Pesticides and Beneficial Organisms IOBC/wprs Bulletin Vol. 55, 2010 pp. 11-18 11 Field assessment of effects of control strategies against the olive fruit fly (Bactrocera oleae (Rossi)) on predatory arthropods: comparison of different methods of data analysis Susana Pascual 1 , Guillermo Cobos 1 , Pilar Medina 2 , Flor Budia 2 , Elisa Viñuela 2 , Manuel González-Núñez 1 1 Dpto. Protección Vegetal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Carretera de La Coruña Km 7,5, 28040 Madrid, Spain E-mail: mgnunez@inia.es 2 Unidad de Protección de Cultivos. Escuela Técnica Superior de Ingenieros Agrónomos. Universidad Politécnica de Madrid (UPM). Ciudad Universitaria, s/n. 28040 Madrid, Spain Abstract: Numbers of predators captured in a one-year field trial in a Spanish olive grove that received different treatments to control the olive fly (Bactrocera oleae (Rossi)) were analysed with two different statistical analysis methods. The treatments were kaolin (Suround WP), trichlorfon bait spray as a positive control (Trichlorfon + protein hydrolysate (Nulure ® ) and unsprayed control. Two applications of kaolin and one bait spray were done, and fourteen samplings were carried out using a beating method. Two methods of analysis were used: Analysis of variance (ANOVA) and Principle Response Curve analysis (PRC). One-way ANOVA was carried out on total numbers of predators captured at each sampling date and two-way ANOVA was carried out on numbers of specimens of the most abundant taxa, with “treatment” and “sampling date” as factors. Changes in abundance of the different taxa of predators were also investigated using the multivariate method Principle Response Curves (PRC) analysis. Results/conclusions based on one-way ANOVA and PRC analysis were similar, as both showed a significant decrease of the predatory arthropod community in the kaolin treated trees. PRC shows the effect of kaolin on the community of predators in an easier and quicker way, but only allows comparisons between two treatments. Also, PRC gives a global result for the whole season while by using ANOVA it is possible to pinpoint dates in which the effect of treatment is significant. Both PRC and two-way ANOVA identified the coccinellid Scymnus mediterraneus Iablokoff- Khnzorian and the spider family Philodromidae as the taxa the most affected by kaolin. For other, less numerous predatory groups it seems that in general PRC analysis was able to detect effects of the kaolin treatment which were not revealed by two-way ANOVA analysis. Key words: field studies, data analysis, olive, kaolin, predatory arthropods, Principle Response Curve, ANOVA Introduction The olive fruit fly Bactrocera oleae (Rossi) is the most important pest of olive groves. It causes important looses and every year control measures must be applied. The usual tool for controlling the olive fruit fly consists of bait sprays, applying a mixture of an insecticide and an attractant (usually a protein hydrolysate) to attract and kill adults. Kaolin is a fine-grained clay which has been used in crop protection against different pest species in the last few years (Showler, 2002; Marko et al., 2008). Processed kaolin has been shown to be effective in the control of fruit flies, including B. oleae, and other insect pest species on olive trees, such as Prays oleae (Bernard) and Saissetia oleae (Olivier) (De la Roca, 2003; Saour & Makee, 2004; Pascual et al., 2009).