EFFECTS OF DOUGLAS-FIR FOLIAGE AGE CLASS ON WESTERN SPRUCE BUDWORM OVIPOSITION CHOICE AND LARVAL PERFORMANCE

The western spruce budworm (Choristoneura occidentalis Freeman) prefer s to feed on flushing buds and current-year needles of Douglas-fir (Ps eudatsuga menziesii [Mirb.] France), Budworm larvae will not typically con consume older age classes of needles unless all current-year foli age is depleted. We tested the following null hypotheses: (1) budworm larvae can feed on foliage with a wide range of dualities (i.e., curre nt-year versus 1-, 2-, or 3-year-old needles) without measurable effec ts on fitness; and (2) budworm adults do not show any oviposition pref erence linked to the age of the foliage they fed on as larvae. We used both laboratory and field experiments. There was strong evidence to s upport rejection of hypothesis 1. Budworm larvae had greater survival from the 4th instar to pupal stage when they fed on current-year folia ge (43%-52% survival) versus older age classes of foliage (0-25% survi val). Pupae hem current-year foliage were also heavier than pupae from greater than or equal to 1-year-old foliage. There was weak evidence to support rejecting hypothesis 2; budworm adults that had fed on curr ent-year or 3-year-old foliage as larvae preferred to oviposit on curr ent-year foliage. Similar conclusions were drawn from the laboratory a nd field experiments.