Potential control of Swiss wireworms with entomopathogenic fungi

Abstract: The main wireworm species reducing the quality of potato tubers in northernSwitzerland are Agriotes obscurus, A. lineatus and A. sputator. In this study, the effect of theSwiss Metarhizium anisopliae strain ART-2825 and of Naturalis® (Beauveria bassiana) on thesewireworm species was evaluated in the laboratory, in the greenhouse and in the field. In alaboratory bioassay, larvae of the three Agriotes species treated with Naturalis® product andNaturalis® spores did not exceed the infection rate of the control treatment. Similarly, nosignificant effect of Naturalis® was observed in a potato field, with 79% percent damaged tubersin the control and 82% in the Naturalis® treatment. In contrast, M. anisopliae strain ART-2825demonstrated a high virulence towards A. obscurus in two laboratory bioassays. Nine weeks postinoculation,80% and 97% infected A. obscurus larvae were observed in bioassay 1 and bioassay2, respectively. However, the virulence of strain ART-2825 against A. lineatus and A. sputatorwas considerably lower with maximum infection rates of 50%. Application of strain ART-2825onto sterile and non-sterile soil in pots in the greenhouse resulted in a significant reduction ofsurviving A. obscurus larvae. The corrected efficacy according to Abbott of strain ART-2825 was61% in sterile and 50% in non-sterile soil. The results suggest that Naturalis® is not suitable tocontrol wireworms in potato fields in northern Switzerland. However, M. anisopliae strain ART-2825 may be investigated further as a means to control wireworms in Swiss IPM programmes.