Abstract: A comparative study on the toxicity and deterrence among crystal, spore and thuringiensin A of Bacillus thuringiensis against Helicoverpa armigera(Hübner) was carried out. The parasporal crystals of Btk HD-1 were highly toxic and feeding deterrent to H. armigera larvae. The spores of Btk HD-1 showed some insecticidal activity and highly feeding deterrence. The spores of a HD-1 mutant without crystal, Cry-, had no toxicity and feeding deterrence. The thuringiensin A greatly inhibited larval development, but had no feeding deterrence. In the no choice test, larval feeding was arrested by HD-1 crystals, but HD-1 spores, mutant Cry- spores and thuringiensin A had no effect on larval feeding during the 45 min observation. When the crystal-spore mixture is combined with thuringiensin A, larval mortality was greatly increased.

Key words: Helicoverpa armigera, Bacillus thuringiensis, toxicity, deterrence