Dispersal and development of bagworm larvae (Lepidoptera: Psychidae) on three host plants

The present study investigated the development and dispersal of bagworm larvae, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), on three hosts: arborvitae, Thuja occidentalis, blue spruce, Picea pungens, and juniper, Juniperus virginiana. The biomass of larvae was recorded at repeated intervals at 21 field sites. The relative quality of plants varied during larval development: early in the season, larvae were heavier on juniper and arborvitae than on blue spruce; late in the season, in contrast, larvae and pupae were lighter on juniper than on the two other plants. Larvae on blue spruce pupated later than those on arborvitae. In the laboratory, feeding rate and larval growth were not influenced by the density of larvae on the foliage of arborvitae up to a range which greatly exceeded that observed at any of our experimental sites. The incidence of dispersal among neonates emerging on arborvitae was high, as indicated by the high number of larvae captured on sticky traps, and the relatively low number of early instars on arborvitae foliage in relation to the reproductive output of females in the parental generation. The high rate of dispersal among early instars may be due to potential resource depletion over successive generations of bagworms.