Silencing of selenium-binding protein disrupted the active immunization of the termite Reticulitermes chinensis and improved the lethal effect of the entomopathogenic fungus Metarhizium anisopliae

Active immunization is a process by which naive termites receive sublethal doses of pathogenic spores from infected termites through social contact to enhance their immune responses; this process significantly diminishes the termite biocontrol effect of commercial entomopathogenic products, such as Metarhizium anisopliae. We found that the expression of selenium-binding protein (SeBP) was significantly increased by active immunization of the nestmates of fungus-contaminated termites, suggesting a close relationship between SeBP and active immunization in termites. To elucidate this relationship, we used the fungus M. anisopliae to contaminate the termite Reticulitermes chinensis and then measured the changes in the grooming behavior, antifungal activity, immune gene expression and survival of the double-stranded SeBP (dsSeBP)-injected nestmates of these fungus-contaminated termites. Our results showed that there was no significant change in the grooming behavior of the dsSeBP-injected nestmates of the fungus-contaminated termites, but the antifungal activity and expression of the immune gene Gram-negative bacteria-binding protein 2 (GNBP2) were significantly reduced. Moreover, the survival of the dsSeBP-injected nestmates of the fungus-contaminated termites was significantly decreased. These findings showed that SeBP knockdown disrupted the active immunization of R. chinensis and improved the lethal effect of M. anisopliae, which suggested that enhancing immune dysregulation by targeting SeBP was a sound strategy for the biological control of termites.