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

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 Sfde127 bacmids lacked the single genes egt and the adjacent sf27 gene, respectively. No significant differences were observed in occlusion body (OB) concentration-mortality metrics (LC50 values) among the viruses. Larvae infected by NIC-B (a natural genotype with the largest genome), Sfbac (a bacmid with NIC-B genome) and Sfde127 survived significantly longer than insects infected by NIC-F, SfdelF, SfMNPV-3AP2, Sfdel3AP2 or Sfdelegt. Fast-killing viruses produced, similar to 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. (C) 2012 Elsevier Inc. All rights reserved.