Pest management plan for the two-spotted spider mite, Tetranychus urticae, based on the natural occurrence of the predatory mite Neoseiulus californicus in strawberries

We developed and validated a management plan for Tetranychus urticae in strawberries, based on the natural control exerted by Neoseiulus californicus and on acaricide applications made only when necessary. The plan has two components: a sampling protocol and a decision chart. Systematic presence-absence sampling of active T. urticae and N. californicus was used to predict prey and predator densities relying only on the proportion of T. urticae-infested leaflets, once the occurrence of the predator was detected in at least one of them. The decision chart, which was constructed taking into account the pest and predator densities and the pest's rate of increase, determines the range in the proportion of T. urticae-infested leaflets that will require different actions: to use selective acaricides and re-check at 7 days, to take no action but re-check at 7 days, or to take no action but re-check at 14 days. The management plan was potentially effective and feasible, showing that natural populations of N. californicus can consistently exert strong top-down suppression of T. urticae. Thus, N. californicus is a promising candidate for conservation biological control.