Effect of ground-cover management on spider mites and their phytoseiid natural enemies in clementine mandarin orchards (I): Bottom-up regulation mechanisms

Abstract

Tetranychus urticae Koch (Acari: Tetranychidae) is an important pest of citrus that can also feed on most plant species occurring in the ground cover associated with this crop. To determine the effect of managing the ground cover on the biological control of this mite, we have studied the dynamics of both tetranychid and phytoseiid mites in four commercial citrus orchards under three different ground cover management strategies: (1) bare soil, (2) resident wild cover and (3) a sown cover of Festuca arundinacea Schreb. (Poaceae). The results obtained provide evidence that both bottom-up and top-down regulation processes related to the nature of the ground cover affected the tetranychid mite populations in citrus orchards (Panonychus citri (McGregor), Tetranychus evansi Baker & Pritchard and T. urticae). Best results were obtained with the ground cover of F. arundinacea, which did not allow the establishment of T. evansi, and offered a better regulation of both P. citri and T. urticae than either bare soil or the resident wild cover. We hypothesize that the selection of a host race of T. urticae specialized in F. arundinacea when this plant was used as a cover crop could partly explain the results obtained. Further trap cropping effects could also be relevant (bottom-up regulation).