Non-consumptive intraguild interactions and their relevance to biological control

Abstract: The effects of intraguild predation (IGP) on biological control are strongly species- and context-dependent, ranging from negative to neutral to positive, requiring case by case scrutiny. To allow proper predictions of the relevance of IGP in a given setting, detailed knowledge of the direct and indirect intra- and extra-guild interactions, incl. how they ultimately affect the basal resource, the plant, is needed. Accordingly, there exist numerous studies on IGP between biological control agents. However, a common shortcoming in the understanding of the relevance of IGP in biological control is the almost exclusive focus on the consumptive (density-mediated) effects of IGP, largely disregarding non-consumptive (trait-mediated) intraguild effects. Non-consumptive predator effects modulate the behavior, physiology and morphology of prey, and translate into significant trait-mediated shifts in population and community structure and dynamics. Using predatory mite guilds as cases in point, I argue that, analogous to classical predation, trait-mediated effects of IG predators on IG prey may influence the outcome of biological control at least as strongly as do density-mediated IG effects.