Evaluation of large-scale releases of western predatory mite for spider mite control in cotton

We evaluated economically feasible release rates of the western predatory mite, Galendromus occidentalis, for spider mite control in organically and conventionally managed commercial cotton fields. An important feature of the experimental design was the evaluation of predatory mite releases at a large spatial scale; the majority of plots were near 2 ha. Predatory mite releases did not enhance the density of the western predatory mite, and populations of western predatory mites remained very low throughout the growing season. However, predatory mite releases did appear to reduce the seasonal abundance of spider mites. Nevertheless, spider mite densities exceeded economic thresholds in many of the release plots, and neither early releases (3–6 nodes per plant) or late releases (>7 nodes per plant) enhanced seed cotton yields. We discuss some potential factors that could have limited the impact of the released predatory mites.