BACILLUS-THURINGIENSIS BERLINER AND BEAUVERIA-BASSIANA (BALSAMO) VUILLIMEN FOR EUROPEAN CORN-BORER CONTROL - PROGRAM FOR IMMEDIATE AND SEASON-LONG SUPPRESSION

Combinations of Bacillus thuringiensis Berliner subspecies kurstaki and Beauveria bassiana (Balsamo) Vuillimen formulated on granules were applied separately and in combination to field corn to suppress larval populations of the European corn borer, Ostrinia nubilalis (Hubner). Research was conducted in 2 separate years. Laboratory-reared O. nubilalis eggs or larvae were placed on the plant during either the whorl stage (V6) or the pollen-shedding stage (R1) to simulate first- and second-generation O. nubilalis oviposition periods, respectively. Efficacy was determined by measuring the length of European corn borer tunnels in the corn stalk at harvest time. In the 1st year, first generation, and second generation (of 2nd year) B. thuringiensis and B. bassiana alone and in combination caused significant reductions in tunneling compared with that in the check populations. There were no significant differences in tunneling between any treatments in the second-generation study of year 1. Bacillus thuringiensis and B. bassiana were independent of each other in their suppression of insects. Tunneling by the naturally occurring second-generation larvae (year 2) was recorded to determine if B. thuringiensis and B. bassiana applied in the V6 stage persisted in the plant. Pith samples were excised from nodal plates 7-10 of the corn stalk to determine the incidence of B. bassiana. There was a significant correlation (r = -0.376) (P less-than-or-equal-to 0.05) between the occurrence of B. bassiana in the corn plant and tunneling by second-generation larvae. These data indicate that B. bassiana placed in the whorl of the corn plant may provide season-long suppression of O. nubilalis.