Effects of stilbene optical brighteners on the insecticidal activity of Bacillus thuringiensis and a single nucleopolyhedrovirus on Helicoverpa armigera

• Published in: Biological control 2008-12, Vol.47 (3), p.322-327
• Main Authors: Ibargutxi, María A., Muñoz, Delia, Bernal, Alexandra, Escudero, Iñigo Ruiz de, Caballero, Primitivo
• Format: Article
• Language: English
• Subjects: Bacillus thuringiensis; Bacillus thuringiensis subsp. kurstaki; entomopathogenic bacteria; Helicoverpa armigera; Helicoverpa armigera nucleopolyhedrovirus; insect control; insect viruses; Insecticidal activity; lethal dose 50; Nuclear polyhedrosis virus; Nucleopolyhedrovirus; Optical brighteners; pathogenicity; pesticide formulations; stilbenes
• ISSN: 1049-9644; 1090-2112
• DOI: 10.1016/j.biocontrol.2008.08.019

The incorporation of certain stilbene optical brighteners into virus-based formulations has been demonstrated to increase viral pathogenicity (as indicated by reduced LD/LC 50 values) but their effect on Bacillus thuringiensis activity has been scarcely investigated. We determined the effect of nine optical brighteners on the insecticidal activity of B. thuringiensis ser. kurstaki HD-1 strain (Bt HD-1) on Helicoverpa armigera and also compared the effect of two optical brighteners on the insecticidal activity of Bt HD-1 and occlusion bodies (OBs) of a Spanish isolate of H. armigera single nucleocapsid nucleopolyhedrovirus (HearNPV-SP1). Blankophor CLE, Blankophor DRS, Blankophor ER, and Leucophor SAC significantly increased the pathogenicity of Bt HD-1. In contrast, Tinopal UNPA-GX, Tinopal CBS, Blankophor BA, Leucophor AP, and Leucophor UO had an adverse or no effect on its insecticidal activity. Mixtures of HearNPV-SP1 OBs with Tinopal UNPA-GX or Leucophor UO resulted in 31.4- and 11.4-fold increases in pathogenicity, respectively, at 1%, and 11.4- and 6.3-fold increases in pathogenicity, respectively, at 0.1%, compared to the OBs alone. However, none of these brighteners increased Bt HD-1 activity. These results appear consistent with the hypothesis that the enhancement of HearNPV-SP1 pathogenicity and the null or antagonistic effects observed in Bt HD-1 against H. armigera were due to optical brightener-mediated degradation of the peritrophic membrane, but additional systematic studies involving a broad range of brighteners and electron microscope observations are required to confirm this premise.