Lepidopteran Communities in Two Forest Ecosystems During the First Gypsy Moth Outbreaks in Northern Michigan

We assessed lepidopteran communities in replicated stands representing two hardwood forest ecosystems in northern Michigan during a 3-yr period that coincided with the Þrst gypsy moth outbreaks experienced by this area.Adult Lepidoptera were collected at 4-wk intervals each summer in 1993Ð1995 in eight forest stands.Four stands were classiÞed as ecological landtype phase (ELTP) 20, and they were dominated by oaks (Quercus spp.), a favored host of gypsy moth, Lymantria dispar (L.).The other four stands were classiÞed as ELTP 45, and they were dominated by northern hardwood species with few preferred hosts of gypsy moth.Gypsy moth populations and defoliation ßuctuated dramatically in ELTP 20 stands during the 3 yr, reaching outbreak levels in at least one year in all four stands.In ELTP 45 stands, gypsy moth populations and defoliation were minimal.More than 12,000 adult Lepidoptera representing 453 taxa were collected from the eight stands.Lepidopteran species composition differed signiÞcantly between ELTPs for species collected in early season months (May and June), but not for late season months (July and August).Within ELTP 45 stands, abundance and species richness of Lepidoptera were not affected by differences between years, stands, or the interaction of the two factors.In ELTP 20 stands, the interaction of stand and year affected overall lepidopteran abundance and diversity of late season species.Species composition of late season lepidopteran communities in ELTP 20 stands may have been affected by gypsy moth population ßuctuations, although patterns were not consistent in all years.A subset of oak-feeding species appeared to be negatively affected during outbreak years, but other native Lepidoptera appeared to be resilient, perhaps reßecting the spatially and temporally limited duration of gypsy moth outbreaks.