Author
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MARTIN, PHYLLIS |
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Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/25/2003 Publication Date: 6/1/2004 Citation: Martin, P.A. 2004. A stillbene optical brighterner can enhance bacterial pathogenicity to gypsy moth and colorado potato beetle. . Interpretive Summary: Gypsy moths are a major pest on oak and related trees in the spring and Colorado potato beetles can devastate potato fields. Bacterial diseases affect both these insects, but increasing how fast they kill would lessen the damage the insects do to the trees or crops. Optical brighteners (normally found in laundry detergents) increase the potency of insect viruses. We tested one optical brightener, Tinopal LPW, against four different bacteria (Bacillus thuringiensis, Serratia marcescens, Photorhabdus luminescens and Chromobacterium sp.) that kill either gypsy moth or Colorado potato beetle. For the bacteria (B. thuringiensis) which kill gypsy moth and for all four bacteria which kill Colorado potato beetle, the combination with optical brightener enhanced the total kill as well as the speed of kill of the pest insects. The addition of optical brightener greatly improved the toxicity of the least toxic bacteria, but only slightly improved the toxicity of the most toxic bacteria. Bacteria which did not kill gypsy moth were not affected by addition of optical brightener. Similar to optical brightener-virus combinations, the optical brightener-bacterial combinations also reduced the time to kill the pest. Thus, only particular combinations of this optical brightener and bacteria enhanced toxicity toward these pest insects while other combinations did not. Since optical brighteners also protect insect viruses and bacteria from ultraviolet light, producers of insect-toxic bacteria can use this optical brightener to improve the toxicity of their product to control insect pests. Scientists can also use optical brightener-bacterial combinations to make bacteria more effective against pest insects. Technical Abstract: Stilbene optical brighteners, which can protect biological control agents such as viruses, fungi, and nematodes against ultraviolet light, are known to enhance the activity of insect viruses in Lepidoptera. One stilbene optical or fluorescent brightener, Tinopal LPW, also enhances the activity of bacterial pathogens in gypsy moth and Colorado potato beetles by as much as 10-fold. This enhancement, however, did not occur for every bacterial-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, the addition of Tinopal LPW increased larval mortality with all pathogens tested (B. thuringiensis , Serratia marcescens, Photorhabdus luminescens, and Chromobacterium sp.). The brightener also decreased the LT50 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 enhancement of bacterial toxicity by fluorescent brighteners is compatible with mechanisms proposed for enhancement based on viral/lepidopteran/fluorescent brightener systems. |
