Background
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.
Results
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.
Conclusions
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.
: The Kunyushan web-spinning sawfly (Cephalcia kunyushanica) is a major pest in the Japanese red pine (JRP, Pinus densiflora) pure forests in the Kunyushan Mountains of China. In this study, four stand types (ST1–4) were identified in plots of JRP pure forests, based on the pest severity index (PSI; ranging from 0–100). The order of infestation ratio in the four type stands was as follows: ST4 > ST3 > ST2 > ST1. We investigated the correlation of C. kunyushanica occurrence with stand characteristics and soil physicochemical properties in the four stand types. The results showed that all stand characteristics were different among the four stand types. Compared with infested plots, healthy (ST1) plots had a higher soil bulk density, and the differences among the groups were significant. Differences in soil water content, non-capillary porosity, and total porosity were significant among the four ST groups. The average organic matter content, total nitrogen (N), and available N were lower in ST1 plots, whereas total potassium (K) was higher compared with other ST groups. In addition, a redundancy analysis suggested that seven (total N, diameter at breast height (DBH), soil water content, bulk density, available K, zinc ion (Zn2+), and stem density) of 24 environmental variables were significantly correlated with the ordinations of C. kunyushanica occurrence. The results provide theoretical guidance for the ecological control of C. kunyushanica, and are also useful for the management of forests in areas where C. kunyushanica is a major pest and where site and stand conditions are similar.
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