Tolerance of Steinernema carpocapsae infective juveniles in novel nanoparticle formulations to ultraviolet radiation

Entomopathogenic nematodes (EPNs) are susceptible to abiotic environmental factors including ultraviolet (UV) radiation, which affects the survival and efficacy. This study evaluated nanoparticle (NP) formulations for protecting Steinernema carpocapsae infective juveniles (IJs) from UV radiation. First, silica-NH2 NPs at oil-to-water ratios of 2:8, 3:7 and 4:6 were compared with Barricade Fire Gel (1% and 2%) and a water control (aqueous IJs) by exposing IJs to UV light (254 nm) for 0, 10 and 20 min. Barricade gel (especially 2% Barricade) significantly improved IJs viability after UV treatment, while all three NPs had adverse effects on IJs viability after UV radiation. Subsequently, two silica (SiO2 basic and advanced) and one titania (TiO2) based formulations were tested with Barricade (1% and 2%) and a water control. The titania-NH2 NPs provided the highest UV protection, and IJ viability and virulence were not reduced even after 20-min UV. Except TiO2, only 2% Barricade at 10-min UV and SiO2 basic at 20-min UV had lower IJ mortality than the water control. Only TiO2 formulated IJs caused higher insect mortality and infection levels than aqueous IJs after UV treatment. The UV tolerance of TiO2 was further examined by assessing the number of nematodes invading the hosts. Consistent with virulence tests, the number of invading nematodes in titania-NH2 NPs did not decrease after UV radiation for 10 or 20 min compared with the no-UV control. The anti-UV capability of titania-NH2 NPs has promise as a tool to enhance biocontrol efficacy of EPNs under field conditions.