Field-cage studies of Beauveria bassiana (Hyphomycetes : Moniliaceae) for the suppression of adult western corn rootworm, Diabrotica virgifera virgifera (Coleoptera : Chrysomelidae)

The efficacy of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vu illemin, was tested as a control agent for adult western corn rootworm, Dia brotica virgifera virgifera LeConte, in walk-in field cages. Suspensions of B. bassiana conidia were applied to corn plants in cages into which labora tory-reared beetles hall been released. Beetles were collected at 3 and 5 d ays post-application and evaluated in the laboratory for mortality. Mortali ty was 10, 29 and 50%, at rate equivalents of 7 x 10(12), 2 x 10(13) (two a pplications), and 5 x 10(13) conidial ha, respectively. There was no signif icant difference in mortality of beetles collected at 3 days compared with 5 clays post-application. Mortality due to B. bassiana was 24% when beetles were released into field cages 24 h post-application (5 x 10(13) conidia/h a) compared with 50% when beetles were present during the application. Beet le mortality declined significantly with increasing time from application i n feeding assays carried out with leaf samples removed from plants at 0, 12 , 24 and 72 h post-application. Mortality of beetles collected from treated plants within cages and maintained in the laboratory was found to overesti mate the population decline by approximate to 10% when compared with beetle estimated from treated plants within field cages.