Woody vegetation spread over former croplands in Europe has created new unexploited habitats for forest organisms. Their ability to colonise them and thrive depends on life-history traits including fecundity, dormancy and dispersal ability. The effects of these traits on species distribution, abundance and community assembly have been extensively studied in fragmented landscapes. However, their consequences for genetic diversity and connectivity in local populations remain largely unknown. We investigated the genetic population structure and diversity of Curculio elephas and Curculio glandium (Coleoptera: Curculionidae), two sympatric acorn weevils with contrasting life-history strategies, in a landscape with mature oak stands and plots of new expanding forests. Using a fragment of a mitochondrial gene cytochrome oxidase subunit 1 and nuclear DNA (80 single nucleotide polymorphisms [SNPs]), we found that gene flow between populations was significantly weaker in the poor disperser C. elephas, especially in isolated new forests. However, genetic neutrality tests did show population expansion in C. elephas, which suffers frequent population bottlenecks (probably linked to extended dormancy) and is a poor coloniser of isolated new forests. However, its greater fecundity allows it to recovery quickly if the number of reproductive individuals falls. Its populations are thus larger but genetically less diverse than those of C. glandium Within foraging guilds, the most fecund species will outcompete the others under a context of constrained dispersal. Hence, new landscapes of expanding forests represent a good opportunity for more mobile but less fecund species to colonise new habitats and so be temporarily released from competition.