Patterns of 2-year population cycles in spatially extended host-parasitoid systems.

Coexisting but temporally separated cohorts of insects with a multiannual life cycle may have dissimilar average abundance, resulting in periodically fluctuating population density. In the case of the boreal moth genus Xestia with a 2-year life cycle and a distinct abundance difference between the two coexisting cohorts, empirical results and a simple model suggest that the oscillatory dynamics are maintained by interaction with a parasitoid wasp. Here we report theoretical results on a spatially extended version of the basic model and relate the modeling results to empirical observations. A spatially extended model may have domains oscillating in different phases as is the case between western and eastern Finnish Lapland. Spatial heterogeneity tends to fix the location of phase boundaries. In contrast, spatially homogeneous temporal fluctuations tend to synchronize populations in large regions.