Biological and genomic characterization of a novel gammabaculovirus for biocontrol of Diprion infuscalae (Hymenoptera: Diprionidae).

Diprion infuscalae Wang & Wei, an emerging sawfly pest of the Chinese red pine, Pinus massoniana, is currently endemic to Jiangxi and Fujian provinces within the mainland China. To mitigate its infestation and to reduce our reliance on chemical pesticides, a naturally occurring nucleopolyhedrovirus (DiinNPV), was isolated from the deceased D. infuscalae larvae. Bioassays confirmed its high virulence against D. infuscalae under laboratory conditions. DiinNPV was then characterized morphologically using electron microscopy and genetically through the whole-genome sequencing. Its occlusion bodies consist of irregularly shaped polyhedra, which contain multiple enveloped, rod-shaped virions, each with a single nucleocapsid. The 77,381 bp genome, with a 33.9% G + C content, is the smallest among baculoviruses. It encodes 83 open reading frames, including 38 core, 8 lepidopteran, 34 hymenopteran, and 3 DiinNPV specific baculovirus genes, along with 2 direct repeats and 4 homologous repeats. Phylogenetic analyses and Kimura-2-parameter distances identify DiinNPV as a novel gammabaculovirus, provisionally named Gammabaculovirus diprinfuscalae. Gene parity plot and Mauve analyses exhibit high collinearity with other gammabaculoviruses and highlight nonsyntenic regions with inversions and rearrangements between orf2 and orf30 in comparison to 2 other hymenopteran baculovirus, NeleNPV and NeabNPV. Our toxicity assays, together with morphological and genomic characterization, provide strong evidence for DiinNPV's potential as a biocontrol agent and support its integration into integrated pest management strategies against D. infuscalae.