Abstract During a genecological study of the red-black spruce complex in central New Brunswick, it appeared that severity of spruce budworm defoliation was related to the genotype of the individual trees. The closer an individual tree approximated red spruce, the greater the severity of budworm defoliation. This relationship was tested by rating foliage samples, obtained from red, black, and introgressed spruce, in respect to budworm defoliation. The correlation between budworm defoliation and genotype, as determined by a hybrid index system, was highly significant.