EFFECTS OF FOREST FRAGMENTATION ON THE POPULATION-STRUCTURE OF THE WINTER MOTH OPEROPHTERA-BRUMATA L (LEPIDOPTERA, GEOMETRIDAE)

The spatial distribution and genetic population structure of the winte r moth (Operophtera brumata) are related to the isolation and area of woodland fragments in N. Belgium. Densities which are very small, are negatively associated with isolation and positively with area, and win ter moth is absent from some habitat patches. Twenty-five percent of t he within-subpopulation genetic variation (H(exp)) seems to be lost by the isolation of the woodlots, the genetic heterogeneity among subpop ulations is intermediate (G(st) = 0.02) and the REML dendrogram follow s the geographical pattern of the study plots, indicating that there i s an effect of geographical distance between subpopulations on top of the isolation effect. In genetically less variable subpopulations, mal e moths weight less which might result from a worse synchronization of larval hatching with host tree bud burst.