Metarhizium anisopliae is an important class of entomopathogenic fungi used for the biocontrol of insects, but its virulence is affected by insect immunity. We identified a novel FK506 binding protein gene that was differentially expressed between control and Metarhizium-treated Locusta migratoria manilensis. We hypothesized that this protein played an important role in Metarhizium infection of L. migratoria and could provide new insights for developing highly efficient entomopathogenic fungi. We, therefore, cloned the specific gene and obtained its purified protein. The gene was then named FKBP52, and its dsRNA (dsFKBP52) was synthesized and used for gene interference. Bioassay results showed that the mortality of L. migratoria treated with dsFKBP52 + Metarhizium was significantly lower than that of other treatments. Furthermore, immune-related genes (MyD88, Dorsal, Cactus, and Defensin) in L. migratoria treated with dsFKBP52 + Metarhizium showed significant upregulation compared to that treated with Metarhizium only. However, the activities of peroxidase (POD), superoxide dismutase (SOD), and calcineurin (CaN) showed fluctuations.These results suggest that the FKBP52 gene may play a crucial role in the innate immunity of L. migratoria.The effect of its silencing indicated that this immunity-related protein might be a potential target for insect biocontrol.

Graphical Abstract

After feeding on FKBP52 protein, it was found that the survival rate of the FKBP52-only baits was 97.78% by day 10, which was not significantly different (P > 0.05) from the control (98.89%). When treated with M. anisopliae alone, the survival rate decreased with the number of days of treatment, reaching 40% by day 10, which was significantly lower than that of the FKBP52 protein alone and the control group. The survival rate of the locusts decreased rapidly when treated with FKBP52 protein and M. anisopliae, reaching 6.67% by day 10, which was significantly lower than that of the M. anisopliae alone (P < 0.05).The above results showed that the co-treatment of FKBP52 protein and M. anisopliae significantly increased the pathogenicity and insecticidal effect of the treatment on the L. migratoria.

After injection of dsFKBP52, the bioassay results obtained under different treatments showed that injection of the dsFKBP52 killed only 5.56% of L. migratoria, and this was not different from that of the control.The survival rate was 98.89% on the 10th day. Application of M. anisopliae alone decreased the survival rate of L. migratoria to 26.67% on the 10th day after infection. This was significantly lower than that recorded from the injection of dsFKBP52 and the control. The survival rate recorded when M. anisopliae and dsFKBP52 were applied in combination was 64.44%.This was significantly higher than recorded under treatment of M. anisopliae treated alone (P < 0.05). The above results showed that the co-treatment of dsFKBP52 and M. anisopliae significantly enhanced the immune ability of L. migratoria and reduced the pathogenicity of M. anisopliae.