Aerially applied Thuricide 48LV, Thuricide 64B, Futura XLV, and water-based formulations of Bacillus thuringiensis Berliner var. kurstaki (B.t.), were tested for effectiveness to control the hemlock looper, Lambdina fiscellaria fiscellaria (Guen.), in balsam fir, Abies balsamea (L.) Mill., stands. Thuricide 64B, applied twice at a dosage of 30 Billion International Units (BIU) per hectare in 1.78 L/ha, was the most effective, reducing the larval population by 100%.