Effects of cellulose fine particles as a delivery carrier on the structure of nuclear polyhedrosis virus occlusion bodies from Spodoptera litura nucleopolyhedrovirus (SlNPV) and Helicoverpa armigera nucleopolyhedrovirus (HearNPV)

Nucleopolyhedroviruses (NPVs) isolated from Spodoptera litura (SlNPV) and Helicoverpa armigera (HearNPV) were formulated with cellulose fine particles (CFPs) as a sustainable delivery system. Using mechanical bead-milling followed by sonication, microcrystalline cellulose was reduced to a high-surface-area fibrillar matrix with a mean particle diameter of 527 nm. Electron microscopy and EDS analysis confirmed that CFPs effectively associated with the surfaces of HearNPV and SlNPV occlusion bodies (OBs) without inducing structural deformities or matrix degradation, a critical advantage over smaller mineral-based nanoparticles. SEM observations demonstrated that CFPs preserved viral integrity, while statistical analysis of the bioassays indicated that the formulations maintained high pathogenicity. Bioassays demonstrated that S. litura larvae infected with the SlNPV+CFP formulation exhibited mortality rates exceeding 85%. Notably, exposure to CFPs alone induced up to 69% mortality, indicating that CFPs themselves affected larval survival. The lethal time for infected larvae ranged from 2.03 to 2.68 days, with the most rapid mortality (2.03 ± 0.02 days) observed in the SlNPV+ CFP group. This accelerated effect suggests that the SlNPV+CFP formulation may improve the performance of NPV-based bioinsecticides. These findings suggest that the SlNPV+CFP formulation offers a promising, environmentally friendly alternative to synthetic insecticides for the sustainable control of S. litura and potentially other lepidopteran pests.