PERFORMANCE OF WILD VERSUS LABORATORY POPULATIONS OF WESTERN SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE) FEEDING ON DOUGLAS-FIR FOLIAGE

Late-instar western spruce budworm, Choristoneura occidentalis (Freema n), larvae from wild and laboratory populations were reared on Douglas -fir, Psuedotsuga menziesii (Mirb.) Franco, foliage in the field to de termine if the two populations differed in terms of survival and repro duction (wild versus laboratory treatments). We also examined the effe ct of phenological age of Douglas-fir foliage (early season versus lat e season) on laboratory-reared budworm performance (laboratory versus late laboratory treatments). There was no evidence that survival from the late larval to pupal stage varied between the wild versus laborato ry treatments nor between the laboratory versus late laboratory treatm ents. Survival from the pupal to adult stage was significantly higher for the wild population compared with the laboratory population but wa s equivalent for the laboratory and late laboratory treatments. The pe rcentage of F1 egg masses with viable eggs was equivalent for the wild versus laboratory treatments, and for the laboratory versus late labo ratory treatments. Likewise, there were no detectable effects from pop ulations or foliar phenology on size of the F1 egg masses, number of e ggs per mass, or the number of F1 larvae hatching from each egg mass. Budworm population growth, estimated from the experimental data, did n ot vary dramatically between the wild versus laboratory treatments nor between the laboratory versus late laboratory treatments. Our results indicate it is valid to use laboratory-reared western spruce budworms to predict responses of wild populations. The absence of strong effec ts related to foliar phenology may imply that the budworm can survive and reproduce well on a broad range of foliage qualities.