Effect of parasitism on a nucleopolyhedrovirus amplified in Spodoptera frugiperda larvae parasitized by Campoletis sonorensis

Abstract

We evaluated the consequences of parasitism by the solitary ichneumonid endoparasitoid Campoletis sonorensis (Cameron) towards the replication, genetic composition and virulence of a nucleopolyhedrovirus (Baculoviridae) originating from Spodoptera frugiperda (J. E. Smith) larvae. Parasitism by C. sonorensis and viral infection of third and fourth instar S. frugiperda larvae resulted in reduced growth compared with nonparasitized control larvae. A positive correlation was observed between virus yield and larval instar at the moment of infection. When larvae were virus-inoculated in the fourth instar, parasitism resulted in a significant reduction in mean per capita virus yield compared to the virus yield from nonparasitized larvae. In an experiment involving 10 serial passages of virus in both parasitized and nonparasitized larvae, restriction endonuclease analysis of viral DNA amplified in nonparasitized larvae revealed the presence of the wild-type virus as well as three additional variants (A, B, and C) diagnosed by the presence of novel submolar PstI fragments of different sizes. In contrast, analysis of viral DNA from parasitized larvae showed the presence of the wild-type virus and two other variants (E and F), each characterized by a different submolar BglII fragment. Southern blot analysis indicated that the submolar fragments of variants E and F contained sequences originating from the viral genome. Bioassay of the different virus variants in S. frugiperda larvae indicated that their virulence was equal or less than that of the wild-type virus. We conclude that parasitism can affect the quantity of virus produced in dually infected and parasitized larvae, but no adverse effects were detected in terms of the biological activity of the virus.