Impacts of conventional and organic agriculture on soil-borne entomopathogenic fungi

The entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae sensu lato (s.l.) kill agricultural pests and can diminish pest outbreaks.  Achieving a better understanding of these organisms is an essential step in developing strategies to conserve entomopathogenic fungi in agricultural systems.  We hypothesize that organic farming methods increase the abundance of soil-borne entomopathogenic fungi.    In 2011 and 2012, soil was collected from organic and conventional fields of corn and soybean, and from the field margins.  Entomopathogenic fungi from the soil samples were quantified with larval Galleria mellonella and colony forming units were counted on plates with selective growth medium.  Field history and soil properties were analyzed with multiple regression to determine what factors may affect the abundance of soil-borne fungal entomopathogens.  In 2011, occurrence of Metarhizium anisopliae s.l. and B. bassiana was lowest in conventional fields.  For Metarhizium anisopliae s.l., the average number of colony forming units per gram of dry soil was lowest in conventional fields.  Multiple regression analysis revealed that abundance of Metarhizium anisopliae s.l. was positively associated with applications of organic fertilizer and silt content, and negatively associated with nitrogen content, tillage and herbicide applications.