Baculoviridae is a family of insect-specific DNA viruses that have been used as biological control agents for insect pest control. In most cases these baculovirus control agents are natural field isolates that have been selected based on their infectivity and virulence. The advent of molecular tools such as restriction endonucleases, targeted polymerase chain reaction and new DNA sequencing strategies have allowed for efficient detection and characterization of genotypic variants within and among geographic and temporal isolates of baculovirus species. It has become evident that multiple genotypic variants occur even within individual infected larvae. Clonal strains of baculovirus species derived either by in vitro or in vivo approaches have been shown to vary with respect to infectivity and virulence. Many of the cell culture derived plague-purified strains have deletions that interrupt egt expression leading to virus strains that kill infected hosts more quickly. As well, in vitro clones often involve larger genomic deletions with the loss of pif gene function, resulting in strains deficient for oral infectivity. There are an increasing number of baculovirus species for which complete genome sequences are available for more than one strain or field isolate. Results of comparative analysis of these strains indicated that hr regions and bro genes often mark "hot spots" of genetic variability between strains and of potential recombination events. In addition, the degree of nucleotide polymorphisms between and within strains and their role in amino acid substitutions within ORFs and changes in promoter motifs is also beginning to be appreciated. In this short review the potential mechanisms that generate and maintain this genetic diversity within baculovirus populations is discussed, as is the potential role of genetic variation in host-pathogen interactions.