Biological control by predatory mites (Phytoseiulus persimilis Athias-Henriot) of red spider mite (Tetranychus urticae Koch) infesting strawberries grown in walk-in' plastic tunnels

SUMMARY During 1 978 and 1979, the control of red spider mite on strawberries by the predacious mite Phytoseiulus persimilis was studied at two sites in Hampshire where crops were grown in ‘walk-in’ plastic tunnels. An introduction of at least two predators per plant in March was required to control red spider mite in one experiment. In the second experiment, introductions of small numbers of predators (fewer than two per plant) in August controlled mites on newly planted runners before diapause. Similar numbers of predators introduced in the following March, 10 days after red spider mite eggs were seen, controlled mite infestations throughout the growing season. Controlling mites in the autumn before diapause was considered important.