Occurrence and diversity of insect-associated fungi in natural soils in China

In the present study, the occurrence and species diversity of insect-associated fungi in soil collected mainly from forest habitats in different regions of China were compared by using the 'Galleria biat method'. Insect-associated fungi were defined to include known insect pathogenic fungi, opportunistic pathogens and secondary colonizers isolated from the Galleria mellonella bait insect exposed to the soil samples in question. Insect-associated fungi were detected in SS.5% of the 425 soil samples. A total of 377 fungi belonging to 46 species and 27 genera were isolated and identified. Among them, 6 species were known insect pathogenic fungi, 21 were opportunistic pathogens and 19 were secondary colonizers. Insect pathogenic fungi were most prevalent and Paecilomyces farinosus, Beauveria bassiana and Metarhizium anisopliae var. anisopliae (Hyphomycetes) were the most common species, comprising 19.6%, 14.1% and 10.6% of the total number of isolates, respectively. opportunistic pathogens also had high occurrences in the soil with the percentage frequency added up to 36.9%. Among the opportunistic fungi, Fusarium oxysporum, F. solani, Geomyces pannorum, Clonostachys rosea f. catenulata and an unidentified Fusarium sp. resulted in the highest G. mellonella mortality in the preliminary pathogenicity test. Using principal component analysis, two components accounted for 76.5% of the total variance were extracted. Component 1 was positively correlated with species richness and species diversity and negatively correlated with the average altitude of the sampling region. Component 2 was negatively correlated with species evenness and positively correlated to the level of insect pathogenic fungi. The two-axis ordination of communities showed clear separation of the fungal community in South Central China, indicating higher occurrence of insect-associated fungi in the soil of subtropical humid region than the other regions. (C) 2008 Elsevier B.V. All rights reserved.