Four novel Bacillus thuringiensis strains, which are deposited at the BCCM-LMG under accession nos. LMG P-12592, LMG P-12593, LMG P-12594, and LMG P-13493, produce new crystal proteins during sporulation that are toxic to Lepidoptera, more particularly against Noctuidae such as Spodoptera spp. and Agrotis ipsilon, against Pyralidae such as Ostrinta nubilalis, and against Yponomeutidae such as Plutella xylostella, and that are encoded by a novel gene. The crystal proteins contain protoxins, which can yield a toxin as trypsin-digestion product. A plant, the genome of which is transformed with a DNA sequence that comes from either one of the strains and that encodes its respective toxin, is resistant to Lepidoptera. Each strain, itself, or its crystals, crystal proteins, protoxin or toxin can be used as the active ingredient in an insecticidal composition for combatting Lepidoptera.