Efficacy of spiracular infection of Helicoverpa armigera with its nucleopolyhedrovirus and its role in virus production

Baculoviruses are important microbial control agents of insects, with per os mode of infectivity. However, recently the spiracular infection of this virus group was suggested as an optimum method for virus production in grown up larvae. In this regard, a detailed evaluation of the spiracular infection with intact polyhedral inclusion bodies (PIB), alkali liberated virions and alkali liberated filtered virions of Helicoverpa armigera (Hubner) nucleopolyhedrovirus at 1 × 108, 1 × 107 and 2 × 106 PIB/ml concentrations was undertaken and compared with the standard diet surface treatment method. All the spiracle treatments resulted in larval death due to virus infection with alkali liberated virions causing higher mortality of larvae than alkali liberated filtered virions and intact PIB. Diet surface treatment method resulted in very high mortality as compared to spiracle treatment and among the different inoculum tested the intact PIB resulted in higher larval mortality. The PIB yield/larva in spiracle treatment was comparable with the diet surface treatment method, but due to very low larval mortality it resulted in low virus yield/100 inoculated larvae. Diet surface treatment with 5 × 107 PIB/ml concentration of virus resulted in the maximum yield of PIB/100 inoculated larvae. Low mortality, higher labour requirement and low amenability for mechanization for spiracle treatment method make it unviable for mass production of the virus in large scale compared to the standard diet surface treatment method.