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Predatory Mite Field Study (IOBC 2000)

Applications of plant protection products should not unacceptably affect non target arthropod populations like predatory mites. Thyphlodromus pyri is a common and important leaf dwelling mite and one of the most important predators of spider mites in vineyards and orchards. A field study on predatory mite populations under the real conditions of agricultural practice (GAP) is indicated if laboratory studies show considerably high effects on mortality and reproduction of T. pyri. It allows determining short and long term effects on predatory mite populations like reduction, persistence and recovery potential.

Study Design

according to Blümel et al. 2000

Test organisms

Predatory mites (Acari, Phytoseiidae), e.g. Typhlodromus pyri Scheuten, living in natural populations, all mobile predatory mite stages are assessed.

Design of the Test field

Genuine vineyard and orchard unities under real conditions of agricultural practice are used as test sites. Beside the water treated control and the test item treatment a toxic reference item is applied to proof the sensitivity of the test system. Each treatment group comprises 5 replicates (15 grape-vines per plot or 8 slender spindle bush trees).

Application of the Test Substances

The application is done with a calibrated back pack sprayer. Time and frequency of the applications follow the intended use of the product. A calibrated volumetric flow instrument gives the exact amount of the actual application.

Exposure Route

Direct spraying, contact to residues, uptake of contaminated food

Mite sampling

Leaves (or buds) are removed randomly from each plot, placed in a labelled bucket and processed in the laboratory. Further procession follows the leaching-method (Boller 1984): Each bucket is filled with tap water adding a small amount of detergence to lower the surface tension of the added water; all leaf of one plot are individually washed with tap water; the washing water of the respective container is poured through a system of several sieves. The retained mites are counted under a binocular. Two subsamples at the beginning and end of the study are identified to species level to determine the species composition of the predatory mite population.

Course of the study

A pre-sampling is done within five days before the first test item application to ensure sufficient abundance and homogeneity of the mite populations. If there are several application dates interim sampling has to be performed. Two post-application sampling are carried out one and four weeks after the last application. The mite samplings are continued in 4 week intervals as long as the reduction of the test item relative to the control is higher than 50%.

Duration: 2 to 12 months depending on recovery of mite population

Endpoints

The development of mite population densities is monitored over the complete experimental period until recovery of the test item treatment is observed.  Recovery is achieved when the reduction of the predatory mite density in the test item treatement relative to control is below 50%.

Guidelines and Literature

  • Blümel et al., 2000: Guidance document to detect side effects of plant protection products on predatory mites (Acari: Phytoseiidae) under field conditions: vineyards and orchards. In: Candolfi et al. (eds.) 2000: Guidelines to evaluate side-effects of plant protection products to non-target arthropods. IOBC/WPRS, Gent, pp 121-143.
  • Boller E. 1984: Eine einfache Ausschwemm-Methode zur schnellen Erfassung von Raubmilben, Thrips und anderen Kleinarthropoden im Weinbau. Schweiz. Zeitschrift für Obst- und Weinbau 120: 16 -17.