Thuricide® (a microbial insecticide having 30 × 109 spores of Bacillus thuringiesis Berliner per gram) applied on apple for control of the eye-spotted bud moth, Spilonota ocellana (Denis and Schiffermüller), apparently retarded spring larval development and produced noticeably smaller larvae. Mortality of the spring larvae in the Thuricide-treated section was 16.5% on Red Delicious and 18.7% on Cortland. In the check only 1.5% and 9.5% mortality occurred on Red Delicious and Cortland respectively. Significantly greater numbers of summer larvae were collected in the check than in the treated sections Reared adult moths from the Thuricide block were significantly smaller than those from the check. This size difference was greater with later adult formation periods. The length and width of both males and females in the Thuricide-treated section decreased significantly with later formation periods but increased significantly in size in the check with later formation periods. The immediate effects of Thuricide on the eye-spotted bud moth population were not considered economic control; however, the long-range effects might be promising.