Field evaluation of granular starch formulations of Bacillus thuringiensis against Ostrinia nubilalis (Lepidoptera: Pyralidae)

Bacillus thuringiensis subsp. kurstaki Berliner was encapsulated within cornstarch granules with the feeding stimulant Coax or the UV screen Congo red and tested at two field sites against European corn borer, Ostrinia nubilalis (Hubner), feeding in whorl-stage corn. These tests were done to determine the relative effect of these additives on efficacy of starch-encapsulated B. thuringiensis. At both sites, all treatments with B. thuringiensis significantly reduced tunneling by O. nubilalis. At one site, significant effects of addition of the phagostimulant were observed. When Coax was added at 1 or 10% of starch dry weight with 400 international units (IU) B. thuringiensis per mg dry granule weight, response of O. nubilalis was equivalent to that obtained with granules containing no feeding stimulant and 1,600 IU/mg. Also, granules with Coax and 400 IU/mg gave a response similar to that obtained from the commercial product Dipel 10G formulated at 1,600 IU/mg. At the other site, the effect of phagostimulant was not significant, primarily because O. nubilalis infestation levels were too low for precise discrimination among treatments