Relative effectiveness of selected stilbene optical brighteners as enhancers of the beet armyworm (Lepidoptera : Noctuidae) nuclear polyhedrosis virus

The addition of a stilbene optical brightener, Tinopal LPW, at 1% concentration (wt:wt) significantly reduced the LC50 of the beet armyworm nuclear polyhedrosis virus (SeMNPV) from 2.9 PIB/mm2 to 0.02 PIB/mm2, Moreover, the LT50 of SeMNPV was reduced by 34% by the addition of Tinopal LPW. Seven other structurally related stilbene brighteners were also tested as viral enhancers. Five of these brighteners (Tinopal LPW, Blankophor BBH, Blankophor HRS, Blankophor P167, and Blankophor RKH) reduced LD50s, whereas three brighteners (Blankophor BSU, Blankophor DML, and Blankophor LPG) had little effect. Among the active brighteners, LC50s were reduced by 10.5-fold (Blankophor P167), 52.4-fold (Blankophor RKH), 87.3-fold Tinopal LPW), 131-fold (Blankophor BBH), and >400-fold (Blankophor HRS). LT50s were also decreased by the addition of Blankophor BBH, Blankophor P167, and Blankophor RKH, but were increased by the addition of Blankophor BSU, Blankophor DMLO, and Blankophor LPG to SeMNPV suspensions.