Development of biological methods for the control of Tetranychus urticae on tomatoes using Phytoseiulus persimilis

Abstract

SUMMARYThe biological control of red spider mite using the predatory mite Phytoseiulus persimilis was investigated in 1971, 1972 and 1974. Experiments in small glasshouse compartments showed that the predator should be introduced when the leaf damage index is < 0–3.Uniform and/or patch introductions of P. persimilis at different rates were made into naturally occurring red spider mite infestations on commercial nurseries. In eleven of the seventeen experiments good control was achieved. Introduction of the predator soon after damage appeared on the crop was essential. Poor control was obtained when the predator failed to establish itself, where very large numbers of diapausing mites emerged and built up rapidly or where the predator, introduced into patches, failed to colonize infested plants elsewhere in the crop.When spider mites and predators were introduced on to one‐fifth or one‐tenth of the plants in a propagating house, a satisfactory interaction was maintained for 4–6 wk after planting out. The predators then died unless red spider mites emerged from diapause or were introduced.Petroleum oil sprays were sometimes used successfully in the presence of the predator to reduce high red spider mite infestations and re‐establish the biological equilibrium.