Pathogenicity of several fungal species on Helicoverpa armigera in different conditions

Virulence of the five fungal species (total 10 strains) to H.armigera larvae was tested by setting up different conidial doses and temperature conditions. The results showed as follows: (1) Virulence of different fungal species and strains was various. Beauveria bassiana and Nomuraea rileyi had obvious controlling efficacy to H.armigera, and the former is prior to the latter. Virulence of the B.b strain 5S03 to H.armigera was the highest, the LT 50 for the 1st and 2nd instar larvae was about from 6.70 to 7.02 days, with adjusted death rates from 86.96 to 91.30 percent and muscardine cadaver rates from 20.00 to 36.67 percent.(2) The difference of virulence of the same strain was extremely obvious for different physiological condition and different instar larvae, the new ecdysial larvae were subject to injecting, the muscardine cadaver rate reached at 85.71 percent. The young instar larvae were more sensitive, and the difference reached at more than 35 percent for adjusted death rates and more than four days for LT 50 compared with the old instar larvae.(3)The most suitable density of 5S03 to control H.armigera was 7.8×10 7 conidia/ml, and temperature was from 20 to 25 ℃.