EVALUATION OF BACILLUS-THURINGIENSIS AND BACILLUS-SPHAERICUS STRAINS FROM CHINESE SOILS TOXIC TO MOSQUITO LARVAE

During our research to isolate and screen microbial agents, eight Baci llus thuringiensis isolates and five Bacillus sphaericus isolates were shown to have high toxicity to mosquito larvae. Comparing the LC(50) values, four B. sphaericus isolates with LC(50) values ranging from 0. 50 to 1.47 ng/ml were about two to six times more toxic than strain 15 93 (LC(50) 3.00 ng/ml) against larvae of Culex quinquefasciatus. Four B. thuringiensis isolates (LC(50) values ranging from 3.80 to 7.54 ng/ ml) and four B. sphaericus isolates with LC(50) of 17.0 to 43.7 ng/ml were more toxic to Aedes aegypti than strain 1897 (LC(50) 8.46 ng/ml) and strain 1593 (LC(50) 67.3 ng/ml). As to Anopheles hyrcanus, the LC( 50) values of three B. sphaericus isolates ranging from 3.63 to 5.73 n g/ml were three to five times smaller than that of strain 1593 (LC(50) 16.1 ng/ml). Two B. sphaericus isolates showed high toxicity against mosquito larvae in the three genera Culex, Aedes, and Anopheles. (C) 1 996 Academic Press, Inc.