Specialization is a central concept in ecology and one of the fundamental properties of parasitoids. Highly specialized parasitoids tend to be more efficient in host-use compared to generalized parasitoids, presumably owing to the trade-off between host range and host-use efficiency. However, it remains unknown how parasitoid host specificity and host-use depends on host traits related to susceptibility to parasitoid attack. To address this question, we used data from a 13-year survey of interactions among 142 aphid and 75 parasitoid species in nine European countries. We found that only aphid traits related to local resource characteristics seem to influence the trade-off between host-range and efficiency: more specialized parasitoids had an apparent advantage (higher abundance on shared hosts) on aphids with sparse colonies, ant-attendance and without concealment, and this was more evident when host relatedness was included in calculation of parasitoid specificity. More traits influenced average assemblage specialization, which was highest in aphids that are monophagous, monoecious, large, highly mobile (easily drop from a plant), without myrmecophily, habitat specialists, inhabit non-agricultural habitats and have sparse colonies. Differences in aphid wax production did not influence parasitoid host specificity and host-use. Our study is the first step in identifying host traits important for aphid parasitoid host specificity and host-use and improves our understanding of bottom-up effects of aphid traits on aphid-parasitoid food web structure.

CSIRO GPO Box 2583 Brisbane QLD 4001 Australia Institute of Zoology Faculty of Biology University of Belgrade Belgrade Serbia

Department of Integrative Biology University of Guelph Guelph Ontario Canada Agrarökologie Georg August Universität Göttingen Germany

Faculty of Agriculture University of Belgrade Belgrade Zemun Serbia

Institute of Zoology Faculty of Biology University of Belgrade Belgrade Serbia

Laboratory of Agricultural Zoology and Entomology Department of Crop Science Agricultural University of Athens Athens Attica Greece Laboratory of Agricultural Entomology Department of Entomology and Agricultural Zoology Benaki Phytopathological Institute Attica Greece

Laboratory of Aphidology Department of Experimental Ecology Institute of Entomology Biology Centre Academy of Sciences of the Czech Republic ČeskéBudějovice Czech Republic

Laboratory of Entomology and Agricultural Zoology Department of Agriculture Crop Production and Rural Environment University of Thessaly Magnissia Greece

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