Six subspecies of
Bacillus thuringiensisBerliner ( Bt) were grown in minimal medium with chitin as the sole carbon source for 6 days to obtain Btcell-free fermented broths, which were then evaluated for chitinolytic activity and tested against third-instar Aedes aegypti(L.) (Diptera: Culicidae) larvae. Bt pakistanishowed the highest chitinolytic activity (approximately >2700 mU/mL), Bt kurstakishowed the lowest activity (approximately <2000 mU/mL), and Bt thompsoni, Bt aizawai, Bt israelensis, and Bt alestishowed intermediate activities (approximately 21002400 mU/mL). Bt aizawaiand Bt thompsonibroths showed the highest toxicity (LC50) against third-instar A. aegyptilarvae (approximately <290 mU/mL). Bt kurstakibroth showed the lowest toxicity (approximately 420 mU/mL), while Bt pakistani, Bt israelensis, and Bt alestibroths showed intermediate toxicities (approximately 360460 mU/mL). A purified and biochemically characterized Bt aizawaichitinase and commercial chitinases (from Serratia marcescensBizio and Streptomyces griseusWaksman and Henrici) were evaluated and compared for synergistic effects on Bt israelensisspore-toxin complex against third-instar A. aegyptilarvae. The synergism factor value of Streptomyces griseusand Bt aizawaichitinases were >2 and approximately 1.4; synergism was not evident for the Serratia marcescenschitinase (synergism factor value approximately 0.9).