Good and bad traits of Harmonia axyridis - from biological control to invasion.

The ladybird, Harmonia axyridis, was introduced from Asia as a biological control agent of aphid and coccid pests and has been very successful in this respect. The coccinellid established but became invasive in surrounding regions and has been reported to have undesirable negative impacts on native aphidophagous guild members, cause nuisance problems in residential areas and also plant damage. This makes H. axyridis an excellent case study to identify the traits that make a predator an attractive and effective biological control agent and those that lead us to categorise it as an alien invasive species. A number of these traits can be both “good” and “bad” when viewed in either a biological control context or in an ecological context. In this paper we discuss the relative merits of traits that are commonly associated with biological control agents (voracity, prey searching efficiency, tolerance to pesticides) along with those less often considered, but that we believe are of equal importance, including overwintering potential, phenotypic adaptability and intraguild interactions with native aphidophagous species. The consequences of these traits on species diversity and the control of pest species in the introduced range will be discussed.