The effects of cropping systems on entomopathogenic fungi

Naturally-occurring, entomopathogenic fungi provide a valued service of killing agricultural pests and subduing pest outbreaks. Species such as Beauveria bassiana and Metarhizium anisopliae have been studied in great depth and have proven to kill pest insects.  We hypothesize that organic farming methods better suit populations of soil-borne entomopathogenic fungi and that conventional farming methods, coupled with the use of chemicals, could have a directly negative impact on these beneficial fungi.  Better understanding of these organisms is an essential step in developing more robust integrated pest management.  In the summer of 2011, soil from organic and conventional fields (producing corn and soybean) as well as soil from the field margins were sampled and screened for entomopathogens. Fungi were quantified by measuring mortality of Galleria mellonella exposed to collected soil, and by counting colony forming units on selective plate media through serial dilutions. Field history and soil properties were analyzed with multiple regression to determine which agricultural practices and soil properties may affect these fungi.  Galleria mellonella mortality and the abundance of Metarhizium spp. were significantly lower in conventional fields compared to organic fields and their respective margins, and several factors affected the abundance of Metarhizium spp.