Studies on Ultraviolet Protectants for Bacillus thuringiensis Product

Abstract

Ultraviolet (UV) protection of Bacillus thuringiensis (Bt) suspension by addition of iron(III) oxide (Fe 2 O 3 ) was investigated under laboratory conditions using a Bt product (Esmark-DF), a commercial fluorescent lamp (Toshiba-FL20S · E, peak 315 nm: ranges 270-370 nm) and a bioassay with the silkworm, Bombyx mori. Iron oxide was mixed at 0.01-0.1% into one litter of Bt suspension (1 g Bt product weight/ 1,000 ml water) in a glass beaker and exposed to fluorescent lamps at a distance of 5 cm for 1-4 days. The bioactivity of irradiated Bt suspension with and without iron(III) oxide was compared based on larval weight gains of the 2nd instar of silkworms over 3 days. The bioactivity of Bt suspension without iron oxide fell to 1/224 of the original level during 4 days' irradiation. On the other hand, Bt suspension with 0.1% iron(III) oxide maintained the same bioactivity as that of the original level, indicating good UV protection. UV protection was also observed at lower concentrations of 0.03 and 0.01% of iron(III) oxide, indicating bioactivity as 1/5 and 1/23 of the original, respectively.