Geospatial patterns of soil properties and the biological control potential of entomopathogenic nematodes in Florida citrus groves Raquel Campos-Herrera a, b, * , Ekta Pathak a , Fahiem E. El-Borai a, c , Robin J. Stuart d , Carmen Gutiérrez b , Jose Antonio Rodríguez-Martín e , James H. Graham a , Larry W. Duncan a a Citrus Research and Education Center (CREC), University of Florida (UF), 700 Experiment Station Road, FL 33850, USA b Instituto de Ciencias Agrarias, CSIC, Serrano 115 Dpdo, Madrid 28006, Spain c Plant Protection Department, Faculty of Agriculture, Zagazig University, Egypt d DPI, Florida Department of Agriculture and Consumer Services, Dundee, FL 33838, USA e Departamento de Medioambiente, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria INIA, Crta. de la Coruña, km 7.5, 28040 Madrid, Spain article info Article history: Received 3 May 2013 Received in revised form 12 July 2013 Accepted 13 July 2013 Available online 1 August 2013 Keywords: Entomopathogenic nematodes Multivariate analysis Quantitative real-time PCR Ecology Food web Geospatial patterns abstract Entomopathogenic nematodes (EPNs) are widely distributed in natural and managed ecosystems worldwide. Due to the cryptic nature of soil food webs, EPN ecology and their role in modulating insect population dynamics remain largely a matter of speculation. A weevil pest of citrus, Diaprepes abbre- viatus, is less abundant in orchards on the central ridge (hilly topography, deep, coarse sand soils) than in the flatwoods (flat topography, fine sand soils with a high water table). We speculate that native EPNs are a key factor regulating these weevils and thus hypothesized that EPNs are most abundant and/or species diverse in central ridge orchards. In this study, we measured and analyzed the natural distributions of EPNs in these two regions concomitantly with those of selected abiotic and biotic soil components. Our objective was to identify physical properties that can potentially be manipulated to conserve native EPNs that serve to control D. abbreviatus. We used species-specific qPCR probes for i) 13 EPN species, ii) two species of Paenibacillus that are ectoparasitically associated with EPNs, iii) free-living bacteriophagous nematodes (Acrobeloides-group) that might compete with EPNs, and iv) oomycete pathogens of citrus roots, Phytophthora nicotianae and Phytophthora palmivora. Citrus orchards were surveyed in eco-regions categorized as central ridge (23 localities) and flatwoods (30 localities). EPNs and Acrobeloides-group were detected in all sites and the abundances of the two guilds were positively related. Heterorhabditids comprising two species occurred in more localities at higher numbers than did five steinernematid species. Heterorhabditis indica dominated flatwoods communities, whereas communities with abundant Steinernema diaprepesi, Heterorhabditis zealandica and H. indica occurred on the central ridge. Spatial patterns of S. diaprepesi were more aggregated than those of H. indica and other dominant species. The central ridge supported greater EPN evenness, diversity and species richness. For the first time, quan- titative natural positive associations between EPNs and two species of Paenibacillus bacteria were assessed. The oomycete pathogen P. palmivora was only detected in the flatwoods, whereas P. nicotianae was widespread and equally abundant in both regions. Four variables that affect soil water potential (groundwater depth, available water capacity, clay and organic matter content) significantly contributed to explain the variability in a redundancy analysis of the selected soil communities. Management of soil water potential may aid in establishing and conserving diverse EPN communities that provide more effective control of Diaprepes root weevils. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Florida citrus orchards are planted in eco-regions known broadly as central ridge and flatwoods based on soil texture and water drainage. The central ridge is comprised of deep, coarse * Corresponding author. Citrus Research and Education Center (CREC), University of Florida (UF), 700 Experiment Station Road, FL 33850, USA. Tel.: þ1 863 956 111, þ1 863 9564631. E-mail addresses: r.camposherrera@ufl.edu, raquel.campos@ica.csic.es (R. Campos-Herrera). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.soilbio.2013.07.011 Soil Biology & Biochemistry 66 (2013) 163e174