[lemma=□] □
[lemma=b] □
[lemma=t] □
B. t. formulations and different B. t. strains obtained from overseas culture collections or isolated from material collected in Kenya were screened for activity against C. partellus . Generally , low levels or control were obtained , which is probably due to the relatively narrow host range of the B. t. strains used . In the screenhouse trials all of the B. t. treated plants showed reduced levels of damage and yields were 5 to 7 times higher than the yield obtained from the untreated , infested control plots . Their identity as B. t. strains was confirmed by their growth characteristics , morphology and presence of a parasporal delta-endotoxin crystal .