SPODOPTERA-LITTORALIS (LEPIDOPTERA, NOCTUIDAE) RESISTANCE TO CRYIC AND CROSS-RESISTANCE TO OTHER BACILLUS-THURINGIENSIS CRYSTAL TOXINS

Laboratory selection of a strain of Spodoptera littoralis Boisduval wi th spore-crystal preparations of the Bacillus thuringiensis CryIC toxi n for 14 generations resulted in resistance ratios from 10- to >500-fo ld resistance by using 2 different methods of selection. Partial cross -resistance was exhibited to CryID, CryIE, CryIAb toxins and to the pa rental strain B. thuringiensis aizawai 7.29. No cross-resistance occur red to CryIF. Resistance declined from >500 times the resistance ratio to >74 times after 1 generation without selection pressure, remained approximate to 100 times after 3-6 generations and fell to 11 times af ter 8 generations. Sex ratio remained the same over selection period. Pupal weights of the selected strain varied, but we observed no trend in these differences. Developmental time increased from 5 to 6 d for t reated, resistant insects.