Weak responses of pine sawfly larvae to high needle flavonoid concentrations in scots pine

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.