Aptness of insecticides (Bacillus thuringiensis and carbofuran) with endophytic Beauveria bassiana, in suppressing larval populations of the European corn borer

Research was conducted in 1989 and 1990 to determine if Beauveria bassiana in combination with Bacillus thuringiensis or carbofuran is an effective tactic for season-long management of the European corn borer, Ostrinia nubilalis. A granular formulation of Beauveria bassiana was applied to corn at whorl stage (V6) and/or at pollen-shed stage (R1) corn. Bacillus thuringiensis or carbofuran was then applied to the same plants. Beauveria bassiana reduced larval populations of O. nubilalis when the fungus was applied to corn during both the whorl stage and the pollen-shed stage. When either Bacillus thuringiensis or carbofuran was added to plants treated with Beauveria bassiana, there was increased mortality of O. nubilalis. Although Beauveria bassiana alone reduced O. nubilalis tunneling, mostly damage was further reduced when Bacillus thuringiensis or carbofuran was applied to whorl-stage corn. When applied to pollen-shedding corn, Beauveria bassiana reduced tunneling but had no significant effect on yield, unless Bacillus thuringiensis was added. Although Beauveria bassiana, Bacillus thuringiensis, and carbofuran reduced tunneling by first generation O. nubilalis, increased yields did not always result. Tunneling by second-generation O. nubilalis was significantly reduced by Beauveria bassiana in both years of all experiments. Even so, yields were variable in all experiments which indicated that a number of abiotic and biotic factors, aside from insects, affected yields. This study is the first to document compatibility of Beauveria bassiana with a chemical insecticide. Yield data indicate that endophytic Beauveria bassiana is not a plant pathogen.