STRAIN OF BACILLUS-THURINGIENSIS SEROVAR KURSTAKI WITH INCREASED UV RESISTANCE AND LEPIDOPTERAN LARVICIDAL ACTIVITY

A highly UV-resistant strain, designated UVR-M, of Bacillus thuringien sis serovar kurstaki was produced by selection using repeated exposure to UV irradiation. The difference in the UV resistance levels between the UVR-M strain and the HD-I (serovar kurstaki) strain was more than 100 times. This resistance was observed in both spores and vegetative cells. When compared to the HD-I strain, the WR-M strain was 1.5 time s more prolific in production of spore/crystal complexes, and 1.75 tim es more active against silkworm (Bombyx mori) larvae. Larvicidal activ ity tests with six selected lepidopterous pests showed no significant difference between the two strains in activity against Phutella xylost ella, Spodoptera litura, Spodoptera exigua, and Homona magnanima. Howe ver, the UVR-M strain was five times and 20 times more active against Spodoptera depravata and Adoxophyes sp., respectively, compared to the HD-1 strain. The field persistence of the activity and the spore viab ility of the UVR-M strain was far greater than that of the HD-1 strain .