Pollen Metabarcoding and Pollinator Networks
The pollen loads of 267 insects were successfully analyzed for plant family or genus composition. The total read count after filtering was 15,205,661 ranging from 22 (Sylvanelater cylindriformis ) to 2.7 M (Toxomerus marginatus ) (Supplementary Table 3). After removal of OTUs (operational taxonomic units) from negative controls, we found 129 plant genera with at least 98% hit match to reference library (Supplementary Table 4). As a more conservative estimate, 49 plant families were found across all insects (Supplementary Table 3, Figure 2). The relative abundance of sequence reads was used as a proxy of relative abundance of pollen load composition for the remaining analysis (Richardson et al. 2015, Kraaijeveld et al. 2015, Pornon et al. 2017).
All species, apart from one undetermined cecidomyiid had strawberry pollen on their bodies. Species with only strawberry pollen on their bodies were the dipterans Lucilia sericata, Liohippelates bishoppi, Discomyza incurva , the coleopterans Collops quadrimaculatus, Macrodactylus subspinosus, Sylvanelater cylindriformis , and the hemipteran Lygaeus kalmii (Supplementary Table 3). The most generalist families were Syrphidae (for which pollen data from 32 plant families, and 73 genera were recorded), Pollenidae (29 plant families, 55 genera), and Anthomyiidae (22 plant families, 43 genera). At first glance syrphids appeared quite generalist in their choice of flower visitations. However, this picture was driven by two generalist species (Toxomerus marginatus and Sphaerophoria scripta ) and the remaining species were more selective, carrying pollen from only 2-6 plant species (Figure 3).