Mamestra brassicae nucleopolyhedrovirus infection and enhancing effect of proteins derived from Xestia c-nigrum granulovirus in larvae of Mamestra brassicae and Helicoverpa armigera (Lepidoptera: Noctuidae) on cabbage.

The insecticidal effect of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) T5 against Mamestra brassicae (L.) and Helicoverpa armnigera (Hiibner) (Lepidoptera: Noctuidae), important pests of various vegetables and ornamental crops in Japan as well as many other countries, and the enhancing activity of proteins derived from occlusion bodies of Xestia c-nigrum granulovirus (XecnGV) a-4, which was named GVPs, on the infectivity of MabrNPV were evaluated in a bioassay with second-instar larvae fed on virus-applied cabbage, Brassica oleracea L. var. capitata, plants. The lethal concentrations of MabrNPV achieving 95% mortality (LC95) were estimated to be 7.7 x 10(5) and 1.8 x 10(5) OBs per ml for M. brassicae and H. armigera, respectively, with MabrNPV-alone treatment. Because the mean areas of cabbage leaf consumed by one larva in 60 h were not significantly different between M. brassicae and H. armigera, we conclude that MabrNPV is more infectious to H. armigera than to M. brassicae. When larvae were fed on cabbage plants treated with 10(4) OBs per ml MabrNPV and various concentrations of the GVPs, the mortality of the two noctuid larvae increased in relation to GVP concentration. The requisite concentrations of the GVPs achieving 95% mortality with the MabrNPV for M. brassicae and H. armigera were estimated to be 5.93-8.30 and 1.94-3.48 microg/ml, respectively. In a comparison of the MabrNPV-alone treatment with equivalent 95% mortality, addition of GVPs increased the rate of larval death at younger instars, especially in M. brassicae. Our results indicate that GVPs are a potentially useful additive for improving the insecticidal efficacy of MabrNPV.