TOXICITY OF MIXTURES OF BACILLUS-THURINGIENSIS WITH ENDOSULFAN AND OTHER INSECTICIDES TO THE COTTON BOIL WORM HELICOVERPA-ARMIGERA

In the laboratory, low concentrations of Bacillus thuringiensis Berlin er (B.t.), as 'Dipel' 2X applied (at about the LC(5)) to cotton leaves enhanced the activity of endosulfan and reduced resistance to endosul fan from approximately seven fold to two fold in neonate larvae of Hel icoverpa armigera (Hubner). Low (LC(5)) concentrations of endosulfan a lso increased the toxicity of B.t. Both endosulfan and B.t. increased the toxicity of the stomach poison cryolite to H. armigera. This incre ased toxicity was not observed where B.t./endosulfan combinations were applied topically to larvae or where B.t. was combined with organopho sphorus or pyrethroid insecticides which are considered primarily to b e contact toxicants. Mixtures of B.t. and endosulfan applied at equito xic concentrations were less toxic than similar concentrations applied alone.