A B. thuringiensis kurstaki was first discovered by H. Dulmage in 1970 and commercialized as a DipelTM due to powerful toxicity to various Lepidoptera. Previously we isolated B. thuringiensis kurstaki on the basis of plasmid DNA profiling and H-antigen serotyping. The aims of this study were to screen larvicidal activities and select the highly active B. thuringiensis isolates against the important polyphagous pests of mandarine oranges and vegetables. The colony forming unit (CFU/ml) of each of culture mixtures was determined to estimate the δ-endotoxin concentration. The bioassay against artificial diet-rearing insects was conducted by surface contamination methods using the Petri dishes specially designed and manufactured by SPL Lifesciences. The insecticidal activities to the natural diet-rearing insect were measured by the application of spore and crystal mixtures to the leaf discs of the chinese cabbage with Potter spray tower. The following insects were used for the larvicidal activities of B. thuringiensis isolates: beet armyworm Spodoptera exigua, diamondback moth Plutella xylostella, giant looper Ascotis selenaria, tobacco cutworm Spodoptera litura, and variegated cutworm Peridroma sucia.

• Sang-Soo Oh(Dept. of Molecular Physiology & Biochemistry, National Institute of Agricultural Biotechnology, RDA)
• Jung Heub Song(Agriculture Environment Division, Jeju Agriculture Research & Extension Services)
• Kyung San Choi(Subtropical Agriculture Environment Division, National Institute of Subtropical Agriculture, RDA)
• Gum Rae Joe(Applied Entomology Division, National Institute of Agriculture Science & Technology, RDA)
• Hyung-Hoan Lee(Department of Biological Sciences, Konkuk University)