Efficacy of RH5992, a new insect growth regulator against spruce budworm (Lepidoptera: Tortricidae) in a boreal forest

A field trial was conducted in 1993 to determine the efficacy of tebufenozide (RH5992) against spruce budworm, Choristoneura fumiferana (Clemens). An aqueous commercial formulation (Mimic 2F) was sprayed aerially with a Cessna 188 Ag-truck equipped with 4 rotary atomizers. Five application strategies involving single and double applications, 2 dosages (70 and 140 g [AI]/ha), and 3 application volumes (1, 2, and 4 liters/ha) were compared with an untreated control. The phenological development and larval and pupal weights of spruce budworms treated with tebufenozide differed significantly from those in the control. A double application at 70 g (AI) in 2 liters/ha was the most effective treatment in suppressing budworm populations and protecting balsam fir from defoliation. Single applications of 70 g (AI) in 1 and 2 liters/ha and 140 g (AI) in 4 liters/ha suppressed budworm populations to mean levels that were significantly lower than the control populations. However, 70 g (AI) in 2 liters/ha was the only treatment that prevented significant (>20%) defoliation of balsam fir. Larval survivorship and percentage of population reductions observed after a single application of 70 g (AI) in 4 liters/ha were not significantly different from those in the control. These findings suggest that the number of spray applications and the concentration (g [AI]/liter) of the tank-mix are as important as the dose per se, in determining a successful application strategy.