| Abstract: | In the laboratory, low concentrations of Bacillus thuringiensis Berliner (B.t.), as ‘Dipel’ 2X applied (at about the LC5) to cotton leaves enhanced the activity of endosulfan and reduced resistance to endosulfan from approximately seven fold to two fold in neonate larvae of Helicoverpa armigera (Hubner). Low (LC5) concentrations of endosulfan also increased the toxicity of B.t. Both endo-sulfan and B.t. increased the toxicity of the stomach poison cryolite to H. armigera. This increased toxicity was not observed where B.t./endosulfan combinations were applied topically to larvae or where B.t. was combined with organophosphorus or pyrethroid insecticides which are considered primarily to be contact toxicants. Mixtures of B.t. and endosulfan applied at equitoxic concentrations were less toxic than similar concentrations applied alone. |
