Elements of Population Dynamics of Bagworm (Lepidoptera: Psychidae) on Hedge Rows of White Pine

Abstract

Spatiotemporal elements related to the population dynamics of bagworms, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), on white pine, Pinus strobus (L.), were investigated by sampling populations of bagworms repeatedly at 12 sites within a 50-km radius in central Indiana. The number of live bagworms declined over time by up to 95% in some sites, and the rate of population decline increased with the initial density of larvae. A comparison of population density of bagworms in past generations with that of the current-year generation revealed that sites heavily infested with bagworms from previous years carried a high number of live larvae early but not late in the season. The positive relationship between densities of bagworms in past and current generations observed at five of 12 sites suggests that larvae commonly do not disperse when they emerge on a suitable host. However, there was considerable variation relative to this pattern, suggesting that dispersal is common as well. Pupation and emergence of adults occurred in late summer and early fall, with some level of phenological asynchrony observed at different sites. Dates corresponding to 50% pupation or adult emergence varied by up to 12 d at different sites. Males suffered higher mortality than females during the pupal stage. The positive correlation between the mortality level of female pupae and previous years' population density may be related to a buildup of populations of natural enemies in sites that were previously heavily infested with bagworms.