| Insect pests are the biggest threat for agricultural and forestry. New pest control methods are needed since problems with plant pests are expected to increase. Unlike other pest control methods, omnivorous predators can provide a unique dual function in plant protection: as predators and plant defence inducers. Omnivores can reduce pest density by direct predation and indirect induction of plant defences that decrease pests’ performance and attract natural enemies. We found that plants fed by omnivores were more attractive for natural enemies and less attractive for herbivores than clean plants, and herbivores had lower performance on these plants than on clean plants. Thus, omnivores could enhance plant resistance against pests and recruit more bodyguards for plants, resulting lower pest density. Thus, omnivores can strongly impact on natural enemy on the same plants via plant and herbivore-mediated effects, which has been ignored until now.
In this project, we aim to 1) assess the plant and herbivore-mediated effects of omnivorous predators on performance of natural enemy under lab conditions, 2) uncover these effects on natural enemy communities in open fields, 3) disentangle the mechanisms of the omnivore-altered multi-trophic interactions, and 4) evaluate the consequences of these interactions on the population dynamics of herbivores, natural enemies and omnivores.
We will use one important Swedish crop (oilseed rape, Brassica spp.) and its associated insects as model system. To do so, we will study the preference of natural enemies for clean and omnivore-induced plants with herbivores grown omnivore-induced and clean plants in the lab. We will evaluate the performance (survival rate, development, biomass, and sex ratio) of natural enemies developed on herbivores developed on omnivore-induced and clean plants. To understand these effects on natural enemy communities, we will compare the predation and parasitism rates and the attractiveness of parasitoids on omnivore-induced and clean plants in the field. To understand the underlying mechanisms, we will quantify plant volatiles and metabolites induced by the omnivore. Furthermore, we will study population dynamics of herbivores, parasitoids and omnivores using cages experiments in the greenhouse, to understand how omnivores alters the multi-trophic interactions and the consequences on herbivore density.
This project will be the first to quantify the plant and herbivore-mediated effects of omnivores on natural enemies from individual to community level in an open field crop system. Experts from different universities within (SLU and Umeå University) and outside (Wageningen University & Research) Sweden and private sectors will collaborate on this project. Results obtained will provide knowledge base for game-changing plant protection strategies, meeting the goals of sustainable, environmental friendly and effective plant protection.
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