Optical brightener Tinopal C1101 as an ultraviolet protectant for a nucleopolyhedrovirus

Baculoviruses are arthropod-specific viruses currently used as biological insecticides in several countries of the world. One important factor limiting the efficacy of these bioinsecticides is related to the inactivation of the virus by solar ultraviolet (UV) radiation. This has motivated studies focused on the use of optical brightener compounds that can protect the virus from UV inactivation. The effects of the optical brightener Tinopal C1101 (ethenedyl benzenesulfonic derivative) on the persistance of a nucleopolyhedrovirus (SfMNPV) was quantified in third instar Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), the principal pest of maize in the Americas. For this, laboratory studies were performed to determine the relationship between virus concentrations and radiation-caused inactivation of SfMNPV alone or in mixtures with 1.25 or 0.1% (vol/vol) Tinopal C1101 using a UV system [radiation was provided by a 15 W UV tube (emission maxima at 312 nm)]. SfMNPV alone was more sensitive to UV than in mixtures with 1.25 or 0.1% Tinopal C1101. For instance, at concentrations of 2.22 x 10(8) and 2.75 x 10(6) occlusion bodies (OBs)/ml, SfMNPV alone-caused mortality was reduced from 88 and 44% (without UV radiation) to 0%, in both cases, after 30 and 15 min exposure to the UV tube, respectively. In contrast, the incorporation of 1.25% Tinopal C1101 into the SfMNPV inoculum at 2.22 x 10(8) and 2.75 x 10(6) OBs/ml caused a mortality of 86.6 and 96.6% after 240 min, respectively. UV-caused inactivation of SfMNPV was directly related to the optical brightener concentration. We conclude that optical brighteners are likely to represent valuable components of nucleopolyhedrovirus formulations.