Biological control of pollen beetles with the entomopathogenic fungus Beauveria bassiana formulated in oil

Abstract: Pollen beetles (Meligethes spp.) are a major pest in oilseed rape throughout Europe, able to cause substantial yield loss. A laboratory screening of isolates of entomopathogenic fungi revealed high potential of Beauveria bassiana isolates for biological pollen beetle control. To improve the efficacy of entomopathogenic fungi in field applications, we explored synergistic interactions between submerse spores of Beauveria bassiana and other natural compounds that have been shown to reduce pollen beetle abundance in oilseed rape, such as stone dusts or vegetable oils. The combined application of Beauveria bassiana submerse spores and an oil formulation in a spray chamber showed an increase in pollen beetle mortality of up to 40%, relative to single treatments. This was 11% more than expected by mere addition of the effects of single-treatments, suggesting a synergistic interaction between the fungal submerse spores and the oil formulation. The latter seems to foster the fungus’ reproductive phase since twice as many mycosed pollen beetles were recorded in the combined treatment.