Viral-enhancing activity of various stilbene-derived brighteners for a Spodoptera litura (Lepidoptera: Noctuidae) nucleopolyhedrovirus

Previous reports have shown that stilbene-derived optical brighteners enhance viral activity in some baculovirus–lepidopteran host systems. To investigate the relationship between chemical structure and enhancement activity, we synthesized 11 stilbene-derived brighteners and compared their enhancing activity with a nucleopolyhedrovirus (NPV) with that of Tinopal UNPA-GX in common cutworm larvae, Spodoptera litura. Tinopal UNPA-GX significantly increased larval susceptibility to NPV infection, and the LD50 of NPV was reduced about 2200-fold by the addition of 1% Tinopal to the virus suspension. Five of the 11 brighteners enhanced NPV infection to a similar extent as Tinopal, and one brightener enhanced virus infection more effectively than Tinopal. Replacing the diethyl amino group of Tinopal UNPA-GX with other chemical groups changed the enhancing activity of the brighteners. In addition, disruption of the peritrophic membrane (PM) was observed only when the cutworm larvae were given brighteners that had viral-enhancing activity. This suggests that brighteners disrupt the PM that lines the insect midgut and facilitate NPV infection of midgut epithelial cells.