Responses of sawfly larvae (Hymenoptera, Diprionidae) to the flavonoid taxifolin glucoside in their host plant were studied in a laboratory experiment. Larvae ofNeodiprion sertifer andDiprion pini were raised from egg hatch to cocoon spinning on two Scots pine (Pinus sylvestris) chemotypes, one without needle taxifolin glucoside (-) and the other containing 2-4% taxifolin glucoside (+). The (+) chemotype had somewhat lower concentrations of needle terpenoids (resin acids) than the (-) chemotype. Current-year needles had higher taxifolin glucoside concentrations than mature needles. There were no differences in survival or body size betweenN. sertifer larvae that fed on the (+) chemotype and those that fed on the (-) chemotype. FemaleD. pini larvae raised on (+) needles developed 6% more slowly than larvae fed (-) needles. The results from this study are contrary to earlier findings showing that flavonoid glucosides have strong negative effects on insect performance. Possible explanations for the different outcomes are discussed.