Impact of agricultural management on spider populations in the canopy of olive trees Manuel Ca ´rdenas a, * , Francisca Ruano b , Pedro Garcı ´a c , Felipe Pascual b , Mercedes Campos a a Department of Agroecology and Crop Protection, Estacio ´ n Experimental del Zaidı ´n, C/Profesor Albareda no. 1, 18008-Granada, Spain b Department of Animal Biology and Ecology, University of Granada, 18071-Granada, Spain c Department of Statistics and O.R., University of Granada, Granada, Spain Received 16 September 2005; accepted 9 February 2006 Available online 22 March 2006 Abstract In the province of Granada (southern Spain) spiders were studied in olive-tree canopies, in olive orchards under similar environmental conditions but different management systems: organic, integrated and conventional. Monthly samplings (March to October) was per- formed in the canopy by the beating method. Spider abundance proved significantly higher in the organic than in the conventional orch- ard. An intermediate disturbance level in the integrated regime increased spider diversity, while the conventional management favoured higher dominance of the family Oxyopidae. Four families (Thomisidae, Oxyopidae, Salticidae, and Theridiidae) comprised more than 83% of the specimens captured, of which Thomisidae and Salticidae declined in abundance between organic and conventional manage- ment, whereas the family Oxyopidae was favoured as management disturbance increased. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Araneae; Olive orchard; Managing; Abundance; Diversity; Dominance 1. Introduction Some 96% of the world’s olive orchards (Olea europaea, Linneus) are situated in the Mediterranean area. Spain is the leading producer of olive oil worldwide, with 32.6% of the production, 80% belonging to Andalusia, on a sur- face area that has been increasing in recent years (Civantos, 1997). Different types of orchard management, including differ- ent planting, irrigation, pruning, harvesting, and soil treat- ment (Campos and Civantos, 2000), can have diverse effects, positive or negative, on pest species as well as on useful arthropod groups. Of the three common types of management in Spain (conventional, integrated and organ- ic), the organic and integrated systems had the advantage of higher soil quality and potentially lower negative envi- ronmental impact than in the conventional system (Rega- nold et al., 2001). Many arthropods species take refuge, more or less per- manently, in the olive orchards, including some 100 herbiv- orous insect species and others considered useful or neutral (Arambourg, 1986; Campos and Civantos, 2000; Cirio, 1997; Ruiz and Montiel, 2000; Varela and Gonza ´lez, 1999). Notable among these arthropods are spiders, which as an order represent one of the most abundant and diverse groups of predators in this crop (Morris, 1997; Morris et al., 1999; Pantaleoni et al., 2001; Sacchetti, 1990). These generalist predators can significantly reduce the populations of various insect pests (Marc et al., 1999; Nyffel- er and Sunderland, 2003; Wyss et al., 1995). However, spi- ders tend to be highly sensitive to non-specific pesticides, such as dimethoate or deltametrine (Yardim and Edwards, 1998). In addition, these treatments have an indirect negative www.elsevier.com/locate/ybcon Biological Control 38 (2006) 188–195 1049-9644/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2006.02.004 * Corresponding author. Fax: +34 958129600. E-mail addresses: mcardenas@eez.csic.es (M. Ca ´rdenas), fruano @eez.csic.es (F. Ruano), pgarcia@ugr.es (P. Garcı ´a), fpascual@ugr.es (F. Pascual), mcampos@eez.csic.es (M. Campos).