Bottom-up (host plant) and top-down (natural enemy) pressures both can affect how insect herbivores select their host plants. Here we investigated which fall webworm (Hyphantria cunea, hereafter FW) parasitoids, an important natural enemy for FW, attack FW at different ontogenetic stages in the field on different host plants. To determine whether FW parasitism was dependent on the FW developmental stage, we placed FW early (8-10 days till hatching) and late term (12-13 days till hatching) eggs and 10-day old larvae, and 20-day old larvae at field sites in Boulder, Colorado (USA). We deployed both the eggs and larvae on 4 host plants commonly eaten by FW in Colorado: chokecherry, black willow, narrowleaf cottonwood, and thin-leaf alder. We kept eggs and larvae at the field sites for one week before retrieving these samples. We are currently rearing collected FW eggs and larvae to pupation in the lab and collecting emerging parasitoids. All parasitoids will be identified to the lowest taxon possible. Our results will contribute to understanding the ontogenetic stages that specific parasitoid species attack. Our research will help us to understand the host selection process among parasitoids of a local herbivore.