Dynamics of Tetranychus urticae Koch (Acari: Tetranychidae) in the Presence of the Predatory Mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) in Cotton Under Semi-field Conditions.

Tetranychus urticae Koch is a major pest in cotton crops; in Brazil, the predatory mite Neoseiulus californicus (McGregor) is used for its biological control. Although the standard recommendation for controlling T. urticae is to release around 20,000 individuals per hectare, this is a general guideline and may not be suitable for cotton crops. The present study examined the effect of N. californicus on T. urticae populations in semi-field conditions to identify the predator density needed to reduce pest infestation and the percentage of infested plants. We tested predator-to-prey ratios of 0:50, 3:50, 5:50, and 10:50 on cotton plants maintained in a greenhouse. Tetranychus urticae individuals and the proportion of infested plants were counted daily for the first 5 days, then every 3 days until day 29. All tested densities of N. californicus reduced T. urticae infestation; however, only the release of 5 or 10 predators per 50 T. urticae individuals resulted in infestation levels below the economic threshold level (ETL) recommended for controlling the two-spotted spider mite in cotton crops.