Protecting the good guys from the good guys: Optimizing multiple predator biological control systems

Introducing generalist predators for greenhouse pest management generates complex food webs that may have beneficial or detrimental impacts on predators and their respective preys. Our previous work demonstrated that introducing Neoseiulus cucumeris predatory mites using ‘breeder piles’ was detrimental for N. cucumeris when the soil-dwelling predators, Stratiolaelaps miles and Atheta coriaria, were present. Negative impacts on N. cucumeris were likely due to intraguild predation among predators. Furthermore, negative interactions reduced thrips suppression. To optimize the combined use of these predators we observed ‘hanging sachets’ that placed N. cucumeris in the plant canopy away from soil predators as an alternative application method. Our experiment was conducted in a commercial greenhouse and consisted of a randomized complete block design with four treatments: breeder piles, hanging sachets, bran piles (without mites), and sawdust piles. There were 5 blocks and 10 replicates per treatment per block. Each week, five samples per treatment were randomly selected and sampled for organisms. The numbers of N. cucumeris were measured and compared among treatments. Atheta coriaria numbers were also measured and compared. We found six- to eight- fold more N. cucumeris mites in hanging sachets compared to breeder piles in both trials (ANOVA, P<0.05). There were significantly more A. coriaria in breeder and bran piles compared to other treatments (Kruskal-Wallis, P<0.05) and overall few A. coriaria in hanging sachets and sawdust piles. Our results show that hanging sachets partition the habitats of N. cucumeris and A. coriaria, thus reducing their encounters and promoting their compatibility for greenhouse biocontrol.