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Baculovirus infection of the armyworm (Lepidoptera: Noctuidae) feeding on spiny- or smooth-edged grass (Festuca spp.) leaf blades

Keathley, Craig P., Harrison, Robert L., Potter, Daniel A.
Biological control 2012 v.61 no.2 pp. 147
Festuca arundinacea, Nucleopolyhedrovirus, Pseudaletia unipuncta, biological resistance, cultivars, death, frass, friction, genes, grasses, infection, instars, leaf blade, nucleotide sequences, peritrophic membrane, plant spines, polymerase chain reaction, scanning electron microscopes, virion, Kentucky
Susceptibility of the armyworm, Mythimna unipuncta (Haworth), to infection by a baculovirus (NPV) isolated from a Kentucky armyworm population was compared on two suspected progenitors of tall fescue, Festuca mairei and Festuca arundinacea subsp. fenas, with spiny leaf margins intact or removed to test whether leaf spines abrade or puncture the peritrophic matrix (PM) and facilitate passage of virions to infection sites in midgut tissue. PCR amplification and sequencing of selected genes from the virus and phylogenetic inference from aligned sequences were carried out to identify and classify the virus. Edge spines had no effect on percentage infection or days to death of newly molted 5th instars fed spiny- or smooth-edged F. mairei leaf blades for 24h before and after droplet feeding doses of 10⁸ or 10⁹OBsml⁻¹. Fifth instars fed spiny- or smooth-edged grass blades had similarly undamaged PMs when viewed by scanning electron microscope. Fourth instars fed virus-treated F. arundinacea subsp. fenas leaf blades with spiny edges intact or removed did not differ in proportion infected or days to death. The food bolus moves in a liquid medium within the PM, and frass dissections showed that edge spines were often located inside a food bolus separated from the PM by non-spiny plant material rather than contiguous with the PM; therefore, friction of edge spines with the PM may have been low. These results suggest that armyworms will not be less susceptible to baculovirus infection when feeding on tall fescue cultivars with smooth leaf edges planted for improved livestock performance compared with those feeding on standard spiny-edged cultivars. We believe this to be the first study to investigate the effects of a natural physical structure on disruption of the PM and infection by a baculovirus.