Harmonia axyridis invasions: Deducing evolutionary causes and consequences

Abstract

AbstractI consider evolutionary approaches to deducing factors that have made the ladybird beetle Harmonia axyridis such a successful invader, and the contribution that studies of this species in its native range can make. Work aiming to demonstrate which (pre)adaptations have made the species so successful often fails to compare these putative characters with those of other ladybirds. This has led to a tendency for “argument by design”‐type claims on characters widely shared by non‐invasive coccinellids. There is good evidence from genetic studies that evolutionary change occurred in invasive populations, contributing to their success. There is some evidence for subsequent evolutionary change after the establishment of invasive H. axyridis, primarily in the native organisms with which the ladybird interacts. I show here that there appears to have been little adaptation in H. axyridis, over about 20 generations, to the alkaloids of one North American native intraguild prey, the ladybird Coleomegilla maculata. Studies of H. axyridis in its native range are important, as they provide a snapshot of the ancestral ladybird, unobscured by subsequent evolutionary change related to its invasiveness. They provide baseline data about phenomena such as interactions with natural enemies and intraguild predation, and they also can provide pointers as to how H. axyridis might further adapt in the regions it has colonized. Harmonia axyridis represents an ideal opportunity for greater international co‐operation between scientists studying this species in its native range in Asia and scientists studying it in Europe, America and Africa, where it is an invasive exotic.