CHANGES IN THE POPULATIONS OF TETRANYCHID MITES AND THEIR PREDATORS

In the first year of the experiment (1992) three species of tetranychid mites, fruit tree red spider mite (Panonychus ulmi Koch), two-spotted spider mite (Tetranychus urticae Koch), hawthorn red spider mite (T. viennensis Zacher) occurred in the experimental orchard. Predacious mite did not occur previously in this orchard. Among them Zetzellia mali (Ewing), a stigmaeid mite, appeared at first in the IPM plot in June and in a few number at the end of the summer in the conventional plot. The specimens of the minute black ladybird (Stethorus punctillum Weise) and flower bug (Orius niger Wolff) appeared in the experimental orchards. Their population level was higher in the conventional plot, connected with the high population density of the fruit tree red spider mite.

In the second year of the experiment (1993) the population density of the Zetzellia mali appeared both in the conventional and IPM plots. It has become an effective regulating factor of the phytophagous mites. The specimens of the phytoseiid mites appeared in both plots, but in the conventional plot they were present only occasionally, in low numbers.

In the third year of the experiments (1994) the regular use of the selective insecticides made it possible to develop such a community which involved phytophagous and zoophagous population and as well as the alternative food sources of the zoophagous species. In these communities the density of the tetranychid mites can not extremely fluctuate, their population level does not reach the economic threshold.

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