Abstract
Phylogenetic analyses suggest that Mamestra brassicae multiple nucleopolyhedrovirus (MbMNPV) and Helicoverpa armigera multiple nucleopolyhedrovirus (HearMNPV) may be strains of the same virus species. Most of the studies comparing their biological activities have been performed in their homologous hosts. A comparison of host range and stability in alternative hosts was performed. The host range of these viruses was compared using high concentrations of inoculum to inoculate second instars of six species of Lepidoptera. One semi-permissive host (Spodoptera littoralis) and one permissive host (S. exigua) were then selected and used to perform six serial passages involving a concentration corresponding to the ~25% lethal concentration for both viruses. Restriction endonuclease analysis showed fragment length polymorphisms in every host-virus system studied. In S. littoralis, serial passage of MbMNPV resulted in decreased pathogenicity and an increase in speed-of-kill, whereas no significant changes were detected for HearMNPV with respect to the initial inoculum. In contrast, both viruses showed a similar trend in S. exigua. These results highlight the low genetic diversity and a high phenotypic stability of HearMNPV with respect to the original inoculum after six successive passages in both insect hosts. This study concludes that host-baculovirus interactions during serial passage are complex and the process of adaptation to a novel semi-permissive host is far from predictable.
Highlights
The family Baculoviridae comprises double-stranded DNA viruses that are specific to invertebrate hosts
The mortality responses were similar for Mamestra brassicae multiple NPV (MbMNPV) and HearMNPV in all lepidopteran species tested, which resulted in two non-permissive hosts three
S. littoralis was selected were similar for the in allwhereas lepidopteran species which as the responses semi-permissive host for serial passage experiment, S. exigua wastested, selected as the resulted in two non-permissive hosts (L. botrana and O. nubilalis), one semi-permissive host
Summary
The family Baculoviridae comprises double-stranded DNA viruses that are specific to invertebrate hosts. Baculovirus classification based on the host from which the virus was isolated has obvious drawbacks for viruses that can productively infect multiple species of hosts. Viruses 2019, 11, 660 confusion when several baculoviruses are isolated from the same host species To address this issue, the International Committee on Taxonomy of Viruses (ICTV) determined that the definition of species status should involve phylogenetic criteria for lepidopteran specific baculoviruses, based on the genetic distances of the lef-8, lef-9 and polh/gran genes measured by the Kimura 2-parameter (K2P) value [4]. According to their genetic distance characteristics, Helicoverpa armigera multiple NPV (HearMNPV), Mamestra brassicae multiple NPV (MbMNPV) and Mamestra configurata NPV-B (MacoMNPV-B)
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