| Abstract: | Stilbene optical brighteners were first investigated to protect biological control agents such as viruses, fungi, and nematodes against ultraviolet light. Some are known to enhance the activity of insect viruses in Lepidoptera. In this work, one stilbene brightener, Tinopal LPW, also increased mortality of gypsy moth and Colorado potato beetle larvae when treated with bacteria/optical brightener combinations. This increase in mortality, however, did not occur for every bacteria/insect combination. In gypsy moth, a significant increase in larval mortality was observed only with Bacillus thuringiensis combined with Tinopal LPW. In Colorado potato beetle, however, the addition of Tinopal LPW increased larval mortality with all bacteria tested (B. thuringiensis, Serratia marcescens, Photorhabdus luminescens, and Chromobacterium sp.). The brightener also decreased the time to kill for these pathogens. This decrease in LT50 was observed not only for bacteria+Tinopal LPW combinations, but also for combinations of Chromobacterium sp. toxin+Tinopal LPW. The mechanism for increase in bacterial toxicity by optical brighteners is compatible with mechanisms proposed for enhancement based on viral/lepidopteran/optical brightener systems that are not dependent on replication. |
