Effects of biological and chemical insect control agents on fungal community structures in soil microcosms

Abstract

In several European countries the entomopathogenic fungus Beauveria brongniartii is used for specifically controlling the European cockchafer, Melolontha melolontha, a pest in grassland and orchards. This biological control agent (BCA) is applied to soil, where it specifically infects the soil dwelling larvae of M. melolontha. Application of a fungal BCA to soil may potentially affect indigenous soil fungal populations. Therefore, it was the objective of this study to assess and compare such potential effects of the BCA to those of a carbofuran-based chemical control agent (CCA). The experimental system consisted of six soil microcosm treatments with and without larvae of M. melolontha and included BCA- and CCA-treatments. Microcosms were maintained under controlled conditions for 91 days and were sampled three times. Untreated larvae survived until the end of the experiment, whereas all treated larvae died within 28 days. Cultivation-independent quantification of B. brongniartii in soil was based on quantitative real-time PCR analysis of a specific simple-sequence-repeat marker and significantly correlated with cultivation-dependent quantification. Fungal ribosomal internal spacer analysis (RISA) revealed strongest and most significant changes in soil fungal communities for treatments that contained larvae that had died from either control agent. The BCA alone revealed much smaller and transient effects, while effects of the CCA were also small but significantly increased at the end of the experiment. The results revealed that either control strategy induced relatively small effects on soil fungal communities and that molecular genetic tools may be efficiently applied for monitoring and effect assessment of fungal BCAs.