Competitive Interactions Between Generalist Predators and Their Effects on Shared and Non-Shared Pests in a Greenhouse Crop

Generalist predators are increasingly used in biological control because they can target multiple pests and persist in crops through supplemental feeding. However, when multiple generalist predators are released together, they may compete for shared food sources or engage in intraguild predation, potentially compromising suppression of shared and non-shared pests. Here, we investigated the interactions between two commercially used biological control agents, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) and Transeius montdorensis (Schicha) (Acari: Phytoseiidae) on greenhouse chrysanthemum. In a first experiment, we evaluated their population dynamics when offered a supplemental food source. Both predators negatively affected each other's abundance to a similar extent, but coexisted for several generations, despite O. laevigatus being a known intraguild predator of phytoseiid mites. In a second experiment, we assessed the pest control efficacy of single and combined predator releases against the shared prey Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and the non-shared prey Aphis gossypii Glover (Hemiptera: Aphididae). All predator treatments effectively suppressed thrips, though T. montdorensis alone exhibited slightly delayed suppression. Aphid numbers remained low even when O. laevigatus populations were reduced through intraguild predation. Meanwhile, T. montdorensis densities increased in the presence of aphids, likely due to feeding on aphid honeydew. Our results show that intraguild predation between these predators did not compromise the control of shared and non-shared pests under the tested conditions. Nevertheless, intraguild predation reduced the abundance of the predator responsible for aphid suppression; thus under stronger or earlier aphid pressure, control of the non-shared pest could be compromised. These complexities highlight the importance of considering both direct trophic interactions and alternative food use when designing multi-predator biological control strategies.