Comparative toxicity of pesticides in three phytoseiid mites with different life-style occurring in citrus: Euseius stipulatus, Neoseiulus californicus and Phytoseiulus persimilis

Conservation and augmentative biological control strategies have been developed to take full advantage of the natural enemies that occur in Spanish citrus orchards. Among them, the predatory mites Euseius stipulatus, Neoseiulus californicus and Phytoseiulus persimilis play an important role in the biological control of tetranychid mites. However, these predatory mites are often affected by pesticides and information about the side-effects of these products against these beneficial arthropods is essential to guarantee their efficacy. The side-effects of some pesticides remain unknown and the primary aim of this study was to fill this gap. We have further used this information and that collected from other sources to compare the response of these three mite species to pesticides. Based on this information, E. stipulatus has the most tolerant species, followed by N. californicus and P. persimilis. Therefore, using E. stipulatus as an indicator species in citrus may have led to the paradox of selecting presumed selective pesticides resulting in excessive impact on N. californicus and, especially on P. persimilis. Because these two latter species are considered key for the biological control of T. urticae in citrus, especially clementines, in Spain, we propose to use P. persimilis as the relevant indicator of such effects on predacious mites occurring in citrus instead of E. stipulatus. This change could have a dramatic impact on the satisfactory control of tetranychid mites in citrus in the near future

POLLEN QUALITY AFFECTS BIOLOGICAL CONTROL OF TETRANYCHUS URTICAE IN CLEMENTINE MANDARINES

Tetranychus urticae Koch (Acari: Tetranychidae) populations in citrus can be regulated through the management of the cover crop. A mono-specific cover of the grass Festuca arundinacea Schreber (Poaceae) enhanced the diversity and abundance of Phytoseiidae mites compared with a multifloral cover. This increase resulted in a better control of T. urticae. Pollen availability and quality could be behind this result. Whereas multifloral cover offers a long-term source of a wide variety of pollen, F. arundinacea offers one single type of pollen in spring only. As a consequence, the generalist pollen feeder Euseius stipulatus (Athias-Henriot), which is a superior intra-guild predator, is highly favored in multifloral covers. Therefore, poor quality pollen may prevent pollen feeders from reaching high numbers and indirectly benefit T. urticae control by specialist phytoseiids

Effect of pollen quality on the efficacy of two different life-style predatory mites against Tetranychus urticae in citrus

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

Acta Horticulturae

Tetranychus urticae Koch (Acari: Tetranychidae) populations in citrus can be regulated through the management of the cover crop. A mono-specific cover of the grass Festuca arundinacea Schreber (Poaceae) enhanced the diversity and abundance of Phytoseiidae mites compared with a multifloral cover. This increase resulted in a better control of T. urticae. Pollen availability and quality could be behind this result. Whereas multifloral cover offers a long-term source of a wide variety of pollen, F. arundinacea offers one single type of pollen in spring only. As a consequence, the generalist pollen feeder Euseius stipulatus (Athias-Henriot), which is a superior intra-guild predator, is highly favored in multifloral covers. Therefore, poor quality pollen may prevent pollen feeders from reaching high numbers and indirectly benefit T. urticae control by specialist phytoseiids

Papel del polen en el control biológico de Tetranychus urticae en clementinos

La gestión de las cubiertas vegetales constituye una estrategia de control bio-lógico por conservación a considerar en la regulación de las poblaciones de la araña roja, Tetranychus urticae, en cítricos. En este trabajo se explica como la elección adecuada de la especie vegetal que conformará la cubierta puede ser importante, entre otros factores, por el tipo de alimento (polen) que ofrece a los enemigos naturales de los ácaros tetraníquidos, los ácaros fitoseidos. Un polen de reducida calidad puede impedir que las poblaciones del ácaro fitoseido generalis-ta y palinófago Euseius stipulatus se incrementen explosivamente. Esta reducción en abundancia relativa de este fitoseido puede indirectamente beneficiar a las poblaciones de otros ácaros más eficientes en el control de la araña roja que se encuentran sometidos a su presión, y que no son tan dependientes de la calidad del polen. Este resultado aporta una posible explicación al control más satisfacto-rio de T urticae en clementinos asociados a una cubierta con Festuca arundina-cea, gramínea que ofrece un polen de reducida calidad para Neoseiulus californi-cus y E. stipulatus, los dos fitoseidos estudiados