Isolation of multiple subspecies of Bacillus thuringiensis from a population of the European sunflower moth, Homoeosoma nebulella

Five subspecies of #Bacillus thuringiensis# were isolated from dead and diseased larvae obtained from a laboratory colony of the European sunflower moth, #Homoeosoma nebulella#. The subspecies isolated were #B. thuringiensis# subspp. #thuringiensis# (H la), #kurstaki# (H 3a3b3c), #aizawai# (H 7), #morrisoni# (H 8a8b), and #thompsoni# (H 12). Most isolates produced typical bipyramidal crystals, but the #B. thuringiensis#. subsp. #thuringiensis# isolate produced spherical crystals and the #B. thuringiensis# subsp. #thompsoni# isolate produced a pyramidal crystal. Analysis of the parasporal crystals by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the crystals from the #B. thuringiensis# subsp. #kurstaki# and #aizawai# isolates contained a protein of 138 kDa whereas those from #B. thuringiensis# subsp. #morrisoni# contained a protein of 145 kDa. The crystals from #B. thuringiensis# subsp. #thuringiensis# contained proteins of 125, 128, and 138 kDa, whereas those from #B. thuringiensis# subsp. #thompsoni# were the most unusual, containing proteins of 37 and 42 kDa. Bioassays of purified crystals conducted against second-instar larvae of #H. nebulella# showed that the isolates of #B. thuringiensis# subspp.#aizawai#, #kurstaki#, and #thuringiensis# were the most toxic, with 50% lethal concentrations (LCS 50s) of 0.15, 0.17, and 0.26 ug/ml, respectively. The isolates of #B. thuringiensis# subspp. #morrisoni# and #thompsoni# had LC 50s of 2.62 and 37.5 ug/ml, respectively. These results show that a single insect species can simultaneously host and be affected by a variety of subspecies of #B. thuringiensis# producing different insecticidal proteins. (Résumé d'auteur