Multiple resource supplements synergistically enhance predatory mite populations.

Many plants offer food rewards such as extrafloral nectar and food bodies, which have been shown to attract and retain entomophagous arthropods. In addition to food rewards, plants may possess structures that serve as shelter and/or oviposition sites for beneficial arthropods, so-called domatia. Acarodomatia are commonly used by beneficial mites for oviposition and protection from intraguild predators and adverse climatic conditions (drought). While in nature these food and shelter traits often occur in combination, they have been largely studied in isolation and we know little about how these traits interact, i.e., whether they act independently, antagonistically or synergistically. In the present study, we used citrus seedlings to test the impact of provisioning fibers (as a proxy for acarodomatia), as well as two different categories of food rewards (pollen and sugars) on oviposition and population development of phytoseiid mites. The highest oviposition and abundance of predatory mites was obtained in the treatment where the three resources were offered in combination. The combined impact of the three resources when provided jointly was up to five times higher than the summed impacts of each resource provided individually, thus providing evidence for a three-way synergy between the fibers, pollen and sugars. From an ecological point of view, our results demonstrate that combining multiple indirect defensive traits can strongly enhance the impact on the mutualistic arthropods. Differences in resource provisioning strategies in plant-phytoseiid and plant-ant mutualisms are being discussed. The presented results are of particular importance for our understanding of the functioning of defensive plant-arthropod mutualisms, as well as for the use of predatory mites in conservation- or inundative biological control.