COMPARATIVE TOXICITIES OF CRYSTAL SEROTYPES OF BACILLUS THURINGIENSIS FOR LARVAE OF PHILOSAMIA CYNTHIA VAR RICINI

Preparations of crystals from 14 strains of Bacillus thuringiensis, representing 6 crystal serotypes, were fed to third-instar larvae of Philosamia cynthia var. ricini. Dosages at 50% mortality with 95% fiducial limits were estimated by probit analysis of mortality rates 24 hr after feeding. The level of toxicity was related to the antigenic composition of the alkali-dissolved crystal and of the active soluble toxin in 11 of the 14 strains. It is concluded that differences in pathogenicity between strains of B. thuringiensis are related to differences in the antigenic composition of the active toxin. © 1969.