Specificity of Ukrainian Bacillus thuringiensis Berliner Strains for Agricultural Pests of the Southeastern United States

Abstract

Insecticidal proteins naturally produced by Bacillus thuringiensis Berliner (Bt) present an environmentally friendly alternative to the conventional chemicals used for the pest control. We identified crylA, crylB, and cry1C genes encoding the toxic proteins in 13 Bt strains isolated in Ukraine and then determined the toxicity of these strains against lepidopteran and coleopteran pests from the southeastern U.S. Five of the Bt strains were highly toxic to two lepidopteran pests: three against the soybean looper (Pseudoplusia includens Walker), and two others against the cabbage looper (Trichoplusia ni Hübner). None of the strains had more than moderate toxicity against the tobacco budworm (Heliothis virescens F.), the sugarcane borer (Diatraea saccharalis F.), or fall armyworm (Spodoptera frugiperda J.E. Smith). Cry1 toxins from three Bt strains were solubilized and trypsinized for bioassay against the boll weevil (Anthonomus grandis grandis Boheman) and sweet potato weevil (Cylas formicarius Summers). Toxicity of all three strains was higher or comparable to that of the commercial Bt product Foil® (ECOGEN Inc., Langhorne, PA) containing Cry3 toxin specific for coleopterans. Two of the Ukrainian Bt strains containing Cry1B toxins were toxic to both lepidopteran and coleopteran pests. This study thus revealed new Bt strains toxic to lepidopteran and coleopteran pests from the southeastern U.S. indicating specific target pests for a broad spectrum of Cry1 toxins, including natural and trypsin-activated forms of CrylB proteins.