Persistence and Effects of Parasitic Genotypes in a Mixed Population of the Spodoptera exigua Nucleopolyhedrovirus

Spod-X, a commercialized bioinsecticide for the control of the pest Spodoptera exigua, is based on a nucleopolyhedrovirus (NPV) of S. exigua (SeMNPV) isolated in Florida (US2wt). This field isolate is made up of at least seven genotypic variants, of which two (US2C and US2E) have defective genomes and act as parasites, reducing the pathogenicity of the viral population. Upon co-infection of US2wt and a Spanish field isolate of the same virus (SP2wt), persistence of the defective variants (US2C, US2E) in the viral progeny was observed. This persistence diluted the presence of intact, self-infectious genotypes in the progeny, decreasing the pathogenicity of these viral inocula. Further passages of viral occlusion bodies produced after the co-infection revealed that the parasite US2C continued replicating and constituted up to 30% of the viral progeny in some samples. In addition, the presence of US2C within SP2wt significantly decreased the pathogenicity of contaminated inocula by 3.6-fold. The use of foreign virus field isolates containing defective genomes and their possible impact on the biological activity of native NPV populations may be a cause for concern where these viruses are used as agents for biological control.