Comparative virulence of Beauveria bassiana isolates against clover root weevil (Sitona obsoletus)

Clover root weevil (Sitona obsoletus) (CRW) is of Palearctic origin and in New Zealand has become an invasive pest of white clover. A major survey was undertaken in 2000 to identify and collect the most promising CRW biocontrol agents from a wide range of locations in Europe and the UK. Subsequently several Beauveria bassiana strains obtained from from the cadavers of weevils originally collected live from England, Wales, France, and Romania were isolated in containment at AgResearch, Lincoln. Thereafter bioassays using New Zealand field-collected CRW populations showed that all the European isolates were virulent against the adults, with two being particularly effective. Notably, all of the European B. bassiana isolates exhibited greater virulence against CRW than a New Zealand isolate collected from local CRW populations and a commercial B.bassiana product registered in the USA as BotanigardR. The importance of B.bassiana strain-host association is discussed in relation to the potential effectiveness of entomopathogen-based biological control.