Toxicity of Bacillus thuringiensis strains and commercial formulations to the diamondback moth, Plutella xylostella (L,)

Toxicity of spore-crystal complexes and commercial formulations of Bacillus thuringiensis (BE) was evaluated against second instar larvae of the diamo ndback moth, Plutella xylostella (L.) by leaf dip bioassay. Forty-eight hou rs median lethal concentrations (LC50) showed significantly high toxicity o f Bt strains producing a mixture of Cry1Ab with other Cry1 and Cry2 toxins (Bt kurstaki HD-1 and Bi aizawai HD-137). Bt strain-producing Cry1Aa was no t toxic to larvae of the diamondback moth whereas strains producing single or two Cry toxins showed an intermediate toxicity. Of the commercial formul ations of Bt kurstaki, Biobit (R) was 6.7, 7.8 and 13.5 fold more toxic tha n Dipel (R), Halt (R) and HIL (R) products. (C) 2001 Elsevier Science Ltd. All rights reserved.