Friends or frienemies? The community ecology of greenhouse biocontrol

Introducing multiple predators to manage greenhouse pests generates complex food webs that may have beneficial or detrimental impacts on predators and their respective preys. We conducted a microcosm experiment to observe the effect of commonly introduced predators, Neoseiulus cucumeris Oudemans, Stratiolaelaps miles (Berlese), and Atheta coriaria (Kraatz), and combinations of these predators on organisms in greenhouse communities. Each microcosm was comprised of an individually caged marigold (Tagetes patula) infested with greenhouse pests (e.g. thrips and fungus gnats) and seeded with one the following predator treatments: 1) No predators-control, 2) N. cucumeris, 3) S. miles, 4) A. coriaria, 5) N. cucumeris + S. miles, 6) N. cucumeris + A. coriaria, 7) S. miles + A. coriaria, and 8) All predator species. Microcosms were arranged on greenhouse benches in a randomized complete block design with 5 blocks and 8 replicates per treatment per block. Each week, five microcosms per treatment were destructively sampled for organisms. The numbers of pests, predators, and other organisms in the plant canopy and soil were measured and compared. We found that interactions among introduced predators and pests impacted community composition in the microcosms over time. The effect of shared food resources on the microcosm communities and implications for biocontrol of greenhouse pests are discussed.