Lethal Activity of Two Bacillus thuringiensis Strains against Haemonchus contortus Histotropic Larvae

The in vitro lethal activity of two Bacillus thuringiensis strains (IB-16 and IB-61) against Haemonchus contortus histotropic fourth stage larvae (L-4) was evaluated. Each B. thuringiensis strain was used as soluble proteins at different concentrations. In addition, the in vitro lethal dose (LD50) of each strain was determined against H. contortus L-4 at different times. Data were analyzed by ANOVA and Tukey tests. Less than 50% mortality was observed at 50 and 100 mu g/mL, during all bioassays. More than 50% mortality was observed at 200 mu g/mL at 3 and 5 days after interaction with IB-16 and IB-61, respectively. A 100% mortality was observed with IB-16 on day 5. The LD50 with IB-16 was 248 mu g/mL on day 3, and IB-61 showed an LD50 at 227 mu g/mL on the day 5. Both toxins may have potential as biocontrol agents.