ROLE OF AMBLYSEIUS-ABERRANS (OUD), TYPHLODROMUS-PYRI SCHEUTEN AND AMBLYSEIUS-ANDERSONI (CHANT) (ACARI, PHYTOSEIIDAE) IN VINEYARDS .3. INFLUENCE OF VARIETY CHARACTERISTICS ON THE SUCCESS OF A-ABERRANS AND T-PYRI RELEASES

The influence of leaf features on the colonization of the phytoseiid mites Amblyseius aberrans (Oud.) and Typhlodromus pyri Scheuten was studied by releasing the predators in 5 vineyards, each having 2 different grape varieties characterized by glabrous or hairy leaf undersurfaces. A. aberrans and T. pyri population densities were more abundant on varieties characterized by hairy leaf undersurfaces (Raboso, Verduzzo, Trebbiano). Phytoseiid dynamics showed remarkable differences under conditions of prey scarcity, suggesting that the reference for certain varieties was largely independent of prey availability. This preference appears to be linked to a favourable microclimate, improved protection from being washed away or from macropredators, large availability of oviposition sites and shelters and an increased capacity for retaining wind pollen. The phytoseiids' preference for a variety is an important factor which influences their persistence on arboreal plants under conditions of prey scarcity and probably determines a more efficient response to spider mite increases. A better knowledge of these relationships will constitute an improvement in using phytoseiid mites in biological control programmes.