Effect of pollen quality on the efficacy of two different life-style predatory mites against Tetranychus urticae in citrus
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Cover crops can serve as a reservoir of natural enemies by supplying alternative food sources as pollen. However, pollen quality and availability can modulate phytoseiid communities. In clementine trees associated with a cover crop of Festuca arundinacea Schreber, these communities were more diverse than those associated with a multifloral wild cover crop. As a consequence, the former had a better regulation of Tetranychus urticae Koch (Acari: Tetranychidae) populations than the latter. Longer provision of higher quality pollen in the multifloral cover relative to F. arundinacea is suspected to interfere with the biological control of T. urticae by specific phytoseiid predators (Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor)) by enhancing the less efficient generalist pollen feeder Euseius stipulatus (Athias-Henriot) which is a superior intraguild predator. To determine whether pollen quality is behind these results, the effect of the provision of two different pollens (Carpobrotus edulis (L.) L. Bolus and F. arundinacea) on the efficacy of two phytoseiid species (E. stipulatus and N. californicus) to regulate T. urticae populations has been studied under semi-field conditions. Results suggest that pollen provision does not enhance the ability of these phytoseiids to reduce T. urticae populations. However, C. edulis pollen resulted in explosive increases of E. stipulatus numbers that did not occur with F. arundinacea pollen. Therefore, poor quality pollen may prevent pollen feeders from reaching high numbers in the field. This effect could benefit phytoseiid species suffering intraguild predation by E. stipulatus, the predominant phytoseiid species in Spanish citrus orchards and explain field results. (C) 2012 Elsevier Inc. All rights reserved.