Serial Passage of aHelicoverpa armigeraNucleopolyhedrovirus inHelicoverpa zeaCell Cultures

Abstract

The serial passaging of baculoviruses in cell lines numerous times can result in a variety of mutations or defective viral populations becoming predominant in the cultures. The generation of these mutants during cell culture passage, also known as “the passage effect,” can seriously hinder the use ofin vitromethods for large-scale production of baculoviruses for use as biopesticides. In an effort to develop a large-scalein vitromethod of producingHelicoverpa armigerasingly enveloped nucleopolyhedrovirus (HaSNPV), it was essential to determine whether or not the passage effect was evident when this virus is serially passaged in cell cultures. An isolate of HaSNPV was serially passaged inHelicoverpa zeacell cultures up to 10 times. The production of occlusion bodies decreased with increasing passage number and there was evidence of defective viruses becoming predominant in cultures after 5 passages. The number of virions present within cross sections of passage 3 occlusion bodies was 1.5 times higher than those from passage 10 occlusion bodies when quantified using electron microscopy. A laboratory bioassay showed that potencies of passage 3 isolates againstH. armigeralarvae were 8 times higher than potencies of passage 10 isolates. This study indicated that changes typical of the passage effect were evident when HaSNPV was serially passaged inH. zeacell cultures up to 10 times.