Abstract Forest tent caterpillar, Malacosoma disstria Hbn., behavioral and developmental interactions with 15 hybrid Populus spp. clones were studied in laboratory and glasshouse trials. Significant differences in larval preference and performance among the clones were found. Larval development time ranged from 30 to 52 days. Second-instar preference and larval development were significantly correlated, but 4th-instar preference and larval development were not. Second- and fourth-instar preferences were not correlated. Clonal productivity and tolerance of defoliation varied significantly, but were not correlated. The relationships between productivity, defoliation tolerance, and insect resistance were examined in regard to plant defense theory, host plant resistance, clonal selections for tree improvement, and assay utility. For. Sci. 40(4):686-714.