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

The nuclear polyhedrosis virus (NPV) from H. zea (HzSNPV) was the most active virus tested against cotton bollworm, Helicoverpa (Heliothis) zea (Boddie) larvae (LC50 = 130 PIB per 30-ml cup) followed by MNPVs from the celery looper, Autographa falcifera (Kirby), (AfMNPV; LC50 = 2,100 PIB per 30-ml cup), the MNPV from the bollworm, H. armigera (Hubner) (HaMNPV; LC50 = 4,800 PIB per 30-ml cup), the MNPV from the wax moth, Galleria mellonella (L.) (GmMNPV; LC50, = 6,500 PIB per 30-ml cup), and the MNPV from the alfalfa looper, Autographa californica (Speyer) (AcMNPV; LC50 = 7,500 PIB per 30-ml cup). The addition of a selected brightener (Tinopal LPW) reduced the LC50s for HzSNPV by 8.7-fold, for AfMNPV by 13.1-fold, for HaMNPV by 25.3-fold, for GmMNPV by 2.1-fold, and for AcMNPV by 50.0-fold. The addition of Tinopal LPW significantly decreased the LT50s by 31.3% (AfMNPV), 30.5% (HaMNPV), 34.9% (GmMNPV), 28.9% (AcMNPV) but only decreased the LT50 for HzSNPV by 4.5%. Despite the addition of Tinopal LPW, H. zea larvae infected with AfMNPV, HaMNPV, GmMNPV, and AcMNPV died 1.2, 4.3, 2.6, and 3.5 d, respectively, later than larvae infected with HzSNPV alone.