ROLE OF THE PREDATORY MITES AMBLYSEIUS-ABERRANS (OUD), TYPHLODROMUS-PYRI SCHEUTEN AND AMBLYSEIUS-ANDERSONI (CHANT) (ACARI, PHYTOSEIIDAE) IN VINEYARDS .2. MINIMUM RELEASES OF A-ABERRANS AND T-PYRI TO CONTROL SPIDER-MITE POPULATIONS (ACARI, TETRANYCHIDAE)

The results of experiments carried out on the releases of phytoseiid mites Amblyseius aberrans (Oud.) and Typhlodromus pyri Scheuten in a vineyard infested by the tetranychid mites Panonychus ulmi (Koch) and Eotetranychus carpini (Oud.) are reported. Increasing densities of predators (10, 25, 40, 50, 100 overwintering females per plant) were released at the beginning of the experiments. Simultaneous releases of the two species were carried out at different ratio to complete previous observations on the competition between the species. The A. aberrans populations controlled the spider mites at low densities independently from the initial release density used. T. pyri seemed more efficient in containing the P. ulmi populations than those of E. carpini. The T. pyri populations declined in the last summer corresponding to high temperatures while the A. aberrans populations seemed not affected by them. In the plots receiving mixed releases of the two species A. aberrans displaced T. pyri within the first year.