Novel nanoparticle formulations improve the tolerance of Metarhizium brunneum to ultraviolet radiation and biocontrol efficacy against Frankliniella fusca (Thysanoptera: Thripidae).

Oil-in-water Pickering emulsions stabilized by titania (TiO2) nanoparticles have shown potential to increase ultraviolet (UV) protection in the entomopathogenic fungus Metarhizium brunneum. In this study, we expand the findings by comparing several nanoparticle-based formulations for UV tolerance, and investigating the impact of protective formulations in a biocontrol setting. The fungal viability in colony forming units (CFUs) and virulence to the 2nd instar tobacco thrips, Frankliniella fusca, were assessed. Under UV-A (380-nm), a titania-based formulation was effective in protecting the fungal viability at 6-h exposure but not at 12-h; silica (SiO2) did not provide any UV protection. UV-A radiation for up to 12 h did not reduce the fungal virulence in any treatment; then a stronger UV treatment was warranted. Under UV-C (254-nm), silica was ineffective in improving the viability or virulence of M. brunneum. The titania-based emulsion showed partial protection for up to 10-min exposure, with 51-56% reduction in CFU counts compared to nearly 100% reduction in the control, while it only exhibited marginal effect in assessing fungal virulence. Two titania-based formulations (titania-MO-1 and titania-PO-2) were further explored for enhanced UV tolerance. Titania- MO-1 had fewer CFUs at 10-min UV compared to control; titania- PO-2 showed no reduction in fungal viability. The two titania formulations were equally effective in maintaining fungal virulence to F. fusca regardless of UV exposure. Overall, titania nanoparticles (particularly titania- PO-2) protected M. brunneum conidia against UV radiation, suggesting the potential use of titania nanoparticles in formulating M. brunneum for improved UV tolerance and biocontrol potential.