Long-term field persistence of Beauveria brongniartii strains applied as biocontrol agents against European cockchafer larvae in Switzerland

In field tests between 1985 and 1992, various sites which were infested with Melolontha melolontha were treated with the biocontrol fungus Beauveria brongniartii. The fungus was applied either as blastospores or as commercially available fungus colonized barley kernels (FCBK). In 1998/1999, soil samples were collected from the test sites and B. brongniartii isolates recovered and maintained in a culture collection. Isolates from this collection were subjected to genetic analyses by use of specific microsatellite markers. The applied B. brongniartii strains were detected at all test sites up to 14 years after their application. At some sites, the B. brongniartii populations consisted of the applied strains exclusively, whereas at other sites, indigenous populations or isolates that may have arisen from mutations or interactions among the applied strains and indigenous isolates were present in addition to the applied strains. The results suggested that applied B. brongniartii strains and indigenous B. brongniartii populations could coexist in the same habitat. Demonstration of long-term persistence of the applied B. brongniartii strains in the fields supported the success of this approach for the biological control of M. melolontha.