In this study, the effects of secondary metabolites on the feeding preference and growth of generalist caterpillars, Agelastica alni L., were investigated. Feeding experiment has been applied with a total of 11 diet; 6 of which were prepared by adding different concentrations of gallic acid (1, 3, 5 %) and quinine (0.125, 0.25, 0.5 %) to the control diet, 3 diet of which prepared by adding different concentrations of gallic acid and quinine. According to the results, the amount of gallic acid consumed did not affect the food consumption and the amount of pupa lipids. However, the amount of gallic acid consumed positively affects the pupal mass and the pupal crude protein. In addition, the amount of quinine consumed negatively affected the developmental performance of larvae except for the food consumption. As the count of secondary metabolites in the diet increases, the pupal mass and the pupal crude protein decrease. Overall, during the co-evolution processs, A. alni larvae may be able to adapt to gallotannins. However, quinine, an alkaloid, is a feeding deterrence and growth suppressor for larvae.