Eleven peach cultivars were evaluated at Thorsby, Ala., and Byron, Ga., for bark prunasin content, bark thickness, peachtree borer larvae entrance sites, and peachtree borer adult emergence. Significant differences in larval weight occurred after 21 d of feeding on four different peach cultivars but were not evident after 42, 64, or 88 d. Prunasin content and bark thickness exhibited considerable variation with time, location, and cultivar. A significant positive correlation was found between prunasin content and emergence in 1 of 3 yr. In that year, larval entrance sites were positively correlated with emergence. This phenomenon was attributed to the presence of an ovipositional stimulant on trees that had previously supported the successful development of peachtree borers rather than an oviposition preference for trees with high prunasin content. A statistical correlation between peachtree borer emergence and bark thickness was not shown. However, the cultivar from which the greatest emergence occurred also had the greatest bark thickness. Results indicated that differences in host suitability exist among cultivars, but that host suitability may vary with environmental conditions.