Effects of the Entomopathogenic Fungus <i>Metarhizium anisopliae</i> on the Mortality and Immune Response of <i>Locusta migratoria</i>

• Main Authors: Wuji Jiang, Yifan Peng, Jiayi Ye, Yiyi Wen, Gexin Liu, Jiaqin Xie
• Format: Article
• Language: English
• Published: MDPI AG 2019-12-01
• Series: Insects
• Subjects: <i>metarhizium anisopliae</i>; mortality; <i>locusta migratoria</i>; immune response; pest control
• Online Access: https://www.mdpi.com/2075-4450/11/1/36

Entomopathogenic fungi are the key regulators of insect populations and some of them are important biological agents used in integrated pest management strategies. Compared with their ability to become resistant to insecticides, insect pests do not easily become resistant to the infection by entomopathogenic fungi. In this study, we evaluated the mortality and immune response of the serious crop pest <i>Locusta migratoria manilensis</i> after exposure to a new entomopathogenic fungus strain, <i>Metarhizium anisopliae</i> CQMa421. <i>M. anisopliae</i> CQMa421 could effectively infect and kill the <i>L. migratoria</i> adults and nymphs. The locust LT₅₀ under 1 &#215; 10⁸ conidia/mL concentration of <i>M. anisopliae</i> was much lower than that under conidial concentration 1 &#215; 10⁵ conidia/mL (i.e., 6.0 vs. 11.2 and 5.0 vs. 13.8 for adults and nymphs, respectively). The LC₅₀ (log₁₀) of <i>M. anisopliae</i> against locust adults and nymphs after 10 days was 5.2 and 5.6, respectively. Although the number of hemocytes in <i>L. migratoria</i> after exposure to <i>M. anisopliae</i> did not differ with that in the controls, the enzymatic activity of superoxide dismutase (SOD) and prophenoloxidase (ProPO) did differ between the two treatments. The activities of both SOD and ProPO under the <i>M. anisopliae</i> treatment were lower than that in the controls, except for the ProPO activity at 72 h and the SOD activity at 96 h. Further, the expression of the <i>L. migratoria</i> immune-related genes defensin, spaetzle, and attacin differed after exposure to <i>M. anisopliae</i> for 24 h to 96 h. Taken together, this study indicated that infection with <i>M. anisopliae</i> CQMa421 could cause the death of <i>L. migratoria</i> by interacting with the immune responses of the host, demonstrating that this fungal strain of <i>M. anisopliae</i> can be an efficient biocontrol agent against <i>L. migratoria</i>.