Great Basin Naturalist


The western spruce budworm (Choristoneura occidentalis Freeman) prefers to feed on flushing buds and current-year needles of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). Budworm larvae will not typically consume older age classes of needles unless all current-year foliage is depleted. We tested the following null hypotheses: (1) budworm larvae can feed on foliage with a wide range of qualities (i.e., current 1-, 2-, or 3-year-old needles) without measurable effects on fitness; and (2) budworm adults do not show any oviposition preference linked to the age of the foliage they fed on as larvae. We used both laboratory and field experiments. There was strong evidence to support rejection of hypothesis 1. Budworm larvae had greater survival from the 4th instar to pupal stage when they fed on current-year foliage (43%–52% survival) versus older age classes of foliage (0–25% survival). Pupae from current-year foliage were also heavier than pupae from ≥ 1-year-old foliage. There was weak evidence to support rejecting hypothesis 2; budworm adults that had fed on current-year or 3-year-old foliage as larvae preferred to oviposit on current-year foliage. Similar conclusions were drawn from the laboratory and field experiments.