Lethal and sublethal effects of Bacillus thuringiensis Berliner ssp aizawai on Spodoptera littoralis Boisduval Lepidoptera Noctuidae larvae in extended laboratory tests Effetti letali e subletali di Bacillus thuringiensis Berliner ssp aizawai su larve di Spodoptera littoralis Boisduval Lepidoptera Noctuidae in prove di laboratorio esteso