The Occurrence of Microsporidiosis (Nosema sp.) Infecting Helicoverpa armigera in Field and Its Pathogenicity

The occurrence of microsporidiosis(Nosema sp.) infecting Helicoverpa armigera was investigated in the field.In 2000,Helicoverpa armigera occurred servious,and microsporidiosis showed epidemic trend in its population.The infection rate of the 4th generation larvae was 49.0%.After 2001,the infection rate decreased gradually.The microsporidian could infect H.armigera,Pieris rapae and Spodoptera exigua and couldn′t infect Lencania separata,Ostrinia furnacalis and Bombyx mori.The pathogenicity had strong to Helicoverpa armigera.The microporidian with the concentration of 107 spores/mL could control previous generation population and keep down next generation population.The mortality of the 2nd instar larvae was 100% at 16 d after inoculation.The mortality of the 3rd instar larvae was 87.8% at 16 d after inoculation.When the microporidian with the concentration of 105 and 106 spores/mL inoculated the 2nd instars larvae,the eclosion rates were 32.2% and 13.3%,the mortalities of next generation larvae was 88.9% and 100%.The microporidian was useful to control the next generation population of H.armigera.