What lies beneath? Linking litter and canopy food webs to protect ornamental crops

The main research question of this thesis was how interactions between above-ground and below-ground food webs affect biological control. Arthropod food webs associated with plants are commonly composed of several species of herbivores, the detritivore community, specialist and generalist predators and parasitoids that feed on the first two groups and on each other. Populations of generalist predators can persist in crops by feeding on different species of pests, plant-provided food sources such as pollen, and on organisms of the detritivore community. The study system used here was rose plants infested by thrips and other pest species which are attacked by generalist predators. I first investigated the effect of a mixed diet of above-ground plant pests on life history traits of a generalist below-ground predator, Balaustium leanderi, which also forages on the above-ground plant parts. Secondly, I further investigated generalist predators that link above-ground and litter food webs. The canopy-dwelling predator, A. swirskii mainly inhabits the above-ground plant parts feeding on thrips but makes excursions to the litter layer where it feeds on alternative prey. Subsequently, I investigated the effect on thrips control of litter-inhabiting predators plus alternative prey (in the litter) present in commercial rose production greenhouses. Finally, I investigated the combination of species of canopy-dwelling and litter-inhabiting predator species and alternative food (on canopy and litter) for predators on thrips control. In this thesis I showed that linking above-ground and below-ground food webs through the addition of alternative food, can have a positive effect on biological control.