swirskii, and plan to keep it year-round in greenhouses by using the castor oil plant as host.

‘The predatory mite came out as one of the top ten in the comparative tests we did, as it destroys both thrips and whitefly. Most natural enemies concentrate on only one victim,’ says Gerben Messelink one of the PPO researchers at the Greenhouse sector in Naaldwijk.

The predatory mite, which comes from the Mediterranean area, does well in the warm climate of the greenhouse and large populations can be grown in a short time. An important advantage is that the mite can easily be fed when crops are not being grown by putting castor oil plants in the greenhouse. If looked after well, the plants produce large amounts of pollen throughout the year, enabling the mite to survive in times of fewer whitefly and thrips. Using the castor oil plant as a banker plant in this way means that the grower does not have to keep ordering new supplies of predatory mites.

Thrips and whitefly are both feared pests in greenhouse cultivation. Thrips attack the flowers and interfere with fruit setting, resulting in bent cucumbers that cannot be sold and damaged sweet peppers. Whitefly feed on the sap of greenhouse plants and dirty the leaves with the sticky honeydew that they deposit. As a result, crops produce less and are more susceptible to fungi. The predatory mite sucks the eggs and larva of these insect pests empty, thus preventing them from spreading.

PPO will track the predatory mites’ performance in the greenhouse this season. ‘We are curious to see whether the mite will live up to its promise in real-life conditions,’ comments Messelink. The project is supported by the Horticultural Product Board and the Ministry of Agriculture. / GvM

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