Isolation, distribution and toxicity of Bacillus thuringiensis from warehouses in China

Using acetate selection to screen dust samples and cadavers of insect, Baci llus thuringiensis was isolated from 122 of 413 samples obtained from vario us warehouses, processing facilities and animal feed mills. Abundance of B. thuringiensis in the settled dust samples of different origins was differe nt. Among them, B. thuringiensis were most abundant in the settled dust sam ples from warehouses storing rice bran and gunny-bag, in which 46 and 50% o f samples contained B. thuringiensis, respectively. The B. thuringiensis in samples from mountainous region and hilly country were more abundant than that from lowland areas, in which 41 and 20% of samples contained B. thurin giensis, respectively. These B, thuringiensis isolates belonged to serotype s H3, H4, H5, H7, H8, H10, H23 and H27. Among them, serotypes H4 and H5 wer e most abundant and amounted to 36 and 24% of isolates, respectively. The B . thuringiensis from different types of warehouses and regions was differen t in terms of H-serotype. There is rich diversity of toxicity to insects in B. thuringiensis isolates from warehouses; 58 and 71% of the isolates were toxic to larvae of Plodia interpunctella and Spodoptera exigua, respective ly, causing more than 60% mortality. Most isolates were not toxic to Phaedo n brassicae and Culexpipiens fatigans; only one isolate was highly toxic, c ausing more than 90% mortality to both species. (C) 2000 Elsevier Science L td. All rights reserved.