Classification, genetic variation, and biological activity of nucleopolyhedrovirus samples from larvae of the heliothine pests Heliothis virescens, Helicoverpa zea, and Helicoverpa armigera

A PCR-based method was used to classify 109 isolates of nucleopolyhedrovirus (NPV; Baculoviridae: Alphabaculovirus) collected worldwide from larvae of Heliothis virescens, Helicoverpa zea, and Helicoverpa armigera. Partial nucleotide sequencing and phylogenetic analysis of three highly conserved genes (lef-8, lef-9, and polh) indicated that 83 of these isolates were variants of the H. zea-H. armigera single nucleopolyhedrovirus (Hz/HaSNPV) species group. Twenty of the isolates were variants of a multiple NPV from H. armigera, HearMNPV. Four of the isolates were variants of Autographa californica MNPV (AcMNPV), and one isolate was a variant of Trichoplusia ni SNPV (TnSNPV). One sample from Colombia, South America contained three distinct NPVs, including an AcMNPV variant, a HearMNPV variant, and a previously undescribed NPV that grouped with a clade containing TnSNPV and Chrysodeixis chalcites NPV. In bioassays of a selection of isolates against H. zea, the commercially available Gemstar isolate of HzSNPV killed larvae faster than other Hz/HaSNPV isolates, and Hz/HaSNPV isolates killed larvae faster than HearMNPV isolates. Gemstar and the HearMNPV isolates exhibited higher LC50s than the other Hz/HaSNPV isolates tested.