Abstract: The multiple nucleopolyhedrovirus of Spodoptera exigua (SeMNPV) forms the basis fora number of highly effective biological insecticides. To assess the prevalence and diversity ofSeMNPV genotypes in natural S. exigua populations, field populations were subjected to molecularanalyses. The genotypes associated with covert infections, that are likely to be verticallytransmitted, were compared to those associated with horizontally transmitted infections. Insightsinto the relationship between genetic diversity and transmission strategy were obtained bycomparing the genetic composition and insecticidal properties, of genotypes associated withvertically and horizontally transmitted infections. The results of these studies have clearapplications in the development of custom designed biopesticidal products without the need forrecombinant DNA technologies.