The medium for fermentation has been selected by means of orthogonal designs. The number of cell has reached 10~(11)/ml, and spore forming rate is 70—80%. LC_(50) of mosquito larvicied is lower than 0.125 ppm. Three targets are obviously better than those of previous report. The stable results are proved by studying of fermentation in shaking flask and further in 50L~3-bench fermenter. The production cost of per ton is decreased by 33%.

cryⅢ gene,they were found in 75 6%,67 9%,58 4% and14 5% of the strains respectively,no cryⅠ Ⅴ gene was found,10cry gene combination types were concluded.The Bt isolates which contained cryⅠ genes were further characterized by additional PCR detection with specific primers of the cryⅠAc,cryⅠC and cryⅠE genes.20 Bt isolates which contained cryⅠAc,cryⅠC,cryⅡ and cryⅤ genes were found,among them the strain Bt\|15A3 is high toxic to Heliothis armigera,Spodoptera exigua and Plutella xylostella,and has potential developing and applying value.