ACTIVITY OF AN INSECTICIDAL PROTEIN FROM BACILLUS-THURINGIENSIS SUBSP THURINGIENSIS HD-290-1 STRAIN TO COLEOPTERAN AND LEPIDOPTERAN DEFOLIATORS OF POPLARS

In standardized laboratory bioassays, soluble protein extracted from Bacillus thuringiensis HD-290-1 was toxic to early larval instars of cottonwood leaf beetle, Chrysomela scripta F. (Chrysomelidae: Coleoptera) and forest tent caterpillar, Malacosoma disstria Hubner (Lasiocampidae: Lepidoptera) but was not toxic to first instars of fall webworm, Hyphantria cunea (Drury) (Arctiidae: Lepidoptera). Trypsin-digested toxin was slightly more toxic than undigested protoxin to cottonwood leaf beetles and forest tent caterpillars. Susceptibility of cottonwood leaf beetles decreased with increasing age (2- and 4-fold decrease in LC50 from first instars to third instars with protoxin and toxin, respectively). Adult cottonwood leaf beetle mortality did not exceed 30% when exposed to the highest dose of toxin tested (100 mug/ml for 96 h), but foliage consumption was decreased in a dose-dependent fashion. Adult beetles did not avoid leaf disks treated with B. thuringiensis extract in choice tests. These results are discussed with regard to genetic engineering of Populus with the gene coding for this protein.