A laboratory method to evaluate the effectiveness of ultraviolet (UV) protectant for Bacillus thuringiensis product

Abstract

A laboratory method to evaluate the effectiveness of ultraviolet (UV) protectant for Bacillus thuringiensis (Bt) product (Esmark-DF WDG) was investigated using a commercial fluorescent lamp (FL20S·E, peak 315 nm: ranges 270-370 nm) and bioassay with the silkworm, Bombyx mori. A one-litter solution (1 g/1,000 ml) of Bt product was prepared in a glass beaker and exposed to fluorescent lamps at 5 cm below for 1-4 days. The bioactivity of irradiated Bt solution against the 2nd instar of silkworms was measured based on larval growth inhibition using the diet incorporation method. Percent growth inhibition was calculated by comparing weight gains of survivors at three days between the irradiated and non-irradiated solutions. The bioactivity of Bt solution was clearly decreased according to the exposure periods of fluorescence lamps. UV protective activity of iron oxide black (Fe3O4) for Bt solution was examined in the same manner and confirmed that it possessed effective UV protective activity dose-dependently. When 0.1% iron oxide black was mixed with Bt solution (1 g product/1,000 ml), it could reduce the inactivation from UV irradiation by 1/10 as compared to without it.