| Beauveria bassiana (Balsamo) Vuillemin is one of the entomopathogenic fungi which applied the most widely presently at home and abroad, to pest control effectively. It could infect more than 700 Species insects of 149 Families in 15 Orders. Different strains of beauveria bassiana have differnet virulences aganist different insects. In this paper, the strains of HFW-05, Lu-08, Dj-04 and TE-07 as the different types of specie, whose biological characteristics and the virulence against the Plutella xylostella and the Helicoverpa armigera would be studied. The infection processes of the four strains on cuticle of the Plutella xylostella and the Helicoverpa armigera were observed, using scanning electron microscope. This study shows that three enzymes play a improtant role in the infection process , and the chitinase gene of four strains of Beauveria bassiana were cloned.This study shows that four strains of Beauveria bassiana are different types under the same specie by the ITS sequences and the analysis of esterase isoenzymograms. The virulence against the 2rd of the Plutella xylostella and the Helicoverpa armigera were measured. The results indicated that the strain of HFW-05 was high virulent to the Plutella xylostella and the correct mortality after 6 days could be 87.14%, other three strains could be lower than 40%. The correct mortality of the four strains to the Helicoverpa armigera could be lower than 15%.The infection processes of the conidia on cuticle were observed using scanning electron microscope. The results showed that most of conidia were deposited on cavities, setae, folded regions and acanthoid surface topography. The penetration occurred directly or the germ tubes produced. The germ tubes of strain HFW-05 which grow on the integument or bended to integument of the Plutella xylostella were shorter than that of other strains before penetration occurred, which depositeed after 16 h. Conidia germinated in the surface of Helicoverpa armigera for the four strains, but the germ tubes grew extensively and penetrations were not observed. Blastospore were observed within 36 h postinoculation for the four strains.The virulence of the low-virulent strains against the insects processed with lipase, proteinase K, chitinase and four compound enzymes respectively have certain degree rise, and the treatment of chitinase and compound enzymes which contain chitinase to strains were improved markedly. There were significant differences of the relative mortality to the Plutella xylostella after 6 days between treatments of diffenent enzymes(F=17.695, P<0.05). After chitinase treatment, the relative mortality of the Lu-08 strain which increased most obviously was 2.9 times of the CK. After lipase treatment, the relative mortality of the Dj-04 strain which increased most unobviously was 1.15 times of the CK. There were significant differences of the relative mortality to the Helicoverpa armigera after 6 days between treatments of diffenent enzymes(F=17.695, P<0.05). The relative mortality of the HFW-05, TE-07, Lu-08, Dj-04 strains to the Helicoverpa armigera treated by chitinase after 6 days which increased most obviously were 4.52, 5.55, 37.33, 17.12 times of the CK. It reflects chitinase of strains have bigger influence to the virulence than the lipase and proteinase K during the process of infection.The chitinase genes were firstly cloned from the strains. Sequence analysis revealed the same DNA sequence with a length of 1047 bp and encoded an open reading frame consisting of 348 amino acids of 36.795 kD peptide. The analysis shows that the gene sequence exhibited 98% identity to that of Besuveria bassiana NCIM1216 chitinase(EU828354) and Besuveria bassiana Bb0062(AY145400). The deduced amino acid sequence exhibited 99% identity to that of Besuveria bassiana Bb0062 chitinase(AAN41259) repectively. This could be related to the diversity of chitinase genes from Beauveria bassiana and the coordination function in the process of infection.
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