Novel genotypes often arise during biological invasions, but their role in invasion success has rarely been elucidated. Here we examined the population genetics and behavior of the fungus, Leptographium procerum, vectored by a highly invasive bark beetle, Dendroctonus valens, to determine whether genetic changes in the fungus contributed to the invasive success of the beetle–fungal complex in China. The fungus was introduced by the beetle from the United States to China, where we identified several novel genotypes using microsatellite markers. These novel genotypes were more pathogenic to Chinese host seedlings than were other genotypes and they also induced the release of higher amounts of 3-carene, the primary host attractant for the beetle vector, from inoculated seedlings. This evidence suggests a possible mechanism, based on the evolution of a novel genotype during the two or three decades since its introduction, for the success of the beetle–fungal complex in its introduced region.