Improvement in UV resistance of entomopathogenic viruses by coating silica nanoparticles on occlusion bodies surface

Entomopathogenic viruses, such as baculoviruses and cypoviruses, have been employed as biological pesticides against agricultural and forestry pests. However, their susceptibility to inactivation under field UV radiation has hindered their broader application. In this study, we effectively improved the UV resistance of insect virus occlusion bodies (OBs) by coating their surfaces with silica nanoparticles (SiO₂ NPs). Monodisperse SiO₂ NPs with uniform size distribution and excellent colloidal stability were synthesized using the Stöber method. Subsequent amination modification of the SiO₂ NPs with a silane coupling agent shifted their isoelectric point from 3.2 to 8.1. This modification imparted a strong positive charge to the NPs within the pH range of 4.5-5.5, while the OBs of insect viruses remained negatively charged in this range. Consequently, the amino-functionalized SiO₂ NPs were successfully coated onto the surfaces of OBs of three representative insect viruses: nucleopolyhedrovirus, granulovirus, and cypovirus, through electrostatic interactions. Laboratory bioassays confirmed that Mamestra brassicae multiple nucleopolyhedrovirus (MbMNPV) coated with SiO₂-NH₂ NPs retained its native viral pathogenicity against Spodoptera exigua larvae under normal laboratory condition, while it demonstrated 2.299-2.712 folds higher potency than MbMNPV physically mixed with unmodified SiO₂ NPs after UV irradiation. Outdoor trials revealed that SiO₂-NH₂ NPs coating significantly improved the survival time of MbMNPV, with the median survival time increased from 1.43 days to 5.15 days. This nanoparticle coating strategy establishes a robust platform for developing photostable biopesticides while preserving their ecological safety profiles. The modular nature of this approach suggests its broad applicability across different entomopathogenic virus formulations.