Fluorescence and relative activities of stilbene optical brighteners as enhancers for the gypsy moth (Lepidoptera: Lymantriidae) baculovirus

Eight structurally related stilbene optical brighteners were compared as enhancers for the gypsy moth nuclear polyhedrosis virus (LdNPV). Five of the 8 brighteners acted as activity enhancers (Blankophor HRS, P167, BBH, RKH, and Tinopal LPW); but Blankophor BSU, DML, and LPG did not enhance the activity of LdNPV. The most effective brighteners (BBH, RKH, and LPW) reduced LC(50)s from 800- to 1,300-fold. LT(50)s were influenced by some brighteners (HRS, LPW, BBH, RKH) but not by others (LPG, DML, BSU). All 8 brighteners exhibited fluorescence, which was concentration dependent. The most fluorescent brighteners were LPW, BBH, RKH, and P167, and the least fluorescent brighteners were LPG and DML. In general, the most active brighteners (i.e., those exhibiting the greatest viral enhancement) tended to exhibit the greatest fluorescence, and the least active brighteners tended to exhibit the least fluorescence. Although pHs of the brighteners ranged from 7 to 10, no correlation was found between pH and activity enhancement.