Deletion of egt is responsible for the fast-killing phenotype of natural deletion genotypes in a Spodoptera frugiperda multiple nucleopolyhedrovirus population

Abstract

A Nicaraguan population of Spodoptera frugiperda multiple nucleopolyhedrovirus, SfMNPV-NIC, includes fast-killing genotypes with deletions in the egt region. Four bacmid based recombinants were constructed to determine the role of egt in this phenotype. SfdelF bacmid encompassed the deletion found in the NIC-F genotype. Sfdel3AP2 bacmid was constructed using the deletion reported in SfMNPV-3AP2 (Missouri, fast-killing isolate), whereas Sfdelegt and Sfdel27 bacmids lacked the single genes egt and the adjacent sf27 gene, respectively. No significant differences were observed in occlusion body (OB) concentration-mortality metrics (LC(50) values) among the viruses. Larvae infected by NIC-B (a natural genotype with the largest genome), Sfbac (a bacmid with NIC-B genome) and Sfdel27 survived significantly longer than insects infected by NIC-F, SfdelF, SfMNPV-3AP2, Sfdel3AP2 or Sfdelegt. Fast-killing viruses produced ∼6-13-fold fewer OBs/larva compared to other viruses tested. We conclude that deletion/disruption of egt is responsible for the fast-killing phenotypes of naturally-occurring genotypes in SfMNPV populations from Missouri and Nicaragua.