A spatzle protein involved in the immune response of Neoseiulus barkeri (Acari: Phytoseiidae) against Beauveria bassiana

The predatory mite, Neoseiulus barkeri, is more tolerant to the entomopathogenic fungus, Beauveria bassiana, than small sap-feeding pests. Infection of insects by B. bassiana can induce insect innate immune response, and the spatzle protein (Spz), an important ligand of the insect Toll pathway, has been demonstrated to play an important role in insect innate immune defense system. Here, we investigated the infection process of B. bassiana on N. barkeri using scanning electron microscopy, and identified a Spz protein. The result showed that NbSpz-1 was expressed in all developmental stages of N. barkeri and its expression was up-regulated by B. bassiana infection. After knocking down the expression of NbSpz-1 by dsRNA, the tolerance of N. barkeri to B. bassiana was weakened, and the survival rate was reduced. Our results verified the potential role of the Spz protein in N. barkeri immune response against B. bassiana. This study enhanced our understanding on innate immune system of phytoseiid mite.