Untangling parasitoid competition: A three-dimensional framework for parasitoid interactions in biological control

Parasitoid wasps are major biological-control agents, but their contribution to pest suppression is shaped by more than host attack. In agroecosystems, released and resident parasitoids interact with conspecifics, heterospecific parasitoids, predators, hyperparasitoids, alternative hosts, non-target species, and habitat resources. This review synthesizes parasitoid competition from a biological-control perspective and proposes a three-dimensional framework that classifies competitive interactions by competitor level, ecological arena, and interaction mode. The framework integrates intraspecific and interspecific competition, extrinsic and intrinsic interactions, community-mediated effects, and exploitative, interference, apparent, and mixed pathways. We emphasize that superparasitism and multiparasitism are not only behavioral or developmental phenomena, but also operational links between adult oviposition decisions, within-host outcomes, and field-level control. Competition can reduce effective parasitism, offspring fitness, parasitoid establishment, and native-guild persistence when niche overlap is high, yet its costs may be offset when species partition host stages, microhabitats or seasonal windows. We argue that biological-control success should be evaluated through a hierarchy of outcomes, including host mortality, parasitoid emergence, offspring quality, sex ratio, population persistence, pest-density trajectories, crop protection, and non-target risk. Finally, we translate this synthesis into management principles for species selection, release timing, release density, release ratio, and compatibility with other integrated pest management (IPM) tools. Understanding parasitoid competition is therefore essential for designing biological-control programs that are predictable, resilient, and ecologically safe.