Abstract: Primary studies were designed to determine the effect of three fluorescent brighteners, Tinopal LPW, JD-3 and VBL, on the infectivity of Bacillus against neonates of Helicoverpa armigera. Furthermore, the fluorescent brightener VBL was tested as photodegradation for B. thuringiensis. The results showed that the LC ₅₀ of Bt declined from 1.23 to 2.00 fold with the addition of 10g/kg fluorescent brighteners. The magnitude of reduction in LC ₅₀ in H. armigera larvae indicated that selected brighteners enhanced the virulence of Bt insecticides in varying degrees. Moreover, the adjuvant VBL at different concentration provided effective protection when Bt was exposed to UV irradiation (i.e.>70% original activity remained).