EFFICACY OF AERIAL APPLICATIONS OF BACILLUS THURINGIENSIS BERLINER AND TEBUFENOZIDE AGAINST THE EASTERN HEMLOCK LOOPER (LEPIDOPTERA: GEOMETRIDAE)

Abstract

AbstractThe formulated product of the insect-molting hormone analog, tebufenozide (MIMIC 240LV), and two aqueous formulations of Bacillus thuringiensis subsp. kurstaki, ABG6387 and ABG6414, were aerially applied over prethinned commercial stands of balsam fir infested with the eastern hemlock looper. MIMIC® was applied once at the rate of 65.1 g active ingredient (ai) in 1.86 L/ha and twice at the rate of 33.4–35.4 g ai in 1.91–2.02 L/ha. The formulations of B. thuringiensis were applied twice at rates of 19.3–24.1 billion International Units (BIU) in 1.54–1.93 L/ha for ABG6387 and 33.2–36.0 BIU in 1.67–1.80 L/ha for ABG6414.Nine of the 10 plots treated with the single application of MIMIC showed reductions resulting from treatment, ranging from 3 to 93% within 9–11 days and 8 to 100% after 3 weeks. Plots treated twice with the lower dosage of MIMIC generally had larval population reductions of over 50% within 9–11 days of treatment and over 60% 3 weeks after treatment. For both treatments with MIMIC, plots with poor efficacy were clearly associated with low foliar deposition of the active ingredient. Overall, the results suggest that deposits of tebufenozide of less than 1.5 μg/g foliage do not give acceptable control of hemlock looper. Pupal population reductions resulting from treatment ranged from 8 to 99% for plots treated with the single application and 76 to 100% for plots treated twice at the half-dosage. Ground assessments of defoliation occurring after treatment ranged from 10 to 51% (year-old foliage) and 0 to 16% (current-year foliage) for the plots treated once, and 1 to 33% (year-old foliage) and 0 to 8% (current-year foliage) for the plots treated twice at the half-dosage. Thirty-five to 65% of year-old foliage and 15–39% of current-year foliage was defoliated in untreated check plots.Reductions resulting from treatment by ABG6387 ranged from 27 to 91% 10 days after the first application, from 73 to 99% 8 days after the second application, and from 90 to 100% for pupae. Plots treated with ABG6414 had larval population reductions from 76 to 93% 10 days after the first application and from 98 to 100% 7 days after the second application. No pupae were recovered in the plots treated with ABG6414. Defoliation assessed from ground level was less than 5% in the plots treated with ABG6387 and ABG6414 compared with defoliation of 10–29% of year-old foliage and 8–12% defoliation of current-year foliage in the check plots.