BACILLUS-THURINGIENSIS VAR KURSTAKI ACTIVITY AGAINST LARVAE OF HELICOVERPA-ZEA AND HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE) ON COTTON

Effectiveness of Bacillus thuringiensis (Javelin WG) against first instars of Helicoverpa zea (Boddie) and Heliothis virescens (F.) was studied in the laboratory on cotton terminals and in the field on cotton. In the laboratory, percentage mortality of both species increased significantly as the B. thuringiensis rate increased. Mortalities of H. virescens were significantly higher than H. zea at 0.56 and 1.12 kg/ha rates of B. thuringiensis at 4 and 7 d and pupation, respectively. Most mortality (60-91% in H. zea for H. virescens at 4 and 7 d and pupation, respectively. Most mortality (60-91% in H. zea and 76-98% in H. virescens) occurred by 4 d after treatment. Mortalities at the 8.96 kg/ha B. thuringiensis rate were similar to cypermethrin at 0.05 kg(AI)/ha in H. virescens for all dates and for 7 d and pupation H. zea. In the field, survival in both species generally decreased as B. thuringiensis rate increased. Survival was significantly higher in H. zea than in H. virescens at 1.12 and 2.24 kg/ha rates of B. thuringiensis at 3 and 7 d after treatment.