Abstract: AsNPV was mixed with HasNPV, HaNPV and PsNPV separately and thethree mixtures were used to infect the larvae of Helicoverpa assulta, H. arrnigera and Pseudaletia separata respectively. The nuclear polyhedrosis viruses thus obtained were called ( AsNPV+HasNPV) -H. assulta, (AsNPV+HaNPV) -H. armigera and (AsNPV+PsNPV) -P. separata respectively. The polyhedra of the NPVs were in irregular shape and varied distinctly in sizes. The biochemical charcaters of the viruses were investigated andcompared with those of HasNPV, HaNPV and PsNPV. The polyhedrin and viral structural polypeptides of the NPVs were examined by using SDS-PAGE. The polyhedrin of all NPVs had molecular weight of about 25 000 dalton. The numbers of the viral structural polypeptides of (AsNPV+HasNPV)-H. assulta, (AsNPV+HaNPV)-H. armigera and (AsNPV+PsNPV) -P. separata were 10, 14, 5 respectively, and their molecular weights were 13 500-98 000, 13 000-88 000, 18 500-52 000 dalton. The analysis of agarose electrophoretic profiles of DNAs restriction endonuclease fragments showed that they were notidentical to those of AsNPV, HasNPV, HaNPV and PsNPV. The DNAs of the viruses had changed and resulted in the changes of viral proteins and viral morphogenesis. Agrotis segetum nuclear polyhedrosis virus (AsNPV) can enhance the infection of HasNPV, HaNPV and PsNPV. The enhancement mechanism of AsNPV is worthwhile to be further investigated.

Key words: nuclear polyhedrosis virus (NPV), Agrotis segetum, Helicoverpa assulta, He- licoverpa armigera , Pseudaletia separata , mixed infection, enhancement