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Title: EFFECTS OF DIFLUBENZURON AND SINGLE AND DOUBLE APPLICATIONS OF BACILLUS THURINGIENSIS ON GYPSY MOTH LARVAL DENSITY, DAMAGE, AND POPULATION REDUCTION

Author
item THORPE, KEVIN
item Ridgway, Richard
item WEBB, RALPH

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The microbial agent, Bacillus thuringiensis (B.t.), and the chemical insecticide, diflubenzuron (Dimilin), are commonly used in aerial spray programs against the gypsy moth, the most important defoliator of hardwood trees in the northeastern United States. Direct experimental comparisons of the effectiveness of these materials are needed to make informed gypsy moth management decisions. In this study, Dimilin, or single or double applications of B.t. were aerially to forested plots at each of four locations in Talbot County, MD. The effectiveness of the treatments was determined from measurements of caterpillar density, defoliation, and reduction in egg mass numbers. The greatest reduction in caterpillar numbers (73-83%) occurred in plots treated with Dimilin or two applications of B.t. A single application of B.t. reduced caterpillar numbers by 55%. However, while all treatments provided acceptable foliage protection, there were no detectable differences among the treatments. None of the treatments reduced subsequent egg mass numbers. These results should help gypsy moth managers choose the most appropriate treatments for their specific management goals.

Technical Abstract: The effectiveness of aerial applications of insecticides was tested in a randomized block design at four locations in Talbot County, MD. The study compared single and double applications of Bacillus thuringiensis Berliner subsp. kurstaki (74.1 billion international units/ha per application), difulbenzuron (69 g [AI]/ha), and no treatment. Treatment effects were estimated from frass collections, defoliation, counts of pupae under burlap, and egg-mass counts. Estimates of larval density in the canopy on May 31 (20 d after the diflubenzuron and first B. thuringiensis application, and when larvae were predominately in the third and fourth instars) ranged from 318.3 to 55.5 larvae per m2 in the controls and diflubenzuron-treated plots, respectively. Larval density was reduced with all treatments, and was lowest in the plots treated with diflubenzuron and two applications of B. thuringiensis. Population density rapidly declined in the control plots, and by June 20, when larvae were predominantly in the fifth and sixth instars, no significant differences in larval density were detected among the treatments. Significantly less defoliation occurred to oak trees in the treated plots, but no differences were detected among the spray treatments. Counts of pupae under burlap, post-season egg-mass counts, and percent reduction in egg-mass density did not differ significantly among treatments or versus controls.