FEEDING PREFERENCES OF 4TH-INSTAR AND 6TH-INSTAR SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE) LARVAE FOR FOLIAGE EXTRACTS FROM YOUNG AND OLD BALSAM FIR HOSTS

Feeding behavior of fourth- and sixth-instar spruce budworm, Choriston eura fumiferana Clem., toward aqueous extracts of balsam fir (Abies ba lsamea (L.) Mill.) foliage from terminal and lateral shoots of young a nd old trees is described. Fourth instars prefer extracts from termina l shoots of young and old trees. This feeding preference is correlated with the content of N in the foliage and the feeding rate is correlat ed with the N/tannin ratio. Sixth instars show a strong preference for extracts from lateral shoots of young trees. Their feeding preference is correlated with the sucrose content of the foliage, whereas their feeding rate is correlated with the glucose content. Age-related varia tion in budworm larval feeding preference may be an important evolutio nary adaptation for the spruce budworm, enabling it to respond positiv ely to naturally occurring seasonal changes in the nutritional quality of its host plant and to chemical changes induced by defoliation.