Local isolates of Beauveria bassiana for control of the coffee berry borer Hypothenemus hampei in Puerto Rico : Virulence, efficacy and persistence

The coffee berry borer Hypothenemus hampei (CBB) is a major pest of coffee, and the entomopathogenic fungus Beauveria bassiana (Bb) is used worldwide for its biological control. Commercial formulations of Bb are sprayed on coffee, but local isolates of Bb may also provide some level of natural control. We compared selected local Bb isolates from CBB-infested coffee fruits in Puerto Rico against the commercial strain, GHA, derived from Mycotrol (R). Isolates were tested for their virulence toward CBB in vitro. Two local isolates and the commercial isolate were sprayed on coffee plants in the field, and percent CBB infected, percent fruits with CBB damage, and number of CBB per fruit were surveyed over eight weeks in three consecutive years. Genotypes of Bb isolates in the field were discriminated with microsatellites to determine if isolates persisted after application. Several local isolates and mixtures of isolates were as virulent in vitro as the commercial isolate. In the field, all isolates significantly reduced CBB damage; one local isolate was more successful than the others. Genetic structure of local Bb populations varied from field to field and from year to year. Local isolates persisted; the commercial isolate did not, except in one plot. The commercial isolate may not be adapted to the warm, humid environment of coffee farms. Local isolates and perhaps combinations of isolates can provide more effective control, although current regulations preclude their use.