Insect invasion biology and agriculture are intimately related because many agricultural insect pests are recent invaders. In this presentation, we propose to summarize some of the main results that were recently obtained in ecology and evolutionary biology that are important to understand invasions. We also present population genetics studies on invasion routes whose conclusions lead to fundamental questions in ecology and in insect pest management. In particular, we focus on several aspects of the invasion process at the population level that might help understanding the success of invasion: multiple introductions, genetic bottlenecks, admixtures and the bridgehead scenario. To illustrate these points, we mainly focus on the western corn rootworm and the harlequin ladybeetle invasion history. The bridgehead invasion scenario, in which an invasive population is the source of other invasive populations, is evolutionarily and ecologically parsimonious, and may have played a crucial role in insect invasion biology. The question of the role of multiple introductions and admixture is discussed in an evolutionary context.