European and American populations of the parasitoid Cotesia glomerata show pronounced differences in foraging behavior across plants and leaves. This variation in spatial aspects of foraging behavior was observed about 350 generations after the introduction of C. glomerata from Europe to North America. We used a simulation model to study how these behavioral differences affect lifetime reproductive success in environments that differ in the spatial distribution of hosts. The preferred gregarious host Pieris brassicae occurs in rare large clusters in Europe but is absent in North America. The solitary caterpillars of Pieris rapae are negative binomially distributed across plants during summer in North America, whereas they are Poisson-distributed in Europe, and early and late in the season in North America. Simulations showed that the foraging strategy of American C. glomerata resulted in a higher lifetime reproductive success than did the strategy of European C. glomerata on a Poisson P. rapae distribution, but did not differ on the more clustered negative binomial distribution. American parasitoids spend less time on exploration flights, focusing on the exploitation of P rapae patches. This suggests that C. glomerata has adapted to the North American environment through the loss of exploration traits necessary for the location of rare clusters of P brassicae. Lifetime reproductive success of the European strategy was most sensitive to an increase in the giving up time on infested leaves. This behavioral parameter was more than twice as high in the American parasitoids compared with their European conspecifics. Reproduction; Evolution; Variation; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land and freshwater zones Pieris (Pieridae); Hymenopteran parasites; Cotesia glomerata; Parasite foraging behaviour & reproductive success relations; Nearctic region & Palaearctic region; Nearctic region; North America; Palaearctic region; Europe; Hymenopteran parasite foraging behaviour & reproductive success relations, geographical variation Cotesia glomerata (Braconidae); Reproductive productivity; Reproductive succes; Natural selection; Behavioural variation; Lepidopteran hosts; Pieris; Nearctic region & Palaearctic region; Nearctic region; North America; Palaearctic region; Europe; Parasite foraging behaviour & reproductive success relations, geographical variation none