On the virulence of two Beauveria bassiana strains against the fall webworm, Hyphantria cunea (Durry) (Lepidoptera: Erebidae), larvae and their biological properties in relation to different abiotic factors

摘要

The genus Beauveria is frequently used as a mycoinsecticides in many countries to control insect pests in agriculture, it is being very effective against the fall webworm, Hyphantria cunea (Durry) (Lepidoptera: Erebidae), which is a pest of trees in forests and orchards. Multiple abiotic factors during fungal growth are well known to influence mycelial growth and several physiological adaptations in the conidia produced. In this study, the pathogenicity of the Beauveria bassiana strains Bb10331 and Bb7725 against H. cunea was evaluated. Peptone potato dextrose agar (PPDA) was used as the medium and colony diameter, conidiation capacity, conidial germination rate were directly affected by relative humidity (RH), illumination, and the ambient pH. The LC50 values of Bb10331 and Bb7725 to H. cunea were 4.72 × 106 and 3.28 × 106 conidia·ml?1, respectively, after 120 h post treatments, while their corresponding LT50 values were 71.13 and 74.54 h at the concentration of 1 × 108 conidia/ml. The Bb7725 had a conidial germination rate than did Bb10331 at the same RH. The two strains grew faster under a dark:light (D:L) photoperiod of 12:12 h, and this particular light condition was also most suitable for their conidia production. The optimum pH for the growth and conidiation of the two strains was approximately 7.0. Both strains are promising for pest control, possessing effective virulence against H. cunea, but this is slightly stronger in Bb7725 than Bb10331. The values of abiotic factors apt to promote the biological properties of each B. bassiana were different.