Alien versus predator: unravelling the interactions between natural enemies

Abstract

Natural enemy complexes may contribute to the suppression of insect pest populations more effectively than single species. Understanding the interactions between natural enemies is essential if multiple species are to be exploited for pest management. Natural enemies can interact synergistically/ additively (e.g. the enhanced transmission and dispersal of insect pathogens by predators and parasitoids) or antagonistically (e.g. intra-guild predation (IGP) and competition). IGP occurs when competing species engage in predator-prey interactions. It is a process that is considered to be common and widespread in many ecological communities. The harlequin ladybird, Harmonia axyridis (Pallas) is an infamous intra-guild predator. It is a large, well-defended coccinellid with a wide-dietary range. Harmonia axyridis, originally from Asia, has been introduced into many countries as a biological control agent of aphids. In Europe small populations of H. axyridis were noted as established in the wild soon after release. It is now considered an invasive alien species because it poses a threat to native biodiversity. Field and laboratory studies have demonstrated the tendency for H. axyridis to act as a unidirectional intra-guild predator of many coccinellid species. Recent evidence from Europe, using large-scale and long-term distribution and abundance data, has highlighted declines in widespread and common coccinellids following the arrival of H. axyridis. Evidence is emerging that the deleterious effects of H. axyridis on native communities are far-reaching. Unravelling the complex interactions between species within a community context is essential for effective pest management and critical to assessing the risks (and benefits) of exotic biocontrol agents