Bacillus thuringiensis alone and in mixtures with chemical insecticides against heliothines and effects on predator densities in cotton

Abstract

Tests were conducted in a cotton field in 1994 and 1995 to evaluate the efficacy of Bacillus thuringiensis var. kurstaki Berliner alone and in mixtures with thiodicarb and cyhalothrin against heliothines and to evaluate the survival of predators on cotton. The heliothine population treated in both years was almost entirely Helicoverpa zea (Boddie) (>97%). In both years, B. thuringiensis alone failed to reduce larval populations over the control plots (P > 0.05). Larval densities were similarly reduced in thiodicarb and thiodicarb-B. thuringiensis treatments. Treatments that contained cyhalothrin and/or profenofos provided the best control. Bacillus thuringiensis treatment of plots did not have any delayed effects on H. zea such as reductions in developmental rates or delayed mortality beyond 3 days after application. In addition, heliothine egg mortality in the 1994 collection 3 days after application did not differ significantly among treatments. Predator density in the B. thuringiensis alone treatment was similar to the untreated control. All treatments that contained conventional chemical insecticides, including thiodicarb at the ovicidal rate, reduced predator densities to low numbers. These data indicate that B. thuringiensis did not provide control of H. zea in cotton fields and did not improve control of H. zea when used in mixtures with an ovicide or larvacide. Therefore, caution should be urged in recommending B. thuringiensis when the heliothine species composition is skewed toward H. zea. Furthermore, when B. thuringiensis was used in mixtures with chemical insecticides, there was no conservation of arthropod predators relative to use of traditional chemical insecticide treatments.