MANAGEMENT OF THE SPIDER-MITE POPULATION IN A VINYLHOUSE VINERY BY RELEASING PHYTOSEIULUS-PERSIMILIS ATHIAS-HENRIOT ONTO THE GROUND COVER

It has been observed that Phytoseiulus persimilis, a predatory phytose iid mite, is unlikely to settle on tall host plants, such as woody pla nts. In 1995, an experiment was performed in a vinylhouse vinery (1,00 0 m(2)) in an attempt to manage the spider-mite population of Tetranyc hus kanzawai on grape leaves throughout the growing season, by releasi ng P. persimilis. onto the grass ground cover in the spring. Two relea ses of P. persimilis (a total of 8,000 females) late in May and early in June drove the spider-mite population on the ground cover almost to extinction early in July. Throughout July, the spider-mite density wa s held at 10% of that in the control vinery where no predators had bee n released. Early in August, spider mites reoccurred in the vinery, be cause P. persimilis had died out due to lack of prey. However, since t he population density of spider mites was very low (<1.73 females/leaf ), no chemical control was required throughout the growing season. A s urvey in the following March confirmed that no P. persimilis had survi ved the winter in or around the vinery.