Genetic Variation and Biological Activity of Two Closely Related Alphabaculoviruses during Serial Passage in Permissive and Semi-Permissive Heterologous Hosts

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.

Pathogenicity of nuclear polyhedrosis virus to Galleria mellonella L. (Lepidoptera: Pyralidae) and its control on stored beeswax foundations

“…As well, motionless due to infection of the nerve cells and alterations in tracheal epithelial cells lower and stop respiration leading to death of infected larvae. These results are in line with similar studies with MNPVs in larvae of different lepidopteran species, like those of El Husseini (1980) in Spodoptera exigua, Yan and Li (1991) in Dendrolimus spectabilis, Daibin et al (1999) in Zethenia rufescentaria, Barreto et al (2005) in Spodoptera frugiperda, and Wang et al (2017) in Bombyx mori and Belda et al (2019).…”

Coocclusion of Helicoverpa armigera Single Nucleopolyhedrovirus (HearSNPV) and Helicoverpa armigera Multiple Nucleopolyhedrovirus (HearMNPV): Pathogenicity and Stability in Homologous and Heterologous Hosts

“…Serial passage has been used as a tool to increase the insecticidal activity of alpha-and betabaculoviruses in semi-permissive hosts [61][62][63][64], although not all of these studies had molecular tools available to verify the identity of progeny OBs and rule out the possible activation of a latent infection in the heterologous host. A previous study of HearMNPV in two heterologous hosts (S. exigua and S. littoralis) indicated that this virus did not undergo marked changes in OB pathogenicity characteristics in either host during serial passage, although significant changes in speed of kill were detected in some lineages [39]. By contrast, serial passage at high inoculum concentrations was used to examine how the diversity of an indicator gene (dnapol) varied during the process of adaptation of a HearSNPV isolate in individual insects of the homologous host [65], or how changes in the relative prevalence of cooccluded genotypes affected the insecticidal phenotype in HearSNPV [66] and SfMNPV [67].…”

“…Isolates of HearSNPV have a narrow host range [35], which is limited to species in the genera Helicoverpa and Heliothis [22]. In contrast, isolates of HearMNPV show greater genetic diversity across geographical locations [27,36], and infect a broader range of hosts, including species outside of the Helicoverpa/Heliothis complex [37][38][39]. In this sense HearMNPV resembles the closely related broad host range NPVs from Mamestra brassicae (MbMNPV) and Mamestra configurata (MacoNPV-B) [30].…”

Evolutionary analysis and biological characterization of a novel alphabaculovirus isolated from Mythimna separata

“…MbMNPV and MacoNPV-B were considered to be different variants of the same baculovirus [7], and were highly similar in morphological and biological characteristics [17]. Erlandson [54] compared the morphology of MbMNPV and MacoNPV and found that both viruses were multi-particle embedded, with hexagonal or pyramidal polyhedrons of ~2.0-2.5 µm in diameter.…”

“…These isolates are named after the hosts from which they were isolated, but they are not listed or categorized by ICTV. In addition, the host range and infectivity of each MbMNPV variant were found to differ [16,17].…”