Enhancement in activity of homologous and heterologous baculoviruses infectious to beet armyworm (Lepidoptera: Noctuidae) by an optical brightener

The nuclear polyhedrosis virus (NPV) from the beet armyworm, Spodoptera exigua (Hübner) (SeMNPV), was the most active virus tested against the beet armyworm (LC50 = 4.1 PIBs/mm2), followed by nuclear polyhedrosis viruses from the alfalfa looper, Autographa californica (Speyer) (AcMNPV; LC50 = 92.6 PIBs/mm2), and the celery looper, Anagrapha falcifera (Kirby) (AfMNPV; LC50 = 195.7 PIBs/mm2). In the case of the nuclear polyhedrosis virus from the bollworm, Helicoverpa armigera (Hübner), LC50s could only be obtained for five/six replicates, whereas LC50s could only be obtained for two/six replicates for the nuclear polyhedrosis virus from the wax moth, Galleria mellonella (L.) (GmMNPV). When an optical brightener Tinopal LPW was added to virus suspensions, LC50 values were reduced by 130-fold for both SeMNPV and AcMNPV and by 300-fold for AfMNPV. The addition of Tinopal LPW greatly increased the activities of HaMNPV and GmMNPV. In terms of speed of kill, Tinopal LPW reduced the LT50s for all nuclear polyhedrosis viruses by 30-40%.