Modifying soil to enhance biological control of belowground dwelling insects in citrus groves under organic agriculture in Florida Raquel Campos-Herrera a,b,⇑ , Fahiem E. El-Borai a,c , Larry W. Duncan a a Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd, Lake Alfred, 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 highlights  Manure and biocontrol fungi approved for organic citriculture were evaluated in the field.  Impact on the citrus soil food web (weevil, nematodes, fungi and bacteria) were evaluated.  Amendments did not produce major changes in the entomopathogenic nematode community.  Both amendments marginally reduced the number of weevils emerging from soil.  The two amendments might contribute to protection of citrus under organic production. graphical abstract article info Article history: Received 5 November 2014 Accepted 16 February 2015 Available online 21 February 2015 Keywords: Organic production Entomopathogenic nematodes Mulch Fungal biological control Soil food webs abstract An emerging organic citrus industry in Florida could benefit greatly from effective, non-conventional meth- ods to mitigate losses from pests and diseases. We studied part of a soil food web in an organic orchard to learn ways to conserve and enhance biological control of insect pests by native entomopathogenic nema- todes (EPNs). We evaluated two OMRI (Organic Materials Review Institute) approved cultural practices: (i) a mulch of commercially pelleted chicken manure, (ii) a commercial formulation of Purpureocillium lilaci- nus, and (iii) an un-amended control. Several soil nutrients (i.e. nitrogen, phosphate, and potassium) were affected by the amendments, but initial equilibrium values (T0) were restored by the last sampling time (T12). The plant parasitic nematode Tylenchulus semipenetrans increased in both treatments compared to the untreated control at T3 (P < 0.05). The oomycete Phytophthora nicotianae increased in the P. lilacinus plots at T1, marginally at T12, but decreased at T6 and T9. Steinernema diaprepesi, Heterorhabditis indica and Heterorhabditis zealandica were the only EPNs regularly detected in the orchard. Mulch increased num- bers of H. zealandica at T6 and T9 (P < 0.05) and free living nematodes at T12 (P < 0.01). The nematophagous fungus (NF) P. lilacinus persisted in plots where it was augmented (P < 0.05), reaching a maximum level at T3 that was 17.5-fold greater than that in controls. Numbers of Paenibacillus sp. were directly related to both those of S. diaprepesi and Acrobeloides-group nematodes (P < 0.01), but inversely to the FLN counts (P < 0.05). The application of these two amendments did not produce strong changes in the EPN community but decreased the emergence from soil of adult Diaprepes abbreviatus, a root weevil pest. Thus, both amend- ments might contribute to citrus pest management under organic production. Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.biocontrol.2015.02.002 1049-9644/Ó 2015 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: University of Neuchâtel, Emile-Argand, 11, CH-2000 Neuchâtel, Switzerland. E-mail addresses: raquel.campos@ica.csic.es, r.camposherrera@ufl.edu, raquel. campos@unine.ch (R. Campos-Herrera). Biological Control 84 (2015) 53–63 Contents lists available at ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon