Nucleopolyhedrovirus enhancement by a fluorescent brightener in Mythimna separata (Lepidoptera: Noctuidae)

The fluorescent brightener Tinopal UNPA-GX enhanced the infectivity of a Mythimna separata nucleopolyhedrovirus (MyseNPV) in Mythimna separata (Walker) (Lepidoptera: Noctuidae) when larvae were perorally inoculated with a mixture of 1% of this brightener and occlusion bodies of MyseNPV. However, the infectivity was not enhanced when M. separata larvae were injected with a mixture of 1% Tinopal UNPA-GX and budded viruses of MyseNPV, suggesting that Tinopal UNPA-GX acts in the gut, not in the hemocoel. Peroral ingestion of Tinopal UNPA-GX resulted in a quick degradation of the midgut peritrophic membrane (PM) in M. separata larvae. Twenty-four hours after ingesting Tinopal UNPA-GX, the PM was fully regenerated. In addition, larval susceptibility to MyseNPV one day after ingesting the brightener did not differ significantly from that of larvae inoculated with the virus alone. These results suggest that Tinopal UNPA-GX facilitates the infectivity of MyseNPV by altering the structural integrity of the PM.