More than 7 billion predatory mites were released in greenhouses in the Netherlands in 2004 as a means to combat thrips. This is 30 percent more than in 2000. The rise is not a result of an increase in the area treated, but of higher dosage rates.
Biological pest control
More than 20 species were used for biological pest control in glasshouse culture in 2004, including ten species of ichneumon wasp and six species of predatory mite. The main pests combated organically are thrips, red spider mite, greenhouse whitefly and aphids.
In terms of numbers, biological pest control is being increasingly dominated by predatory mite used against thrips.
The thrips is a small slender-bodied insect which feeds on plant sap. Under favourable conditions, it will easily multiply and become a pest.
In 2004 more than 70 percent of all total predatory mites used to combat thrips were used in the cultivation of greenhouse vegetables, and nearly 30 percent in the cultivation of flowers in greenhouses. Half are used on cucumbers.
Distribution of total predatory mites used against thrips in greenhouse culture in 2004 (%)
Almost all of the increase in the number of predatory mite used against thrips in greenhouse culture was the result of higher dosage rates. The relative area on which the mites are used has become smaller in recent years. The decisive factor is the increased dosage in cucumber cultivation.
In the last ten years the annual dose of predatory mite used against thrips in cucumber cultivation has increased almost fourfold. Not only are more mites used more frequently for each crop, the number of crops has also increased from two to three per year. For flowering plants, too, the dose has increased, although the area treated has decreased. For gerberas en roses the dose has decreased on the other hand.
Number of predatory mites used against thrips in greenhouse culture
Area treated with predatory mite
The percentage of cultivated area treated with predatory mite against thrips was smaller in 2004 than in 2000. Only for flowering plants did the treated area increase. For vegetables cultivated under glass the percentage was significantly higher - 80 percent or more - than in flower cultivation, where less than 50 percent of the area was treated.
Area treated with predatory mites against thrips in greenhouse culture