Enhancing effect of proteins derived from Xestia c-nigrum granulovirus on Mamestra brassicae nucleopolyhedrovirus infection in larvae of Autographa nigrisigna (Lepidoptera: Noctuidae) on cabbage

The insecticidal effect of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) and the enhancing activity of proteins derived from occlusion bodies (OBs) of Xestia c-nigrum granulovirus (GVPs) on the infectivity of MabrNPV were evaluated in a bioassay with second-instar larvae of Autographa nigrisigna (Walker) fed virus-applied cabbage plants. The lethal concentrations of MabrNPV achieving 50 and 95% mortality for A. nigrisigna were estimated to be 1.4 × 105 and 3.1 × 106 OBs/ml, respectively. When larvae were fed cabbage plants treated with MabrNPV and various concentrations of GVPs, the requisite concentration of GVPs achieving 95% mortality of A. nigrisigna was estimated to be 26.2–138.8 μg/ml in combination with 104 OBs/ml MabrNPV and 8.46–24.09 μg/ml with 105 OBs/ml MabrNPV. Increases in the concentration of MabrNPV or GVPs caused larval death at younger instars. A. nigrisigna has lower susceptibility to MabrNPV than M. brassicae and Helicoverpa armigera reported in Mukawa and Goto (J Econ Entomol 103:257–264, 2010). We estimated that the requisite concentration of MabrNPV for the control of A. nigrisigna was 105 OBs/ml, which is a tenfold higher concentration than that for M. brassicae and H. armigera, with the increase achieved by adding 10 μg/ml GVPs.