Effect of proteins derived from granulovirus on the infectivity of Mamestra brassicae nucleopolyhedrovirus in Helicoverpa armigera (Lepidoptera: Noctuidae)

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The enhancing effect of virion-free proteins derived from granulovirus (GVPs) on the infectivity of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) was examined using an alternative host, Helicoverpa armigera (Hübner). Second-instar larvae were inoculated by diet contamination bioassay. The LC₅₀ values of larvae inoculated with MabrNPV alone were calculated to be 24,000 to 96,000 polyhedra/g diet, which was equivalent to the values of the original host, Mamestra brassicae (L.), in our previous report. The addition of GVPs (0.1 mg/g diet) reduced the LC₅₀ values to 1/13.8–1/38.4. Most MabrNPV-infected larvae died at the third or fourth instar, and the increase of MabrNPV concentration caused larval death at younger instars in both the MabrNPV alone treatment and the MabrNPV plus GVPs treatment. The lethal time shortened in relation to viral concentration for both the MabrNPV alone treatment and the MabrNPV plus GVPs treatment. Our results reveal the potential for simultaneous control of M. brassicae and H. armigera by adding GVPs as an enhancer to MabrNPV.