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Title: A CONSTRUCTED STRAIN OF BACILLUS THURINGIENSIS HAS NOVEL TOXICITY TO APHIDS, THRIPS AND MITES

Author
item TYRUINI, S.A. - FSUE STATE RES.
item Martin, Phyllis
item MESHKOV, Y.I. - FSUE
item JAKOVLEVA, I.N. - FSUE
item ZHUZHIKOV, D.P. - FSUE
item HASHIMOV, P.H. - FSUE
item DEBABOV, V.G. - FSUE

Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/2005
Publication Date: 6/5/2005
Citation: Tyruini, S., Martin, P.A., Meshkov, Y., Jakovleva, I., Zhuzhikov, D., Hashimov, P., Debabov, V. A constructed strain of bacillus thuringiensis has novel toxicity to aphids, thrips and mites. Atlanta, Ga June 5-9 2005. . American Society for Microbiology Meeting.

Interpretive Summary:

Technical Abstract: Protein crystals, or '-endotoxins, produced by strains of Bacillus thuringiensis are lethal to insects in several orders including Diptera (mosquitoes and flies), Lepidoptera (caterpillars) and Coleoptera (beetles). The '-endotoxin genes have also been expressed in plants for insect control. Strains of B. thuringiensis can exchange genes by conjugation. We took advantage of this method to construct new strains of B. thuringiensis that are toxic to multiple orders of insects. Strains isolated from a commercial source, B. thuringiensis var. kurstaki (lepidopteran active)and B. thuringiensis var. tenebrionis (coleopteran active), were genetically crossed. Transconjugants were screened for toxicity to 2nd instar Colorado potato beetle larvae. One progeny strain, T-2581 had higher toxicity (92.5% mortality to 2nd instar Colorado potato beetle) than the beetle-active parent (25.1% mortality at the same dose). When this strain was applied to potatoes under field conditions, there were not enough beetles present for a statistically valid test. However, the number of green peach aphids, secondary pests on potatoes both in the United States and Russia, was greatly reduced. This unexpected activity led to testing of this strain against a number of related greenhouse pests including thrips, mites, and whiteflies. The strain, T-2581, reduced numbers of thrips and mites, but not white flies. The activity against aphids appeared to be concentrated in the spore-crystal fraction and the activity against thrips in the supernatant. The two parent strains caused less than 18% mortality in aphids while the mortality caused by the progeny strain was 59.2%. For thrips, mortality caused by the two parent strains was less than 13% and the mortality caused by the progeny strain was 53.3%. On mites, the parent strain mortality was less than 24 %, while the progeny strain was 91.5%. Further field trials in Uzbekistan confirmed activity against aphids, thrips, and mites. This B. thuringiensis strain reduced the numbers of aphids slower than the recommended chemical control, carbophos (malathion) an organophosphate. By day 10 for green peach aphid on roses, the B. thuringiensis strain outperformed the chemical. Control against aphids was equivalent for this pest on both cotton and lemon crops. This is the first known case of a biological controlling not only the primary crop pest, but the secondary pests that appear after application.