Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2005
Publication Date: 8/2/2005
Citation: Blackburn, M.B., Domek, J.M., Gelman, D.B., Hu, J.S. 2005. the broadly insecticidal photorhabdus luminescens toxin complex a (tca): activity against colorado potato beetle and sweet potato whitefly.. Journal of Insect Science. 5:32. Interpretive Summary: Deployment of crops containing insecticidal proteins can reduce the use of chemical applications for insect control, but very few candidate proteins have been described, and these typically control narrow ranges of pest species. We have tested an insecticidal protein, called Tca, from the bacterium Photorhabdus luminescens against both the Colorado potato beetle and the sweet potato whitefly, and found that it was highly effective against both of these very different pest species. We also determined that several parts of Tca were not required for the protein to remain active, perhaps leading to smaller versions of Tca that might be more easily produced by a plant. Tca and similar proteins from other bacteria may provide broad-spectrum insecticidal activity, and delay the possible development of resistance to Bacillus thuringiensis in the next generation of insect resistant crops. These results will be used by scientists developing these new insect resistant crops.
Technical Abstract: Toxin complex a (Tca), a high molecular weight insecticidal protein complex produced by the entomopathogenic bacterium Photorhabdus luminescens, has been found to be orally toxic to both the Colorado potato beetle, Leptinotarsa decemlineata, and the sweet potato whitefly, Bemisia tabaci biotype B. The 48 hour LC50 for Tca against neonate L. decemlineata was found to be 2.7 ppm, and the growth of 2nd instar L. decemlineata exposed to Tca for 72 hours was almost entirely inhibited at concentrations above 0.5 ppm. B. tabaci was highly susceptible to Tca as well; newly emerged nymphs that were artificially fed Tca developed poorly, or not at all. Tca concentrations between 0.1 and 0.2 ppm reduced the number of nymphs reaching the second instar by 50%. In addition, a preparation of Tca missing two prominent subunits, TcaAii and TcaAiii, was found to be at least as toxic as Tca itself, indicating that these subunits are not directly involved in oral toxicity to L. decemlineata or Bemisia tabaci.