Invasive arthropod generalist predators alter biological control

Exotic arthropod predators have invaded many communities worldwide, including agroecosystems. Indeed, some of the most well-studied invasive arthropod generalist predators (AGP) commonly occur in agricultural fields. Disturbance appears to favor invasion by exotic AGP, and as disrupted systems agroecosystems may be particularly inviting to new invaders. Often, invasive AGP displace similar native AGP species. Generalist predators fill complex ecological roles, preying on herbivores and thus strengthening biological control, but also feeding upon other biological control agents and thus weakening biological control. Invasive AGP often reach far higher densities than do the native generalist predator species they replace, intensifying these positive and/or negative effects on herbivore suppression. In some cases, “invasional meldown” occurs, wherein invasive AGP worsen the damage done by invasive herbivores by disrupting biological control. In other cases, however, “invasional reconstruction” occurs, wherein invasive AGP serve as key biological control agents of particularly damaging invasive herbivores. Examples of a mix of positive and negative effects on pest suppression have been reported for invasive ladybeetle, ground beetle, ant, wasp, and praying mantid species. In summary, it may be difficult to generalize effects of invasive AGP as consistently beneficial or harmful to pest management. Rather, the net impact of invasive AGP in a given agroecosystem likely will depend upon the particulars of species composition and structure, and the attributes of particular invasive AGP species.