none Most emerging 2nd-instar larvae of spruce budworm, Choristoneura fumiferana (Clem.), tested in the laboratory were photopositive and there was no difference in response between healthy larvae and larvae parasitized by Apanteles fumiferance Vier. The vertical distribution of dispersing, parasitized larvae caught on sticky traps more closely resembled that of established larvae than it did the vertical distribution of the overwintering populations. This indicates that there was some differential redistribution of parasitized and nonparasitized individuals. Despite these differences, the estimate of parasitism by A. fumiferanae based on mid-crown branch samples in justified because it is most consistent and most closely reflects the overall frequency of parasitism.