No regulatory role for adult predation in cyclic population dynamics of the autumnal moth,Epirrita autumnata

Abstract

1. Multiannual population cycles of geometrid moths are thought to be driven by trophic-level interactions involving a delayed density-dependent component. Predation on adult moths has been a little-studied mechanism of this phenomenon. 2. Using 29 daytime and 61 night-time predation trials in the field, we exposed living autumnal moth (Epirrita autumnata Borkhausen, Lepidoptera: Geometridae) females to their natural predators during each autumn throughout the 10-year population cycle. 3. In our northern study location (70°N), insectivorous passerines had already migrated, and harvestman Mitopus morio Fabricius (Opiliones: Phalangiidae) was found to be the main predator of the adult moths. The predation mortality occurred mainly at night and was positively correlated with the minimum temperature measured during the predation trial. 4. Despite high annual variability in the degree of adult predation, both direct and delayed density-dependent effects were weak and indicate that predation on adult moths in the autumn does not have any regulatory role in cyclic population dynamics of the autumnal moth in northern Fennoscandia.